What are the Standards for Thin-set Adhesive Coverage/Contact for Ceramic Tile?


I have tiles that were installed concrete slab and have hollow sounds when tap on the corners, edges, and i have voids that are more then 2 in. sq. The sound is coming from the top of the tile since thin-set was not applied correctly by the contractor. I have 12x24. on some tiles i have half of the tile hollow the other half is not. I don't find any tile information stating what the industry standard is. I did go to state license board and they told me that tiles do not need to have thin-set on corners and that voids larger then 2 in. sq. is acceptable. They stated as long as the tile has a little thin-set anchoring the tile this meets industry standard. I came across your blog and your stating different. Can you help me?


ANSWER - First of all, per industry standards hollow sounding tiles are not considered a defect per-se.  Although a hollow sounding tile, or a portion of a tile sounding hollow, can possibly be a symptom of a defect.

There are many reasons why a tile can sound hollow and it not be a defect.  The tile could be installed over a membrane of one type or another.  The underlying substrate could be hollow sounding.  Some reasons why a hollow sounding tile can be an indication of a defect is if there are excessive voids under the tile or if the tile is actually loose.

So it is important to have other evidence of a problem in addition to the hollow sounds to substantiate that there is a defect.  So you can't assume that because a tile sounds hollow that there is a problem.  Although if a portion of a tile floor, or a portion of a tile, is hollow and the other portions are not hollow that might indicate there are voids under the tile, but not always.

So you have remove tiles under various conditions to determine what is causing the hollow sound and to determine if there is any evidence of a defect.

The person at the state contractor's licensing board who told you that it was not necessary to have the thin-set adhesive at corners and said as long as the tile had a little thin-set adhesive contact it would meet industry standards is absolutely wrong.

The ANSI A108.5 and A108.19 standards for ceramic tile or porcelain tile, which is a type of ceramic tile, are the standards that state what are the required thin-set coverage/contact (meaning full contact between the back of the tile and its substrate) is as follows:

  • Per ANSI A108.5 the average uniform contact area, for ceramic tiles installed on floors, shall be not less than 80% except on exterior or shower installations where contact area shall be 95%.  The 80% or 95% coverage shall be sufficiently distributed to give full support to the tile with particular attention to provide support under all corners of the tile.

  • Per ANSI A108.19 for gauged porcelain tiles or gauged porcelain tile panels/slabs installed on floors, in any single square foot under the embedded tile, thin-set coverage will be a minimum of 85%.  Coverage shall be sufficiently distributed to give support of the tile, especially at corners and edges. The required thin-set mortar coverage must be sufficient to provide support under the tiles with no voids exceeding 2 inches square (size of golf ball).  Partially collapsed trowel ridges where the dimension of length or width are less than o.25 in. is not considered a void, nor will it affect the longevity or define an installation as unsuccessful.


2 thoughts on “What are the Standards for Thin-set Adhesive Coverage/Contact for Ceramic Tile?

    • Donato Pompo says:

      As stated in the comments above, hollow tiles is not technically a defect in the tile and stone industry because tiles can sound hollow for many reasons. The hollow sound might be due to the underlying configuration of the tile assembly such as membranes can cause hollow sounds or installations over framed walls can cause hollow sounds. Installations over uncoupling membranes can cause hollow sounds.

      Although hollow sounds can be a symptom of a deficiency. If a portion of a tile is hollow that might suggest there are voids under those spots. If some tiles sound solid and others sound hollow that might mean that the hollow sounding tile is loose or isn’t adequately bonded. Symptoms of a loose tiles or excessive deflection in the floor is that the grout will crack.

      The only way to determine if there are deficiencies or what those deficiencies are is to forensically remove some tiles under various conditions to look for evidence of why there are hollow sounds in those locations.

      The tile contractor is not correct on what are the standards for thin-set adhesive contact between the back of the tile and its substrate. The standard for interior floors in dry areas is 80% contact and the 20% voids have to be dispersed. You shouldn’t have a void larger than 2 square inches which is about the size of a golf ball. All corners and edges of the tile should be fully supported with the thin-set they will have a propensity to crack.

      Even though the tiles might not meet the 80% contact they may still be well bonded. The downside is that areas with excessive voids will be susceptible to cracking or crushing if something heavy or sharp falls on those spots.

      In cases where there are excessive voids, some people will try to remediate by injecting epoxy or a latex product called Fix-A-Floor. I have seen this work a couple of times, but more often it doesn’t work because the filler can’t reach the voids. as they try to inject it though drilled holes in the grout joints.

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