Applications of Redispersible Powders

Polymer Dispersions and Their Industrial Applications. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. KGaA ISBNs: 3-527-30286-7 (Hardback); 3-527-60058-2 (Electronic)

329

13

Applications of Redispersible Powders
Hermann Lutz and Christoph Hahner

13.1

Introduction

The building/construction industry is the main industry for redispersible powders. Over the years the usage of dry mortar technology has been developed dramatically and modernized the way mortars are being used on a job-site. The invention of redispersible powders enabled the industry for the first time to produce pre-packed, polymer modified building materials that needed only the addition of water before application. These materials, known as dry mortar mixes guarantee defined and consistent performance of construction materials. In the past up until to the 1950s mortars were exclusively used and applied as jobsite mixed mortars, where the mineral binder (mostly cement) and the aggregates (mostly silica sand) were transported separately to the job-site. The aggregates and the mineral binders were then mixed together by hand in the appropriate ratio and were gauged with water in order to obtain the fresh mortar ready to apply. During the 1950s and 1960s both in Western Europe and the US, but especially in Germany, there was a fast growing demand in the construction industry for new building materials and technologies. Several reasons, like shortage of skilled workmen, the need of shorter construction time together with cost reduction, increasing labor costs, the diversification of building materials suitable for specific applications, the request for new materials and an increased demand for better quality of constructions were supporting a movement towards dry mix mortar technology. The job-site mix mortar technology is not able to meet adequately all these requirements. As a practical consequence, the development of the modern construction and building chemical industry in the countries of the West from the 1960s onwards was influenced mainly by two important trends, which can be seen nowadays in the whole world. First there was a replacement of the job-site mixed mortars by premixed and pre-packed dry mix mortars, which are more and more applied with machines. Secondly mortars started to be modified with polymer binders in order to improve the product quality and to meet the requirements of the modern building industry. As a consequence the two-pack systems (mortar + dispersion) as well as

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13 Applications of Redispersible Powders

ready to use products (liquid or paste) were substituted by one-pack systems, which are modified with redispersible powders, pre-mixed and pre-packed dry mix mortars.

13.2

Manufacturing of Redispersible Powders

A redispersible powder is by definition a polymer in a powdered form that can be redispersed by adding water to it. The resulting emulsion will fulfill the functionality of a polymeric dispersion binder, normally within a cementitious or gypsum based system. Redispersible powders are manufactured by spray drying an emulsion (Fig. 13-1).

Fig. 13-1

Spray-dried polymer particle.

Over 90 % of all industrial manufactured polymer dispersions are produced by emulsion polymerization. The most important monomers, which are being used for applications in the building/construction industry, are vinyl acetate, ethylene, versatic acid esters, vinyl chloride, styrene and acrylics. Especially the use of ethylene as a co-monomer offers some extraordinary advantages: – environmentally safe, – no saponification, – UV-resistant (no yellowing), – very hydrophobic, – ideal for co-polymerization with vinyl acetate, – very low glass transition temperature, Tg, of –93 °C, – very flexible, and – good adhesion to most of the substrates. To guarantee the performance of a redispersible powder in its final application a protective colloid is added to the emulsion before the spraying process. The colloid protects the polymer particles from film forming during the spray drying process

13.2 Manufacturing of Redispersible Powders

331

and is also responsible for that the powder will redisperse in water again (Figs 13-2 and 13-3).
dispersion
particle concentration 69 ppm weight distribution curve 100 69 % ppm 80 60 40 20 0 0 2 4 6 1 1 particle size (diameter) 10 particle concentration

redispersion
particle concentration 92 ppm weight distribution curve 100 92 % ppm 80 60 40 20 0 0 2 4 6 1 1 particle size (diameter)
Fig. 13-2

particle concentration

10

Dispersion/redispersion – comparison of particle size distribution.

spray drying

adding water drying

dispersion
Fig. 13-3

protective colloid

redispersible powder

redispersion

The spray-dry process.

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13 Applications of Redispersible Powders

Over the years poly vinyl alcohol (abbreviated PVOH or PVAl) proofed to be the most preferred protective colloid for that purpose. In a cementitious environment PVOH will be partly saponified and also absorbed of fine particles within a mortar, i.e. cement and fillers. This results in a film forming of the dispersed polymer and finally the polymer film is not redispersible any more. Since the polymer film (acting as a binder) is distributed throughout the cement matrix it improves dramatically the adhesion, abrasion resistance, flexural strength, flexibility, water impermeability/water repellency (hydrophobicity) and workability of a cementitious system.

13.3

Dry Mortar Technology

The invention of redispersible powders by Wacker-Chemie in 1953 made for the first time the production of polymer modified dry mix mortars possible, which are nowadays referred to as one pack or one component system (“bagged” materials). New construction methods and building materials, which had the need for more safety, reliability, durability, efficiency and economy, have been achieved by using modern methods like the dry mix mortar technology. As a consequence worldwide the “jobsite mix technology” and the modification of mortars with liquid polymers on jobsites were and are substituted by polymer modified dry mix mortars. The product characteristics are very well adapted to the requirements of modern construction technologies, materials and climates. Pre-mixed and pre-packed dry mix mortars not only increase significantly the production performance and the productivity on construction sites, but guarantee also that high and constant quality binder, aggregates, and additives are being mixed exactly in the same ratio, thus ensuring a consistent high quality level within dry mix mortars. Furthermore, dry mix mortars offer solutions to specific problems that are precisely tailored to certain types of construction/material specifications. Especially in the USA, the legal aspect of a reliable, properly conducted construction job is very important to each manufacturer of construction materials. The use of redispersible powders and therefore also the use of polymer modified powdered mortars is already for many decades standard in the construction industry in Europe and North America (predominantly in the USA). Other marketplaces all over the world like South America, Asia, Africa and Australia are in the process following that example. More and more environmental reasons ask also for the usage of dry mortars, since the recycling of buckets becomes more and more an issue. Dry mortars are also easy to store, transport and do not require biocides. Typically dry mortar mixes contain the components listed in Tab. 13-1 and are defined according to German standard DIN 18557. The application areas of dry mix mortars are: – ceramic tile adhesive, – tile grouts, – E.I.F.S. (exterior insulation and finish systems)/E.T.I.C.S. (exterior thermal insulation compounds),

13.4 Markets and Application Areas of Redispersible Powders
Tab. 13-1

333

Dry mortar mixes. Aggregates fillers Polymer binder Additives

Mineral binders Portland cement (OPC) High Alumina Cement (HAC) Special cement Hydrated lime Gypsum, anhydrite

Silica sand Hydrated lime Dolomite sand Marble sand Lightweight fillers Special and functional fillers

Redispersible powder

Cellulose ether Pigment Defoamer Air-entraining agent Retarder Accelerator Thickener Hydrophobing agents Plasticizers

– – – – – – – – – – –

self-leveling over- and underlayments, screeds, stucco, skim coat, topcoat/finish coat, patch and repair mortar, adhesive mortars (for all kind of substrates), crack isolation membrane, powder paints, gypsum based compounds (joint fillers), waterproof membranes/sealant slurry, pool decking, and stamped concrete. The following paragraphs will describe the most important and most developed application areas for redispersible powders as they are ceramic tile adhesives/ tile grouts, thermal insulation systems (E.I.F.S.), self-leveling underlayments, patch and repair mortars, as well as water proof membranes (sealant slurries).

13.4

Markets and Application Areas of Redispersible Powders

To meet today’s technical requirements, almost all dry mix mortars require polymer modification. Many cementitious mortars contain cellulose ethers as an additive to improve water retention and workability. However, after setting and drying they will adhere poorly or not at all to most of the substrates used in modern construction technology such as polystyrene panels, fiber panels, wood panels, closed and non-absorbent substrates or old tiles. In addition, cementitious mortars are very hard, brittle and inflexible materials, whereas for many applications flexible and deformable cementitious materials are essential. As a consequence for almost all applications in modern construction, the modification of cementitious mortars with polymers is a must. In dry mix mortars the mineral binder, cement, and the polymer binder, redispersible powder, are ideal partners. The combination of both in a dry mix mortar

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13 Applications of Redispersible Powders

provides outstanding synergistic properties and characteristics, which cannot be achieved by either of the binders alone.
13.4.1

Adhesives for Ceramic Tiles

Ceramic tiles as well as natural stone were previously installed exclusively by using the thick bed mortar technique. Silica sand and cement were mixed together on the job-site, in order to produce a simple cement mortar with a cement/sand ratio of approximately 1:4 to 1:5. In some countries only cement is still used in order to set tiles. After having applied (“buttered”) the mortar at a thickness of 15 to 30 mm (0.6 to 1.2 inch) on the reverse side of the water-soaked or pre-wet tile, the tile is pressed into the pre-wet surface. The tiles have to be tapped to ensure uniformity and flatness of the tile surface, thus obtaining a final mortar bed of 10 to 25 mm (0.4 to 0.8 inch). This procedure causes not only compaction of the mortar, but leads in addition to the migration of the fine cement particles into the porous back side of the tiles and the porous substrate as well. This process assures the mechanical fixing of the tile in the mortar bed. This type of mortar has no slip resistance. Therefore tiling of a vertical substrate has to be started at the bottom and distance splinters become necessary. The described procedure shows very clearly that the thick bed method is a very time, cost and material consuming process. More significantly, there are technical restrictions using this technique. One of the examples is that only small, porous tiles can be applied over porous, solid and strong mineral surfaces. The application of tiles over wood would be almost impossible, since a mortar without any polymer modification would not only be not flexible enough to withstand the movement of a wood substrate over an extended period of time, it would also have no sufficient adhesion to the substrate. Consequently severe damage could occur and therefore the thin bed mortar technique has replaced the thick bed mortar technique in most industrial countries. It started in the USA in the early 1950s by adding a polymeric binder in form of a liquid latex dispersion to a job-site mixed mortar (see Chapter 8). Nowadays dry mix mortars modified with redispersible powders dominate this market segment more and more. After gauging the polymer modified dry mix mortar with water, it can be applied with a notched trowel, producing a ribbed mortar bed of uniform thickness. Due to the good water retention capacity of the thin bed mortar, neither the tiles nor the substrate have to be pre-wet. The tiles are pressed into the thin layered mortar with a slightly twisting movement of the tile. An anti-sag ceramic tile adhesive allows installing tiles on vertical substrates without using distance splinters between the tiles. The tile installer can also start from the top of the wall instead of the bottom. The mortar bed, which fixes the tiles, has a thickness of approximately 2 to 4 mm (up to 0.25 inch). Since this method clearly uses less material, it is more cost effective, can be used more universally; its execution is clearly simpler, faster and safer. The clear advantages of dry mix mortars modified with redispersible powders, which apply also for tile grouts, are:

13.4 Markets and Application Areas of Redispersible Powders

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– good workability, fast and easy to use, creamy consistency, – good water retention, which results in a long open time and good adjustability even at high temperatures, and – substantial anti-sag properties, if required. As far as the formulations for ceramic tile adhesives go there is a high variety of mortars offered in the market place in order to meet all the specific requirements. A major difference, for example, between Europe and the United States is the usage of wood as a substrate in the USA. Differences in the formulation are also determined by requirements of specifications or application circumstances like interior or exterior, wall tile or floor tile, vitrified tile or more porous tile, fast setting or regular setting, flexible or even highly flexible. The availability of certain raw materials i.e. silica sand determines very often how a formulation will perform. The two most important specifications worldwide are the European Norms “EN” and the American Standards ANSI 118.1-1999. The biggest difference between the two standards is the principal test setup. The European Standards require mostly tensile bond adhesion testing where else the American Standard uses shear bond testing. The other difference is clearly the storage conditions for the specimen before testing. A listing of both standards is shown in Tab. 13-2.
Tab. 13-2

EN and ANSI standards for CTAs.

European standards EN 12004 Definitions and specifications EN 1308 Anti-sag EN 1347 Wetting capability (coverage) EN 1346 Open time EN 1348 Tensile adhesion testing, including heat and freeze-thaw storage EN 1324 Shear-strength for mastics EN 12002 Deformability of cementitious CTA US standards ANSI A 118.4 ANSI A 118.11

Specifications for Latex Portland cement mortar Specifications for EGP (exterior glue plywood) Latex–Portland cement mortar

Cement-based standard tile adhesives can be classified in very simple (low quality) tile adhesives, which do not contain any polymeric binder. They do not meet European or American Standards. Such tile adhesives, providing a pure mechanical fixation can only be used for fixing small, very porous tiles. The substrate is supposed to be dimensionally stable, sound and solid as well as not showing any shrinkage or movement. If exposed to higher temperature or frost, there is a higher risk of failure. Non-modified mortars show for the most part no long-term performance. Simple tile adhesives have already a polymer modification of 1 to 1.5 % of a redispersible powder (calculated on total formulation). Such tile adhesives meet some parts of the mentioned national standards, but usually fulfill not all requirements. Only the usage of tiles with a medium porosity and small size could result in acceptable results with these types of adhesives.

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13 Applications of Redispersible Powders

Standard ceramic tile adhesives of good quality need approximately 1.5 to 3 % of redispersible powder on total dry mix. They meet the new European Norm for tile adhesives (mostly only C1 level) and pass also the ANSI specification 118.4 and 118.11. Larger formatted tiles can be applied with these materials over porous or less porous, dimensionally stable substrates. They are suitable for interior as well as exterior application. For standard applications these modified mortars provide higher quality security and a certain long-term stability, very much depending on the factors like climate conditions, weight traffic etc. Finally flexible (5 to 8 % of redispersible powder) and very flexible ceramic tile mortars with a polymer modification beyond 8 % up to even 25 %, guarantee the best performance over all, very good adhesion on all types of substrates with all types and sizes of tiles. These adhesives are used more universally and offer a much greater application variety, safety, as well as long-term durability and reliability. Nowadays these mortars are more and more used to fix the very popular highly vitrified tiles (water absorption <0.1 %) and natural stone tiles (like marble) in any format. The substrate can be non-porous and inorganic as well as wood. Even if the substrate still shows to a certain degree of shrinkage or expansion, including other types of movements or vibrations, these quality adhesives could be used to set tiles in a safe and durable way. Typical application examples for flexible ceramic tile mortars are: – floor heat system within the substrate, – to heat exposed surfaces, like i.e. tiles on a porch exposed to sunlight, – tiles over tiles, – over gypsum boards, – over backer boards, – over wood, – on water proof membranes, – on thermal and sound insulation panels, and – on light-weight concrete blocks. Tests conducted by international research and test institutes have proved that it is of high importance that cementitious adhesives provide a sufficient deformability and a certain degree of plasticity [1–4]. Only in that way, long-term durability and functionality can be guaranteed. Adhesive mortars have to be able to absorb stresses that occur between two materials as tiles and substrate in order to prevent damages. Typical damages are cracking or even delaminating of the tiles. Irreversible differential movement, such as shrinkage causes always stress between tile and substrate (fresh concrete is always likely to shrink). Reversible movements of the substrate like vibrations and thermal movements due to heat or cold are also sources of stress between substrate, adhesive and tile. The different modulus of elasticity of tiles and substrate is also enhancing the stress within a ceramic tile mortar (Fig. 13-4). European Norm EN 1348 addresses this issue in a heat test as well as in a freeze/ thaw test. Shear stress between substrate and tile normally concentrates in the peripheral zones of a tile. That means, the bigger the tile the higher the flexibility of the adhesive has to be in order to avoid cracking or delaminating of the tile. The flexibility (deformation capability) of a ceramic tile adhesive depends on the polymer/cement ratio. It is one of the two most important ratios to be determined in a ceramic

13.4 Markets and Application Areas of Redispersible Powders

337

tiles

tiles

deformable adhesive mortar
substrate eg. concrete substrate eg. concrete

initial dimension

initial dimension

shrinkage of substrate eg. shrinkage of concrete

expansion of tiles eg. thermal expansion

tiles

tiles

rigid, non-deformable adhesive mortar
substratre eg. concrete substrate eg. concrete

initial dimension

initial dimension

Fig. 13-4

The stress between substrate and tile.

tile mortar (the other one is the water/cement ratio). The German test DIN 18156/3, as well as EN 12002, measures the flexibility of ceramic tile adhesives. As a result of these tests it can clearly be shown, that the higher the polymer/cement ratio the higher the flexibility of a mortar system (Fig. 13-5).

Fig. 13-5

The flexibility of ceramic tile adhesives.

It is very important to mention that the deformation capability of a given cementitious system also depends to a large extent on the degree of hydration of the cement. Consequently, the flexibility of different adhesives can only be compared at identical

338

13 Applications of Redispersible Powders

degrees of hydration of the cement. Unfortunately this is very often not considered within the storage conditions of different standards, that deal with the testing of flexibility (Fig. 13-6).
16.0 14.0 12.0 Flexion/deformation [mm] 10.0 8.0 6.0 4.0 2.0 0.0 50% Portland Cement 40% Portland Cement 35% Portland Cement 30% Portland Cement

Traverse deformation test according to EN 12002 - 5% polymer modification at different cement levels
standard conditions water storage (full hydration) 7d sc/ 14d in water/ 21d sc

Fig. 13-6

EN 12002 results on flexibility.

The relative humidity of approximately 95 % at the beginning is not kept constant during storage and is not sufficient for a full hydration of the cement. Over the time cementitious adhesives will reach their full hydration thus resulting in sometimes very low flexibility of the mortar. For example, the use of additives and/or polymers with a strong retardation effect on the cement will cause an incomplete hydration of the cement and will lead temporarily to a higher polymer-to-cement ratio. The flexibility measured at this point will not reflect the real flexibility of the system after full hydration of the cement phase. After complete hydration of the cement, “soft” polymers (lower glass transition temperature, Tg) will perform at an appropriate dosage level better compared to polymers with a higher Tg, especially if used and tested at lower temperatures (Fig. 13-7). (The glass transition temperature describes the flexibility of a polymer. The “rule of thumb” is the lower the Tg the higher the flexibility. Tg is determined from the ratio of different monomers and their individual Tg in a polymer, by use of the Fox equation [5]). The adhesion of tiles to the substrate is certainly as important for a ceramic tile adhesive as the flexibility. The European Norm uses a “pull off test” to determine the adhesion, where as the US standard ANSI 118.1 – 1999 prefers the shear bond test. A simple ceramic tile mortar with no polymer modification will fail in the adhesion test especially after heat aging or over wood (ANSI 118.11 – 1999). The same mortar modified with only 2 % of redispersible powder will pass both tests. With the pull-off

13.4 Markets and Application Areas of Redispersible Powders

339

Fig. 13-7

Flexibility at lower temperatures.

test, it can be demonstrated that a ceramic tile adhesive without polymer or with a low polymer level will only be able to pass, if wall tiles (very porous, high absorptive tiles) are used. In addition, it can be demonstrated that only a sufficient amount of redispersible powder provides a significant adhesion on critical substrates like PVC, wood or tiles (Fig. 13-8). A sufficient high polymer modification of the ceramic tile adhesive is necessary especially when non-porous, highly vitrified tiles (low to no water absorption) are used. In this case, there will be no mechanical anchoring like described earlier for porous tiles. The redispersible powder (chemical bonding), in this case, only provides the adhesion. This is, besides the outlined reasons for sufficient flexibility, another important factor for a higher polymer modification. A ceramic tile adhesive that performs very well over almost all substrates, with all types of tiles (size, water absorption) should contain at least 6 % of redispersible powder and the cement content should be limited to 30 to 35 %. An adhesive formulation that considers these two important components at the right amount is very likely to pass all international standards. However, in an adhesive formulation has more to be considered than only the polymer and cement level.

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Fig. 13-8

Adhesion of ceramic tile adhesives to different substrates.

13.4.2

Tile Grouts

Tile grouts, which are used to fill the joints in between the tiles, are very similar to ceramic tile adhesives in their formulations. They are expected to be water repellent (hydrophobic), to have good adhesion to the substrate and the edges of the tile, sufficient hardness, a low tendency for staining, cohesion strength, abrasion resistance and flexibility. In the USA the field of tile grouts is much more diversified than, for example, in Germany, because US manufacturers offer a much greater variety of colors. Therefore, color consistency is of high importance as well. Redispersible powders with a hydrophobic effect are normally used to achieve all requirements of a tile grout. They reduce the risk of efflorescence as well as staining of the grout. The standards in the US and Europe are summarized in Tab. 13-3. The fields of ceramic tile mortars and tile grouts are certainly the most developed for redispersible powders in cementitious applications. The use of redispersible powder improves adhesion bond strength to all types of substrates, the deformability (flexibility), the cohesive and flexural strength, the open time the wetting capability as well as the workability within dry mix mortars.

13.4 Markets and Application Areas of Redispersible Powders
Tab. 13-3

341

EN and ANSI standards for tile grouts.

European standards* EN 12808-1 Determination of chemical resistance EN 12808-2 Determination of abrasion resistance EN 12808-3 Determination of flexural and compressive strength EN 12808-4 Determination of shrinkage EN 12808-5 Determination of water absorption EN 12002 Determination of deformability US standards ANSI A 118.6 ANSI A 118.7
* There

Specification for standard cement grouts for tile installation Specifications for polymer modified cement grouts for tile installation

is also a draft of “Tile grout mortars for tiles, definitions and requirements”

13.4.3

Exterior Insulation and Finish Systems and Top Coats

With the beginning of the 1970s exterior insulation and finish systems (E.I.F.S) were used in Germany. (E.I.F.S. is predominantly used in North America. The abbreviation used in Europe is ETICS – exterior thermal insulation compounds.) The first oil crisis in Germany 1973 together with financial support of the government for homeowners had helped tremendously to promote the system. Some of the advantages of E.I.F.S. are saving energy, healthier climate condition inside the house, less damages of facades and possible savings at the over all building costs. Between 1973 and 1993 approximately 300 million square meters of E.I.F.S. were applied on facades in Germany. As a consequence more than 18 billion liters of oil were saved (approximately 113 million barrels). This also means considerably less CO2 was released into the atmosphere, that also emphasizing a positive environmental aspect of E.I.F.S. After Germany, the country with the most usage of E.I.F.S. is the United States. However, the use of E.I.F.S. in the past within the United States has been more for optical reason. Recently more and more the energy saving aspect of the system has become a more considered aspect for homeowners. In both countries, organizations exist representing the E.I.F.S. industry and its interest: representative of Germany is the “Fachverband Waermedaemm-Verbundsysteme” and of the USA the “Exterior Insulation Manufacturer Association, EIMA”. The technology used in both countries is predominantly based on the usage of polystyrene as an insulating material. In the early 1970s, the materials for E.I.F.S. offered in Germany were shipped to a construction site as ready to use systems (pasty consistency). They had to be mixed with cement before usage. Mistakes occurred by not meeting the polymer cement ratio according to the manufacturers’ requirement, resulting in damages and complaints. The industry shifted almost completely to dry mix systems in order to avoid the mentioned problems. The use of machines also promoted dry mix mortars modified with redispersible powders. The time and cost savings remain tremendous. In the US, reliability and control over the formulation out of production as well as time and cost savings of machine applicable systems,

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13 Applications of Redispersible Powders

has clearly set the trend over the last 5–10 years towards more and more usage of the dry mortar technology and, therefore, towards redispersible powders/polymers. Because of the use of redispersible powders, the application of E.I.F.S. has reached such a high level of reliability and quality consistency that manufacturers in Germany normally allow a 30-year warranty for their systems. So far this level of warranty is not yet achieved in the US. In Europe, as well as in the US several technical tests are conducted in order to prove the performance of E.I.F.S. under different test conditions. The testing of such systems is very severe. Some of the most important types of tests conducted on an E.I.F. system are: – stability and flammability, – insulation properties, – adhesion of cementitious materials on polystyrene, – water absorption, – impact resistance, and – flexural and compressive strength. Most of the tests are still very much depending on the country (Europe). In the US there are different authorities (regional and city codes) like the “American Society for Testing and Materials – ASTM”, the “Building Officials and Code Administrators – BOCA”, the “International Conference of Building Officials – ICBO” and the “Southern Building Code Congress – SBCC”. Information on test procedures is also available through EIMA. More specific information can be gathered through the different organizations. In Europe the entire E.I.F. system needs even a technical approval granted by testing institutes according to the “European Organization for Technical Approval, EOTA”. The principle layers of an E.I.F. system are shown in Fig. 13-9.

1. Substrate 2. EPS-Adhesive 3. EPS-Board 4. Base Coat 5. Top Coat/Finish

Fig. 13-9 The principle structure of an E.I.F. system.

Substrates might vary. In the US it is normally plywood. Normally one will find concrete/brick as a substrate. Right on top of the substrate the insulation board is glued with an adhesive. In addition sometimes mechanical fasteners are use as well.

13.4 Markets and Application Areas of Redispersible Powders

343

85 % of the insulation material used in Germany is Extruded Polystyrene “EPS”. The EPS adhesive is normally the same material as the base coat. The functionality of the base coat is protection and reinforcement of the EPS panel. Without polymer modification there would be no adhesion of the EPS to the substrate and no adhesion of the base coat to the EPS panel. Besides adhesion, the right polymer modification becomes also very important when impact resistance, water absorption or deformation capability (flexibility) is tested. The base coat has an important functionality within the entire system. The right modification of the base coat with at least 3 to 6 % redispersible powder will finally guarantee good performance values and as a consequence contribute to an excellent weather stability of the entire system. The integrity of the base coat, meaning a crack free base coat, is a precondition for good technical performance. For that purpose the polymer-to-cement ratio should be as high as possible. This is one of the main differences between Europe and US . Normally the cement content in US systems is higher than in Europe. Assuming the polymer content is very similar, this results in a higher polymer-to-cement ratio in European systems compared to US systems. This has to do with the fact that the preference in Europe is towards more flexible system where else in the US a hard surface appearance of the base coat is preferred by contractors. Certainly as important as the base coat is the topcoat for the entire system. Here we find probably the biggest difference between, for example, Germany and the United States. In the US cementitious topcoats are almost not used at all. They are synthetic, cement free systems that are very often ready to use and based on emulsion technology. In Europe, as with Germany, topcoats are cement based as well. Top/finish coats must meet certain critical physical and technical requirements. These include: – good adhesion to the substrate (tensile adhesion strength), – low water absorption or water repellency (hydrophobicity), – good drying characteristic (high water vapor permeability), – low susceptibility to cracking (good relaxation properties, flexibility), – the modulus of elasticity of the top coat should be lower than the modulus of elasticity of the substrate (layer below), – resistance to weathering, – mechanical stability (high impact resistance), – low dirt pick up, – very low flammability. (Finish or topcoats can also be named render, plaster or stucco. Normally slight differences apply, for example in thickness of the coating depending on the technology used. As far as the use of redispersible powder is concerned, they can be considered equivalent.) The addition of organic polymeric binders in form of redispersible powders to mineral plasters and stuccos can significantly enhance certain properties, such as adhesion to the substrate, mechanical resistance, low water absorption (hydrophobic effect by using special redispersible powders) and long-term durability. In order to meet these requirements the preferred redispersible powders used in topcoats are vinyl acetate/ethylene copolymers. Especially when it comes to flammability vinyl

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13 Applications of Redispersible Powders

chloride containing systems perform the best closely followed by vinyl acetate ethylene containing polymers. Topcoats/E.I.F.S based on acrylics and acrylates, like styrene acrylics, perform the worst in this respect. The addition of approximately 0.5 to 2 % special hydrophobic redispersible powders to dry mortars additionally imparts uniform water repellency throughout without effecting the water vapor permeability. Mineral topcoats are composed of lime and cement as mineral binders, aggregates (fillers like silica sand), pigments and additives, such as cellulose ethers, starch ethers, lightweight fillers, fibers, thickener, hydrophobic agents, wetting agents and sometimes even surfactants. With the exception of any mineral binder this list applies also to synthetic topcoat which are almost exclusively used in the US. Table 13-4 shows some of the specifications for topcoats in Europe (Germany) and the US.
Tab. 13-4

Specifications for topcoats.

German-US standards DIN 18555/ASTM C 109 DIN 18555-6/* DIN 52617/ASTM C 413 DIN 52615/ASTM E 96 DIN 18555/ASTM C 231 DIN/EN 196/ASTM C 580
* ASTM

Compressive strength Tensile bond adhesion Water absorption Water-vapor permeability Air content Flexural strength

E 2134-01 for E.I.F.S.

One aspect that is very important to the E.I.F.S. industry as well as to topcoat manufacturers is certainly the hydrophobicity of their base coats and/or topcoats. What is the mechanism behind a hydrophobic effect achieved by using a hydrophobic redispersible powder? When water is added to the dry mix topcoat, the polymeric binder in the form of a redispersible powder is very quickly redispersed. Then the polymer particles accumulate mainly in the pores, forming a film that coats the pores without actually blocking them [6–8]. Because the pores (capillaries) are coated with a water repellent polymer film with good adhesion to the cement, the capillary water absorption is reduced. Thus a permanent effect is achieved throughout the mortar. If the amount of redispersible powder stays within 3 to 6 % there is no loss of water vapor permeability. This, of course, depends also very much on the hydrophobicity of the used redispersible powder. Because of the mentioned adhesion of the polymer to the cement pores the adhesion as well as the flexural strength and toughness of the material is improved also. Scanning electron micrographs are shown in Fig. 13-10 and demonstrate the formation of the polymer film within the cement matrix. The SEM technology was also used to demonstrate that the redispersible powders continue to fulfil their functionality over an extended period of time. This is also shown by experiments to determine physical factors such as water absorption and water vapor permeability on defined test specimen after long-term exposure to outdoor weathering conditions. Figure 13-11 shows the capillary water absorption of test specimen after up to 6 years outdoor exposure at different polymer levels.

13.4 Markets and Application Areas of Redispersible Powders
Fig. 13-10 SEM of polymer film in cement matrix.

345

Capillary water absorption of mineral topcoat - long term exposure 4 3.5
water absorption coefficient according to DIN 52617

3 2.5 2 1.5 1 0.5 0 0.5% 1.0% 2.0% 3.0% 3.5%
percentage redispersible powder on total formulation

21 days standard conditions

1 year outdoor exposure

6 years outdoor exposure

Fig. 13-11

Long-term performance of cementitious topcoats.

13.4.4

Self-leveling Underlayments

The area of self-leveling underlayments (SLU) is out of a technical perspective probably the most complex one if it comes to applications of redispersible powders. On a given uneven substrate (i.e. screed or surface to be refurbished), self-leveling mortars have to provide a suitable, smooth and solid substrate in order to apply all kind of flooring materials like carpets, wood parquet, PVC, tiles etc. Self-leveling underlayments should be applicable in an easy and efficient manner, even for large areas.

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13 Applications of Redispersible Powders

Therefore, the SLU material has to have very good flow characteristics, self-leveling and self-smoothing properties. In addition, it should perform fast setting/drying, saving time and thus the floor surface can be applied after only a few hours. The SLU material should adhere to all kind of substrates, provide low shrinkage, high compressive strength and abrasion resistance. The technical requirement of a SLU reaches from very simple to highly sophisticated products. They vary in thickness from a very thin layer of 1–10 mm (1/25–2/5 inch) (feather finish, self-leveling/troweling mortars and underlayments), up to 60 mm (approx. 2.5 inch) for self-leveling screeds, which are always applied by machines (mixing and pumping in one set up). The set time (“walk over time”) of these materials changes from normal/regular setting to very fast setting products. Normally this is a question of the requirement of a specific job, allowing putting down the floor above the SLU in a certain time frame. The shorter the setting/drying time, the thicker the mortar is applied, the more complicated and expensive the formulation becomes. Self-leveling compounds (underlayments and screeds) are based on special hydraulic binders like Portland cement (OPC), high alumina cement (HAC) and gypsum (anhydrite), in order to achieve fast curing and drying by avoiding excessive shrinkage or expansion. So far there are no standards on self-leveling underlayments (SLU) in Europe or the U.S. However, the techniques and the application is very well known for many years. Polymer modification is absolutely necessary within this technology, since the requirements are very sophisticated. According to their use and the specific requirements, SLUs are polymer modified by 1–10 % of redispersible powder calculated on total formulation. Standard products are normally modified between 2 and 4 %, highly modified mortars are mainly used for refurbishment of wooden floorings with self-leveling compounds. The redispersible powder increases the adhesion to all kind of substrates, decreases the internal stresses (reduced crack formation and high abrasion resistance), improves the flexural strength, elasticity and the abrasion resistance. Special powder grades will also support the self-leveling and self-flowing characteristics of the mortar. Figure 13-12 shows the results of an abrasion test for a self-leveling compound with and without modification with a redispersible powder. Depending on the dosage of the redispersible powder, the abrasion resistance can be reduced significantly. This becomes especially than very interesting, when the SLU is also used as a wearing surface in an overlayment application.
13.4.5

Patch and Repair Mortars

Concrete is a very versatile, long-lasting and durable building and construction material if it is applied according to the state of the art. In the past, and even today, unfortunately, repeated disregard of the fundamental principles of concrete and structural concrete application has lead, and, in many cases, still leads to severe and serious damage in the building industry. The cost of the repair of concrete structures has dramatically increased over the last 30 years in all industrial countries. In Ger-

13.4 Markets and Application Areas of Redispersible Powders

347

Fig. 13-12

Abrasion resistance with and without redispersible powder.

many approximately 20 % of the cost of the volume of structural concrete work is attributed to the repair and maintenance of existing buildings and structures. The degradation of structural concrete is caused by corrosion of the steel reinforcement due to chemical processes, which often occur over a long period of time. One of the main reasons is the carbonation of concrete. Acidic carbon dioxide (CO2) from the atmosphere and other aggressive media (such as SO2, acid rain) neutralizes the alkalinity of the concrete. Once the alkaline environment of the steel reinforcing no longer exists, the steel starts to corrode and, due to its volume increase, causes splitting of the concrete on top of the steel reinforcement. A secondary cause of corrosion is the penetration of free chloride ions into the concrete, leading to chloride ion attack on the steel.

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13 Applications of Redispersible Powders

In the construction industry concrete repair work can be classified in two types: – concrete repair, which does not contain steel reinforcement and which does not have load-bearing functions. The repair is normally done for aesthetic reasons (cosmetic repair work) only, with namely patching mortars/compounds – repair and reconstruction of damaged reinforced and load-bearing concrete structures, in order to maintain and reconstitute their structural stability. This is done in stages with different kind of mortars, which are part of a “concrete rehabilitation system” (typical applications: repair work and rehabilitation of bridges, parking decks, tunnels, etc). Patching mortars for re-profiling and cosmetic repair are mainly based on dry mix mortars and are not part of an entire repair or rehabilitation system. Usually, cement-based mortars are used for indoor and outdoor applications, whereas gypsumbased products are only used for some specific indoor applications (cosmetic repair). Patching mortars are used to repair defective or damaged areas of mineral surfaces without taking on a load bearing function, i.e. for filling small holes, voids, cracks and cavities in order to restore the original dimension. Typical applications are patching mortars for walls, ceilings, floors, steps of staircases, etc. These mortars must have the following characteristics: – good workability, – easy to apply, – good adhesion to all construction substrates, – high durability and abrasion/wear resistance, if exposed to direct wear/load, – sufficient flexibility to reduce the risk of crack formation, – low shrinkage, and – water repellence for outdoor applications. To meet the required technical criteria, these patching mortars are applied as a polymer modified pre-packed dry mix mortar. Polymer modification with redispersible powder will – depending on the dosage – improve the: – workability of the mortar, – wetting capability of the substrate, – adhesion to all kind of substrates, – flexural strength, – abrasion resistance, – flexibility (lower modulus of elasticity than substrate), – durability, and – water repellent effect by using special grades of hydrophobic redispersible powders. To be able to guarantee the durable and reliable repair of structural concrete, three main fundamental requirements of a concrete rehabilitation system must be fulfilled simultaneously: – restoration of the corrosion protection of the steel reinforcement (alkaline environment), – restoration and re-profiling of the concrete structure including its load-bearing functions, and

13.4 Markets and Application Areas of Redispersible Powders

349

– restoration of the durability of the whole construction (protection against weathering and environmental damage caused by CO2, SO2, Cl2, salts, etc.). Today, polymer modified cement concrete (PCC) mortars, which can be applied by hand, in a wet or even a dry spraying process, are usually used for the rehabilitation of concrete structures. Different kind of mortars with different characteristics and functions are used as the components for concrete rehabilitation systems: – primer and adhesion promoter for the reinforced steel (polymer modified cementitious slurry or epoxy based coating materials), – adhesion promoter slurry (primer or key-coat) for the concrete to be repaired (polymer modified cement based slurry), – restoration and re-profiling mortar (polymer modified cement based mortar), – fine stopper or smoothing mortar (polymer modified cement based mortar containing fine aggregate), and – protection and finish coat (dispersion paints, crack over bridging paints, cementitious waterproofing sealing slurries, etc.). The improvement of adhesion to concrete and steel, using a polymer modified reprofiling mortar, with and without applying a cementitious primer, is demonstrated in Fig. 13-13; Fig. 13-14 shows the improvement in flexural strength of a typical reprofiling mortar applied by hand with and without different grades of redispersible powder.
Tensile bond adhesion after 28 d standard conditions polymer/cement ratio = 0.07 3

2.5 Tensile adhesion [N/mm2 ]

2

1.5

1

0.5

0 over concrete without primer with primer over steel

Fig. 13-13

Adhesion to concrete and steel with and without primer.

The flexural strength of the mortar is already significantly improved by adding only 2 % of redispersible powder without affecting the compressive strength too much.

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13 Applications of Redispersible Powders

Flexural strength of repair systems modified with different redispersible powders and applied by different techniques
14 12

Flexural Strength [N/mm2 ]

10 8 6 4 2 0 shotcrete spray applied no polymer redispersible powder 1 hand applied redispersible powder 2 redispersible powder 3

Fig. 13-14

Flexural strength improvement by use of redispersible powders.

Almost the same improvements are obtained by applying the repair mortar through a dry shotcrete process. Within this process the water is mixed with the dry mortar only in the jet. After that the mixed mortar is immediately sprayed onto the surface. Despite this extremely short mixing and almost no slake time, the redispersible powder redisperses quickly and completely enough in order to improve the tensile adhesion strength and the flexural strength in almost the same magnitude compared to a conventional application by hand.
13.4.6

Waterproof Membranes

Water in liquid or in vapor form is the most destructive weathering element for building constructions, like concrete, masonry, and natural stone structures. Waterproofing and damp-proofing techniques are used to preserve a structure’s integrity, functionality and usage throughout its lifetime. For preventing all possible water intrusions, the exterior of a building has to be protected form top to bottom with waterproofing materials. Exterior parts of a building could be classified in roof coating, below-grade waterproofing materials, which are materials to prevent surface- and ground water or water under hydrostatic pressure from entering into a structure. Typically metal and plastic films, cementitious waterproofing sealing slurries and bituminous waterproofing systems are used for that type of application. Above-grade waterproofing materials, which prevent water intrusion into exposed structure elements, could be categorized into:

13.4 Markets and Application Areas of Redispersible Powders

351

– decorative and finishing barrier systems, i.e. all kinds of paints; – mineral topcoats (renders, plasters); – damp-proofing materials, which reduce or prevent water vapor transmission through building materials and are not subjected to weathering or water pressure (water vapor barrier foils); and – flashings, materials or systems installed to direct water entering through the wall cladding back to the exterior like metal foils in walls to prevent capillary water uptake. All waterproofing has to be part of a whole system and must interact integrally to reach complete effectiveness and to prevent water infiltration. In case one of these system parts fails or does not perform with all other protection systems, leakage will occur. Adequately controlling groundwater, rainwater and surface water, as well as the transport of humidity in the form of water vapor will avoid unnecessary repairs to building’s exterior or its damage or even destruction (deterioration). Apart from protecting the exterior of building constructions, there is a multiplicity of waterproofing materials for interior use. Some of the waterproofing materials are used to protect against the detrimental action of aggressive substances like salts and acids transported by the water. Traditional sealing and waterproofing systems, i.e. according to the German standard DIN 18195, include bituminous materials, plastic waterproofing foils and metal tapes for interior and exterior applications. Different types of materials can be used in order to seal and protect the surface of buildings or its structural components against the intrusion of dampness and water. Nowadays products for that purpose are based on reactive resins like epoxy and/or polyurethane, dispersions (paintable waterproofing membranes) and mineral binders like cement, which are known as waterproofing membranes or sealant slurries. Cementitious waterproofing membranes have been successfully used for more than 40 years in Europe for protection of a wide range of building structures and structural components. The structures were either exposed to periodically or longterm wettings (surface water, seepage water), low hydrostatic pressure (soil dampness) or in combination with appropriate engineering even high hydrostatic pressure. Cementitious membranes (slurries) are used to waterproof wet rooms and water tanks, and due to their excellent weathering resistance they are also used for exterior surface protection. Further typical applications are the sealing and waterproofing of basement walls, swimming pools, walls and floors, in bathrooms, on balconies and porches (as a waterproofing layer to be tiled over). Especially in the case of a tile application these slurries can also act as crack isolation membranes. In addition, flexible, cementitious waterproofing membranes are often used as a protective surface-coating system for structural concrete (i.e. protection of reinforced structural concrete within new structures as well as for concrete structures after restoration). It is applied for the protection against penetration of water, chlorides and free carbon dioxide in order to avoid corrosion of the reinforcing metal and can provide a protective layer to a building against aggressive chemicals (sulfates, acids, i.e. in waste-water drains). Some of the advantages of cement-based waterproofing membranes are:

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13 Applications of Redispersible Powders

– – – – –

excellent resistance against water, even if exposed permanently; excellent resistance against long term weathering; good scratch resistance; good load-carrying capacity; and much higher water vapor permeability compared to most of the other systems. Consequently there are no problems with blistering since water vapor passes through the membrane. Cement-based waterproofing slurries are easy to use, non toxic, provide a fully bound and monolithic surface without joints and can be easily applied on substrates with complex surface shapes. In contrast to other systems, cementitious waterproofing slurries can even be used on damp and wet mineral surfaces. Their physical properties are also less temperature dependent compared to bitumen based materials. Simple, non-polymer modified cement based slurries are still used for the protection against surface water, but they are not suitable to seal against water under hydrostatic pressure. In order to improve the poor adhesion, the poor water tightness, and the extremely low deformability or flexibility of these non modified systems, polymers are added in form of liquid dispersions on the job-site or in form of a redispersible powder already mixed in the dry mix mortar. The use of special additives in the dry mix mortars like water retention agents, thickening agents and rheological additives in combination with the polymeric binder, the redispersible powder, provide an excellent workability and make sure that there is no need for a post watertreatment of the applied slurry. Today, in principle, two different systems of cementitious waterproofing membranes or slurries are available: 1. Standard or rigid mineral waterproofing slurries, which are polymer-modified, pre-packed dry mix mortars containing approx. 3 to 6 % of redispersible powder. They are used for mineral substrates, which are stable, sound and solid. There should be no risk for crack formation, movements or dimensional changes like shrinkage. 2. Flexible and highly flexible cementitious waterproofing slurries (as two-component or one-component systems). In addition to the traditional, rigid waterproof membranes, developments in the late 1970s led in Europe to flexible waterproofing slurries, which are to a certain extend capable to over-bridge small cracks (up to approx. 1 mm) in the substrate. The flexibility of such products strongly depends on the polymer/cement ratio and certainly also on the flexibility of the polymer itself. Flexible and highly flexible waterproofing cementitious slurries are used on substrates still undergoing shrinkage, vibrations, movements, stresses, crack formation and on substrates difficult to be coated like wood, steel, aerated light weight blocks and gypsum. Due to their high polymer content (up to 25–40 % on total formulation), they are diffusion and chemically resistant against chloride, sulfate ions and carbon dioxide or other aggressive materials. Thus far these flexible cement based waterproofing, sealing slurries have been mainly used as two-component systems (liquid dispersion/emulsion added to the

13.5 Summary

353

pre-packed dry mix). But due to the many disadvantages of modifying mortars with liquid dispersions on a job-site, in modern construction technique more and more the one-component, flexible cementitious slurries, modified with high dosages of special redispersible powders are used. These one-component, premixed polymermodified dry mix mortars are offering advantages as they were already discussed within this chapter.

13.5

Summary

The need for new construction methods and building materials, that are safely, reliably, efficiently and economically to apply, promotes modern technologies like the “dry mix mortar technology”. Redispersible powders make the production of complete pre-manufactured high quality mortars (“bagged mortars”) possible. As a consequence, job-site mix technology and job-site modification of mortars with liquid polymers is being replaced all over the world. Especially since product characteristics can be specifically designed for modern construction requirements and climate conditions by using dry mix mortars. Dry mix mortars modified with redispersible powders provide a significantly improved productivity on the construction site. They allow a high degree of rationalization coupled with an easy, rapid, more efficient and safer handling and processing of the product. This eliminates onsite mixing errors and ensures, consistently, excellent results. The quality of the workmanship is consistent on a high level thus improving the warranty status of a construction job dramatically. Dry mix mortars, mainly based on cement but also on gypsum, that are modified with redispersible powders have been successfully used for many decades all over the world. The most typical applications are: – ceramic tile adhesives, – tile grout mortars, – mortars for the thermal insulation systems, – stuccos, skim-coats and finishing renders, – patch and repair mortars, – self-leveling under- and overlayments, – waterproofing sealing slurries (membranes), – joint compounds, and – powder paints. The modification of dry mix mortars with dry polymers in the form of redispersible powders also significantly improves the technical performance of the mortars. The combination of the mineral binder with a polymeric binder in the form of an redispersible powder in dry mix mortars guarantees outstanding synergistic properties and characteristics, which cannot be achieved by either of the binders alone. The sufficient modification of mineral dry mix mortars by redispersible powders will improve workability, adhesion to various substrates, flexibility and deformability of

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13 Applications of Redispersible Powders

the mortars, abrasion resistance, density (impermeability), flexural and cohesive strength and the long-term durability. Manufacturers, contractors, applicators and end-users (“Do it yourself” market) all benefit significantly from dry mix mortars modified with redispersible powders. That technology almost exclusively makes machine applications, which become more and more popular with all kinds of construction materials, possible.

References
1 Research report No. 13 of “Vereinigung 4 Rapport “Lim for keramiske fliser;

von Systembouwers van de Werkgroep SA 5, Tegels, Het vermijden van Schade aan gelijmd Wandtegelwerk”; March 1975, Vereinigung von Systembouwers, Gravenhage, Netherlands. 2 Publications of G. Wesseling (TNO Institute, Netherlands); in Tonindustrie Zeitung No. 8 1971, 95, 211. 3 Research report B II 5 – 800177-118; “Ermittlung des Verformungsverhaltens von Duennbettmoerteln bzw. Klebstoffen fuer keramische Fliesen”; August 1979 von Prof. Dr. Kirtschig; Technische Universitaet Hannover.

5 6 7 8

methode for proving av even tile aoverfore relative bewegelser mellom underlag og fliser (flexksibilitet)” von BYGGFORSK, Norwegisches Bauforschungsinstitut, Forskningsveien 3 b; Postboks 123 Blindern, 0314 Oslo 3, Projekte E 3593, Trondheim 04/08/1992. Fox T.J.; Bull. Am. Phys. Soc. 1956, 1, 23. Schulze, J.; Tonindustrie-Zeitung 1985, 109, 698. Schulze, J.; Beton 1991, 5, 232. Adler, K.; Schweizer Baublatt 1988, 31, 44.