Many times, a jobsite is not well maintained or kept clean which can be an image and possibly a safety issue, but more importantly, when tile is being installed, the substrate must be clean. During our discussion, we will be focusing on the requirements for concrete floors. 

The following excerpts of American National Standards Institute (ANSI) standards clearly state these requirements: 

A108.01 – 2.6.2.2 Surfaces must be clean, free of wax, curing compound, and other coatings.  

A108.5 – 2.2 Clean surface thoroughly. Dampen if very dry, but do not saturate.

Likewise, the Tile Council of North America (TCNA) Handbook Requirements for concrete slabs states, “Slab to be well cured, dimensionally stable, and free of cracks, waxy or oily films, and curing compounds.” 

These standards and methods clearly state that the surface must be clean, but many jobsites provide numerous items that will inhibit a good bond for commonly used dry-set cement mortar. Construction dirt can, most times, be effectively removed with a HEPA-filtered vacuum and damp mopping the surface. This sequence, vac first and wash second, is crucial for success. 

However, if the concrete is contaminated with a curing compound, topically applied sealer, oil-based sweeping compounds, oil, kerosene, or previously-applied adhesives, they must be appropriately removed. This is where it gets tricky. Many of these contaminating products can be successfully removed with a solvent or other cleaning product, but in loosening the contaminant, they are being emulsified into a liquid for easy removal. The problem occurs immediately due to the liquid being absorbed into the porous surface of the concrete which is many times not easily or may be impossible to remove. 

OSHA-approved surface grinding equipment may appear to solve the problem, but many times it doesn’t go far enough to reach the emulsified product and sometimes the grinding may actually drive the problem even deeper into the concrete. Most likely the best way to eliminate the problem is to shot-blast or bead-blast the concrete substrate which removes about 1/8” of the top surface resulting in a bondable substrate. Once the correcting process has been completed, simply pour a small amount of water on the surface. If is soaks into the concrete, you are good to go, but if the water beads up and just sits there, the contaminant is still present and more work is required. 

The last contaminant to be discussed is not on the above list and most people don’t consider it to be a problem. It is drywall dust and joint compound globs. These items may seem innocent enough, but if they are not vacuumed up first, the resulting slurry can make the surface unacceptable to the mortar. Always scrape up the bulky material, thoroughly remove the dust with a HEPA-filtered vacuum followed with a damp mop.

The bottom line: don’t rely on liquid solvents (be aware of potential fumes and flammability), or citrus-based cleaners to remove the existing residue. They may eliminate the first problem, but they create another one.