There is a lot of chemistry behind most tile installation products, especially in the case of setting bed mortars, thinset mortars and grouts. A wide variety of tile installation mortars have been produced using acrylic- and liquid-latex additives -- instead of water -- mixed with dry sand and cement. My first experience with latex involved making a large amount of strong thinset mortar. A 100-pound bag of fine (60-mesh) was blended with a 94-pound bag of Portland cement in a mixing box and mixed with a slotted hoe. This was combined with a latex additive in 5-gallon buckets. Even though power mixers were used to make the thinset, the entire process required a lot of work and hauling.

These basic latex products are still quite popular and are readily available, but a new generation of polymer thinsets and grouts is simplifying the installation of latex grout. It is important for installers to understand the differences between regular and enhanced mortars.

Regular thinset mortars and grouts are mixtures of dry sand and cement. Water is added to make a smooth adhesive paste. The chemical process that turns the powders and water into hardened mortar requires that a certain amount of water be present in the material being cured. No water means no curing, thus the requirement for keeping the material moist by damp curing.

These same dry ingredients, when combined with a liquid latex (natural) or acrylic (manufactured) additive, make latex thinset. Latex has proven its worth as a tile installation component, but not all latex materials are the same. Some may not be suitable for exterior applications, and others may not hold up under continuous exposure to water, such as in a pool or fountain. Too much latex may lead to leaching, and the concentrated maintenance effort to remove the white latex deposits that result; too little reduces performance. Latex is a requirement for installing porcelain tiles, yet not all latex is capable of bonding sufficiently to porcelain.

The tile industry has yet to adopt a standardized label that is useful to designers, salespeople and installers for rating the desirable properties of latex. These groups need to be able to rate the materials available so that specifications and expectations can be realized. For now, keep a file of product brochures and compare the performance in several areas, including:

  • open time
  • positioning time
  • length of cure
  • minimum cure
  • bond strength
  • compressive strength
  • resistance to chemicals
  • dry/wet ratios.

    Some liquid latex products are designed to be diluted, while others are meant to be used at full-strength. Knowing the differences and capabilities will result in the most appropriate and economical material being specified, sold, and installed for a particular project.

    There are many comparisons to be made between different brands of latex thinset mortar. Polymer-latex thinset mortars and grouts differ primarily in that the acrylic is added as a dry powder to the other dry ingredients at the factory. Delivered to the jobsite in dry form, polymer-modified thinsets and grouts can be shipped for considerably less expense than the liquid additives that are composed primarily of water. Polymer-modified mortars only need water to be activated. With liquid additives, it is difficult to tell visually if an additive is full-strength or if it has been diluted and watered down—an attribute that, unfortunately, is exploited by some unscrupulous installers.

    Polymer-modified also includes liquid additives that are mixed with a basic powder to produce different kinds of thinset mortar. For example, one manufacturer’s thinset powder base can be mixed with one liquid to produce rapid setting, another to lengthen the open time, or a third to promote crack suppression. On a recent installation built over a radiant heat grid, a specific brand of polymer-modified thinset was selected specifically for its ability to absorb the structural and thermal movements found with the system.

    The wide range of choices present a lot to sort through, but polymer-modified thinsets and grouts offer plenty to the installer who wants to build a business on quality and performance.