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Old 01-05-2011, 08:56 PM   #1
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Prep for tile on slab


I'm installing ceramic tile flooring on concrete slab. The floor was poured in 1957, so I don't know if there is a sealer on it or not. We removed some old asphalt tiles and adhesive (yuk) and the clean concrete still has a little sheen on it. What further prep should I do? Do I need to etch with muriatic acid? Sand it? Peen it? Or, am I good to go. I plan to put the orange waffle textured vapor barrier between slab and tiles.

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Old 01-07-2011, 08:31 AM   #2
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Prep for tile on slab


A slab that old with adhesive bonding to it probably doesn't have a sealer on it, but a way to check is to put some water in a spray bottle and spray water on the slab in a few different areas.

If the water soaks into the concrete in a minute or two, there is no sealer. If the water sits on top for an extended amount of time, you probably have a sealer.

If you need to remove the sealer to bond the tiles to the concrete, then lightly grinding the surface is the best approach.

Acid etching may not completely remove all the sealer, could require several applications, then neutralizing and several rinses to remove all acid residue.

http://www.everything-about-concrete.com

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Old 01-07-2011, 07:15 PM   #3
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Prep for tile on slab


Chances are that slab was never sealed or had a curing compound on it, which is good. Although the floor is concrete, you are dealing with the old adhesive residue. I'll assume it's the old black tar based cutback or asphalt emulsion adhesive.

How did you removed the adhesive? How much residue is left? Is the concrete visible or just black? Did you try the water test anywhere yet? Results?

No Muriatic acid indoors, or we might hear about you on the news.

That orange waffle stuff is Ditra......smart move.

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Old 01-08-2011, 09:01 AM   #4
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Prep for tile on slab


Appreciate the input, Jaz and Crete. We removed the residue with a chemical adhesive remover, followed by several soap and water baths. Our house is so dry this winter that it's hard to tell if water's soaking in or evaporating up, but puddles from our boots sit for a good while. I'll run a sander over it with 60 grit paper to give it a little tooth, and I think that should do the trick.

Cheers!
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Old 01-08-2011, 03:56 PM   #5
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Prep for tile on slab


Using chemicals to remove the adhesive was not a good move. Although you were able to remove some of the adhesive, you also diluted and caused more of it to be soaked into the concrete along with the "bond breaker" solvent you used.

Sanding it will work for 2 seconds until the paper gets all gumed-up. I would try a bond test on several areas to see what happens.

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Old 01-08-2011, 08:58 PM   #6
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Prep for tile on slab


What would have been better? Heat gun?

Are there specific problems I should watch for?
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Old 01-08-2011, 09:01 PM   #7
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Prep for tile on slab


OH, and how do I do a "bond test?" Apply some mortar and see if it sticks?
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Old 01-09-2011, 08:16 AM   #8
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Prep for tile on slab


Jazz will set you straight if my suggestions are not ideal----Buy a bag of Kerabond and a Jug of Keralastic---Mix a small batch using a whip and a drill---install a sample tile in the worst area(s)--


After three or four days,knock off the tile and see how it bonded--

I suggest a two part thinset whenever the surface is troublesome.--Mike--
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Old 01-14-2011, 07:34 PM   #9
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Prep for tile on slab


So, I'm making an attempt to grind the adhesive off with pretty good success. Yes, Jaz, the paper's gumming up somewhat quickly, but we got most of the goo with solvents, and I'm getting to a concrete surface fairly quickly using my belt sander. Luckily, this area's only about 8'x8', so it should only take a couple hours and a few dozen belts.

After I finished a good size area, I did the water spray test, and it is absorbing very quickly into the slab, maybe a minute or so. It is visibly faster on the sanded area than unsanded, so I think I've got it resolved. From what I've read here the ability to absorb water is the key to a good bond with the thinset. Yes? Any other thoughts or concerns are welcome.

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