Mortar over cutback residue? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-26-2014, 09:42 PM
Hello all, please advise! Working on putting new ceramic tile in basement. Originally (house built in 1951) owners put down asbestos containing (I think) tile, with the black adhesive (cutback?) under it. At some point some of that tile got removed and replaced with ~7.5" square ceramic tile over the existing adhesive. I removed this ceramic recently, with great ease, using a hand chisel. It appears they did use a thinset mortar, and the thinset came up with the tile. Only a few very very small patches left on floor. The tile was in great shape, no cracks in it or the grout. The concrete is in excellent shape as well, only a couple small (maybe 1/32" wide) cracks. This tells me that the previous thinset did ok at holding the tiles down, right? After I pulled the tile up there was a bad musty/mildewy smell. That lasted for around 4 days then pretty much was gone. I did a moisture test (with the plastic sheet) on the concrete and got a few very small droplets after 5 days. Done a fair amount of research now on membranes (liquid, ditra) and application, and am kind of torn between putting the tile down right on concrete or doing ditra. I'll be laying ~80 sq. ft.. I can surely get some pics if that would help on advising. Thanks in advance!

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01-26-2014, 09:49 PM
Welcome, John. :)

If you'll type cutback into the Advanced Search feature and ask for Titles you'll find a great deal of discussion about tiling over that substance.

In general, when ceramic tile bonding material manufacturers indicate their product for use over cutback, there is a caveat that the cutback must first be scraped off, essentially to the thickness of a stain.

If your current floor has a thicker build up than that, I recommend you go to work with a razor scraper and hot water regardless how you elect to do your new tile installation.

Some photos of what you have would likely be helpful.

My opinion; worth price charged.

01-27-2014, 04:38 PM
Thanks, CX.

I'll probably go ahead and start scraping. I called TEC and they basically said the same thing; if you can get a fingernail underneath it then it should be removed. What are your thoughts on the ditra? Do you think I need it? Good insurance or waste of money?


01-27-2014, 04:53 PM
An uncoupling or crack isolation membrane is always good insurance over SOG as far as I'm concerned.

My opinion; worth price charged.