MODIFICATION WITH REDISPERSIBLE POLYMER POWDERS

The principle of modification of cement mortar and concrete with redispersible polymer powders is almost the same as that of latex modification except that it involves the addition of redispersible polymer powders. Mostly the redispersible polymer powders are used by dry mixing with the cement and aggregate premixtures, followed by wet mixing them with water. During the wet mixing, the redispersible polymer powders are reemulsified in the modified mortar and concrete, and behave in the same manner as the latexes for cement modifiers. 

The invention of redispersible powders by Wacker-Chemie in 195 3 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 job-site mix technology and the modification of mortars with liquid polymers on job-sites 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 cHmates. 

The adhesion of tiles to the substrate is certainly as important for a ceramic tile adhesive as the flexibihty. 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 puD-off... 

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 wiU improve workability, adhesion to various substrates, flexibility and deformability of... 

To meet today s technical requirements, almost aU dry mix mortars require polymer modification. Many cementitious mortars contain cellulose ethers as an additive to improve water retention and workabihty. However, after setting and drying they wiU 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 apphcations flexible and deformable cementitious materials are essentiaL As a consequence for almost all apphcations 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... 

Simple tile adhesives have aheady 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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