Revised April 19, 2006
Use of Latex or Emulsion Additives with Portland Cement-Based Mortars & Grouts
Polymers are organic compound substances, natural or synthetic, made of many repeating chemical units called monomers. While the term “polymer” can be applied to a wide range of plastics or elastomers, in this bulletin we will focus on the narrow group of synthetic polymers that are made as polymer dispersions in an aqueous phase (solids polymer particles suspended in water). These solid polymer particles come in liquid dispersion form, referred to as emulsion or latex, or in dry form, referred to as redispersible powder polymer.
These polymers are further defined by their actual chemical make-up (which monomers were used). If a single monomer unit is used, the resulting polymer is a homopolymer. If two different monomers are involved, a copolymer is obtained. If three different monomers, terpolymer; and so on.
Copolymers are the most common types of polymers being used as additives in Portland cement based mortars and grouts. They are: Acrylate copolymers (acrylic), Styrene Butadiene Rubber copolymers (SBR), and Vinyl Acetate-Ethylene copolymers (VAE). While all have their pros and cons, manufacturers select a polymer that best meets the needs of the application and meets the specifications of the industry.
Once mixed in a Portland cement mortar, the water is used in hydration of the Portland cement or leaves the system (evaporation, etc.). As the water leaves, the polymer particles coalesce to form a continuous film that imparts specific properties to Portland cement products.
Polymer additives are recommended for use with Portland cement mortars and grouts for the following reasons:
1.Adhesion is improved on all substrates. This is particularly important on hard, smooth surfaces such as vitreous (porcelain) and semi-vitreous tiles, glass mosaics, marble, pavers and quarry tile. Mortars need polymer to bond to wood and other difficult to bond to substrates.
2.Internal cohesion is increased in Portland cement mortars and grouts. The tensile and flexural strength is increased.
3.Workability is improved in Portland cement based thin-set mortars and grouts.
4.Water demand is reduced, thus improving water to cement ratio without hurting the workability. This also lends to increasing the density of the mortars and grouts. Grout’s resistance to staining is improved by making the resulting product denser, and thus easier to clean and maintain.
5.Freeze/Thaw resistance is improved. Permeability of mortars is reduced due to film forming properties of the polymer. Also, the tensile and flexural strength is stronger to help resist failure due to movement.
6.Color retention and uniformity in grouts is significantly improved.
7.Impact and abrasion resistance is greatly improved in mortars and grouts by polymer addition.
8.Polymer reinforced grouts are excellent for grouting tiles with high absorption levels. Tiles with an absorption rate over 7% (soft bisque wall tiles) tend to pull the water out of conventionally mixed grout prematurely. Polymers can help combat this problem.
Research data from the Portland cement Association, as well as the basic suppliers of the polymers, support the above recommendations.
MORTARS & GROUTS:
Most of these products are received by the installer as bagged dry powder at the job-site. These products are mixed either with a latex admix (polymer in the liquid) or with water alone (polymer in the bag).
To use polymers additives with Portland cement based mortars and grouts products correctly, one should follow the directions of the manufacturer and understand the basic chemistry involved.
In addition to Portland cement, these mortars and grouts typically use graded silica sand and many other additives to help develop useful, user-friendly products. While other raw materials can affect cure time and rheology of the mortar, understanding polymer, Portland cement and water retentive additives is important in making the correct choices in the field.
Portland cements are hydraulic; such as when mixed with water they cure (hydrate) with water to form a stone-like compound. Hydration starts as soon as it comes in contact with water and significant strength gains occur in the first 28 days, if the Portland cement has sufficient water to fully cure. (Actually, Portland cement will continue to cure and slowly build strength over 20 years in the presence of water.) While many other factors need to be considered in designing a mortar or grout, insuring that the Portland cement has an adequate amount of water to cure is important.
Also, keeping the water to Portland cement ratio low is critical to any mortar to develop its best properties. At the ideal amount of water, mortars are not workable and the ideal ratio assumes no water loss to the environment. In the real world, it takes a greater amount of water to make a workable mix and the water escapes to the environment in many ways.
When simple Portland cement and sand systems are applied in thin layers, under a wide variety of humidity and temperature conditions, the cure is often not adequately completed before the needed water escapes. Even if excess water is used initially, all this water escapes rapidly. Hot dry concrete, high temperatures, low humidity, tiles with high absorption and similar job-site conditions tend to pull the water out of the mortars before proper curing can take place. For proper cure (for ultimate performance), it is imperative that sufficient water be present in thin-bed mortars and grouts during the early stages of hydration.
The use of polymer in Portland cement mortars and grouts enhances water retention for better cure, especially in low relative humidity environments. Polymer provides equal work-ability while allowing for lower a water to cement ratio (reducing permeability). Polymer particles coat the cement grains and aggregate forming a continuous polymer film throughout the structure. This continuous polymer film helps maintain the high relative humidity environment within the cement matrix needed for good hydration.
The point is not to have excess water, but to keep the needed water in the mortar long enough to guarantee cure. One should mix with the least amount of water as possible while still having good workability to place the mortar or grout properly. Polymers help to this goal, but sometime you need more.
WATER RETENTIVE ADDITIVE:
Many years ago, water-retentive additives were developed to “hold” water in Portland cement based mortars and grouts. ANSI 118.1 ceramic tile adhesives normally contain a water retentive. Most thin-set ceramic tile adhesives contain a water retentive.
When water is added at the job-site to mortar or grouts containing a water-retentive, the mix must be allowed to slake.
In the ceramic tile industry today, polymer additives are either designed into the mortars and grouts (just add water) or still allow you to add a latex admix to conventional Portland cement mortar & grouts and Dry-Set mortar and grout. All products are designed to perform as recommended; unsanctioned blending of products may have negative affects and “more” is not always better.
In using 1-part polymer modified bagged mortars and grouts, follow the manufacturer’s recommended water demand to obtain good results. Use clean potable water. No other additives should be used since the polymer addition is in the product, unless specifically specified by the manufacturer.
In using 2-part polymer modified bagged mortars and grouts latex with admix, follow the man-ufacturer’s recommendations and only use the products designed as a system. Mixing latex from product A with bagged mortar from product B may result in poor results. Never dilute with water if there are no instruction to do so. If dilution with water is required, use clean potable water.
Again, one should follow the directions of the manufacturer for each product.
When polymers are used with Portland cement mortars and grouts, clean-up procedures are different and sometimes more difficult. Remember polymers build strength as they film form; clean the tools before the films form and it should be easy. Wait and it might be hard.
A chief problem is removing the film from the face of the tiles, especially tiles with a porous surface. Mixing the grout into a stiff mix, applying it with a hard rubber float to leave a minimal amount of grout on the surface of the tiles, and dragging the surface of the tiles with a damp terry cloth towel will usually result in an excellent job. The final pass over the tiles shall be made with clean or fresh water. The most practical way is to thoroughly complete the cleaning procedure shortly after the Polymer grout has achieved an initial set. Removing cured films or minute deposits in the pores on the face of some tiles can be very difficult and time consuming. Follow manufacturer’s instructions for application and clean-up including any special procedure necessary for removing dried or cured films from the face or pores on the surface of the tiles.
The proper use of polymers will aid the ceramic tile industry by reducing call backs, improving the performance of completed jobs, and thus selling more tile. Satisfied customers bring referrals! Learn to use these materials properly.
As formulas vary between manufacturers of the polymer modified materials, the end user must follow the instructions specified by the manufacturer of the product involved.