Flooring and Carpeting loose tile over radiant heat, resistant cement, cement type

Flooring and Carpeting /loose tile over radiant heat


Expert: John Michaels — 9/29/2008


QUESTION: I have a house that has radiant heat in the bathroom, covered with concrete, then floor tile was installed over that with thinset. Installed 3 years ago. All the floor tiles are loose, and we are removing them. None of the thinset adhered to the tile. What product should be used to reinstall. Never seen anything like this.

ANSWER: Hi Robert;If none of the thinset adhered to the tile, then it sounds like the installer allowed too much open time for the thinset to set up, so the thinset mostly dried out (skinned over), before the tiles were installed. The radiant heating accentuated that installation issue, if, in fact that installation issue did occur. From your description, it certainly appears it is installation related. How soon after the installation did the tiles first become loose? You may be able to have the residue from the thinset scraped off the adhesive and new thinset properly applied, however it may be necessary to install a moisture resistant cement type backerboard on which to apply new thinset and properly install the tiles. If you had a problem in the concrete, the thinset would have lifted off the concrete and/or any leveler that was used, and stuck to the back of the tiles. The fact that you have just the opposite, may indicate an installation issue. Another thing to check is, with a ruler with increments of 1/16 in. how wide are the trowel ridges, are those ridges very well defined and highly peaked or mushed down, is the concrete level with no low or high spots that would allow thinset to only bond to small sections of each loose tile, and any other observations you may have. If you have recourse with the dealer and/or the installer, you might want to have a certified floor covering inspector visit the jobsite and supply a certified report of his or her findings. If you wish to get back to me with answers to the issues above, or if you have any other questions, please feel free to contact me.

QUESTION: Thanks for the quick response. The ridges of the thinset used are quite defined and peaked. Can the tile be reinstalled with new thinset if we fill in the ridged areas? I was also told that the installer may have turned on the radiant heat to speed up the curing time, which may have cause the problem in the first place.


Hi, again, Robert; You need to remove all the old thinset. One major problem may be that ALL floor covering manufacturers are in the throes of producing ‘green’ products, friendly to our environment. Those products also include sundries (adhesives, grouts, underlayments, etc.) are quite different then those manufacturer even 1 or 2 years, ago. The adhesives used in your original installation may have been petrochemically based, while the adhesives made today, are water based. They may not have an affinity to bond to the existing adhesive, so it has to be removed. Another problem you have is that concrete is absorbent and always moves. The concrete may have absorbed some of that old adhesive below its surface where you can’t see it. So if ALL of the old adhesive is not removed, the residues from it may leach to the surface of the concrete, causing your reinstallation to fail. I would strongly suggest installing a moisture resistant cement type backerboard over the concrete, after scraping away the visible old adhesive residue, and reinstall the tiles on the surface of the backerboard. Visit the website of hardibacker.com, and view the backerboards they have available. Speak with their technical services department for guidance in properly preparing the concrete for the backerboard installation. By installing the backerboard, you will be raising the height of the entire installation, which may require adjustments to door heights, etc.

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