Cracked tile due to an uneven substrate

These tiles were hollow sounding due to using an under-sized trowel.
There are a variety of thin-setting materials, thin-set mortar being only one. Thin-sets are a method for installing, not a product. For example organic adhesives are in the thin-set family, as are epoxy materials. They all have their individual characteristics, and these individual characteristics may lead to problems in the field.

Organic adhesives are divided into three categories. The Type I products are generally approved for both walls and floors. Based on industry standards, determined by ANSI, the American National Standards Speciation for the Installation of Ceramic Tile, the strength values for Type I are substantially higher than for Type II. For example, the Type I after water immersion must have a 50 PSI or greater value whereas after water immersion the Type II requirement is 20 PSI. Naturally there are no values attributed to non-spec material.


The most common failure is the misuse of the product by using:

Tile installed over building paper

1. The wrong trowel size; I have seen floor trowels used on wall installations with the result being tile slippage creating an ugly installation.

2. Applying over unsuitable or questionable substrates such as lauan, fire treated plywood, masonite, wafer board, and other unsuitable or excluded substrates.

3. Curing compounds that prevent achieving a mechanical bond.

4. Installing over damp to wet cement backer boards. This will undoubtedly result in problems, especially where cement backer board is used in areas continually exposed to moisture. Tile grout yellowing may also occur.

5. Installing ceramic tile in tub surrounds with Type II when Type I is recommended by the Tile Council of America.

6. There have also been failures where organic mastic has been used behind ovens with the temperature exceeding 140 F. This results in the organic adhesive getting hard and brittle, with ceramic tile dropping.

7. There have been occasions where there has been skin-over and failures due to excessive field spreading in an effort to save time. This prevents adequate transfer of adhesive to the tile backing, subsequently tiles dropping. Though organic adhesives have their limitations they have a place in our industry. The fact they are not labor intensive ensured that many home builders will install ceramic tile rather than plastic showers.

8. Alkalinity has a destructive force against organic mastic. Alkali is present when moisture or moisture vapor is present migrating from the slab. Do a simple electronic moisture test or pH paper test prior to installing ceramic tile to an on-grade concrete slab. Another method is phenolthaclin.

Phenolthalein liquid being used to show a moisture condition which causes a problem.


There are so many causes for failure it almost makes one wish he had taken up another line of work; perhaps a ceramic tile and stone flooring inspector. That's not too hard on the knees.

Let's start with a New Year's resolution to use common sense and patience with all your jobs. Believe me you will leave problems for others to get a headache. Plus you cut into my inspection income.

Let's first list many problems that occur:

Loss of bond due to:

• Skin-over

• Cracked tile or stone

• Poor substrate

• Steel troweled concrete

• Curing compound on concrete

• Old adhesive/cut back in concrete

• Builders paper as anti-fracture membrane

• Felt

• Cracked slabs

• Gypsum poured underlayments

• Excessive deflection

• Incorrect or no expansion joints

• Adhesive remover

• Dirt, dust, debris


• Using water, hot from the summer sun to mix your mortar. This will cause flash-off and accelerated hydration causing skin-over and preventingproper transfer.

• Not keying in as proposed by ANSI; that is, not spreading with the flat side of the trowel first.

• Not testing for moisture. This can stain light marble.

• Cracked tile or stone. Not having a flat substrate, or lack of coverage, especially at corners. Perhaps not beating in to set the tile.

• Not using a latex modified thin-set for porcelain tile.


• Mix at correct speed, not high speed, to avoid air bubbles and weak mortar.

• Slake your mix.

• Do not over water.

• Do not add water after original mix.

• Don't use hot water.

Some of the potential problems can be addressed prior to installation and these checks can save you time and money. For example marble should not be installed using organic adhesive or gray thin-set mortar, unless you want staining.

Another example is gypsum poured underlayment. Millions of square feet are being poured, with most of it being covered with vinyl. But people now want to upgrade to ceramic tile or wood. If you have an installation to go over gypsum poured underlayment, the safest way to go is with an anti-fracture membrane beneath your tile. Many newly constructed apartments and condos gypsum poured underlayment is poured over wood construction and could possibly face deflection problems.

Some thin-set mortar manufacturers approve the use of their product over the remainder of old cut back adhesive used previously to install vinyl tile. For many installations you may never have a problem. However if you install your ceramic tile over cut back on a concrete slab that is on grade you may face a future problem if moisture appears. Further the cut back will turn to brown soup and your tile will start to float and discolor. My advice is to remove most of the cut back before starting to work; asbestos abatement crews are not necessary. Again, many of these problems can be foreseen so take your time and let common sense prevail.