Frequently Asked Questions (FAQ)

The size of the tile determines the choice of trowel. Large format tiles (where any side is larger than 15" [38.1 cm]) require a square-notch trowel with deeper notches like 1/2" x 1/2" x 1/2" (12 x 12 x 12 mm). Smaller sizes can be installed with a 1/4" x 1/4" x 1/4" (6 x 6 x 6 mm), or 1/4" x 3/8" x 1/4" (6 x 10 x 6 mm), square-notch trowel.

There are several recommended surfaces such as: plywood, concrete, gypsum and cement backer units (CBUs). All require different preparation. For more information, see the technical document “Surface Preparation Requirements.”

Polymer-modified mortars are recommended for tiling over plywood.

Oriented strand board (OSB) is a problem for resilient and wood flooring installations because of the nature of its construction. Traditional OSB is made from large chips of wood that will swell when exposed to humidity and moisture, causing the texture of the chip structure to show through on resilient floors. According to the Engineered Wood Association, OSB is only suitable as a substrate for stretch-in carpet, which isolates the texture of the OSB from the flooring with a layer of carpet pad. The association goes on to recommend applying a 1/4" (6 mm) layer of underlayment over the OSB for installation of resilient and wood flooring. The main thing to remember about traditional OSB is that it is very absorptive and swells when exposed to moisture (such as rain). This swelling is not good for floor installation. Having said that, there are new OSB products out there that are “engineered” materials, making them different from traditional chip/strand OSB. Some of these new engineered OSB boards have much better moisture resistance and can handle water contact without a change in dimensional properties.

Yes, although Flexcolor CQ grout is a pre-mixed grout, it may need to be stirred before use.

PH-neutral UltraCare cleaners are available for this purpose.

It used to be said that solvent-based products were more durable and longer lasting than water-based products. In today’s world, we have water-based technology that is equal to, or better than, solvent-based products. Because of its unique molecular construction, UltraCare Penetrating SB Stone, Tile & Grout Sealer is formulated for use on both porous and dense surfaces.

MAPEI recommends a polymer-modified thin-set mortar such as Keraflex RS under and over the membrane. Be sure to carefully follow the water ratios and all other instructions listed on the products’ Technical Data Sheets.

The thin-set mortars recommended for waterproofing membranes are polymer-modified thin-set mortars. Do not use mastics such as Type 1 or Ultramastic ECO on waterproofing membranes.

The reason for so many trowel types is that there are so many flooring types. Think about what is being installed: Everything from thin vinyl sheet to 3/4" (19 mm) solid hardwood flooring. Each flooring material has unique properties. For example, a thin vinyl sheet is very flexible, so you don’t want heavy trowel notches on the floor as they will show through to the surface of the vinyl (an effect called “telegraphing”). So for thin resilient flooring, we typically recommend very finely notched trowels. Wood flooring, on the other hand, has a variable backing structure. Some may be smooth – others, grooved or cross-cut – so you need a trowel notch that can lift and shape the adhesive in such a way that it comes into solid contact with the flooring material. Further, wood flooring is very rigid and does not bend or conform to the subfloor. Therefore you need to use a trowel notch that accommodates for subfloor flatness and still brings the adhesive into contact with the back of the flooring. Using a thin-notched trowel for this would not allow for proper adhesive transfer. The same thing is true of broadloom carpet. Typically, broadloom carpet has a rough-textured backing. In order to get proper performance out of a carpet installation, you need to make sure that the adhesive gets into this texture and that is why this application includes recommended trowel notches that create high ridges. In summary, smooth-backed flooring materials are typically installed using finely-notched trowels while texture-backed materials get installed with larger-notched trowels.

There can be different explanations of why this happened. The grout may have been washed too soon or too much during the cleaning process, causing pigment to be removed from the grout. Or, the grout powder may not have been dry-blended before mixing in order to avoid color variation.

This indicates that too much water may have been used either in the mix or the cleaning process.