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We had a basement flood, and consequently had to rip out the vinyl floor tiles in our basement. The tiles were not asbestos (we had them tested).

But after the tiles came up we discovered that they had been secured with black mastic. The adhesive did test positive for asbestos, 4-5%. So now we need to figure out the safest way to proceed with getting new tiles in, in light of that potentially dangerous material.

Contractors we have spoken to think the best approach is to put down new ceramic or porcelain tiles right over the existing adhesive. They said "capping" the mastic in a seal coat or thin layer of concrete wouldn't be a good idea- they'd need to pour rather a lot of concrete for that.

Originally the contractor wanted to grind the floor (which I've read is exactly the wrong thing to do if mastic has asbestos!) When I balked at the grinding, he said he'd instead use a "fortified mortar" to lay the new tile down. I believe he also referred to this as "high polymer" mortar.

My question: can you lay down ceramic/porcelain tile over existing mastic without grinding the floor? Will it adhere suffiiently? Is there a better/safer approach?

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I know this is an old question but you would us a modified thinset and tile. NO NO NO you do not use mastic for a basement floor. Next time it flood you will have tile/asbestos coming up. If this option wasn't discussed with you then you had the wrong contractors.

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An electric tile chipper with a 8-12" sharp blade can be rented cheaply to do the job. Dust level is low but Work with masks and forced window exhaust. It's like a cross between a jack hammer and a sideburn shaver and easy to use . 1 hr to separate from concrete . 1hr to haul out. 1hr to rental place and back. for 500 sq ft.

If it is smooth enough, extra tile adhesive will work too to even out the bumps.

  • I'm concerned about the asbestos-laden dust this will create in my home. – user25271 Sep 16 '14 at 13:56
  • When I did it with my Mother's basement circa 1958 asbestos tiles, there was no visible airborne dust , But a 500W halogen lamp would be good tell,if there is in your case and use a large fan in basement window. You just want to chisel off the excess and the tool has a 12" vibrating chisel. Shop vac should have filter paper, just in case or use a broom. Its much heavier and coarser than drywall dust to be airborne – user25261 Sep 16 '14 at 14:28
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    In most places it is illegal to hire a contractor remove known asbestos containing material if that contractor doesn't have a license for asbestos removal. Most places it is legal to do it yourself but illegal to dispose of it at a dump/trash. You still have to find a site to take the asbestos containing material, and most don't work with the public. – diceless Sep 16 '14 at 15:15
  • Also I think you might have misunderstood that we have already had the tile removed- it's only the mastic that remains. We didn't even know it was there until after the tile was removed. – user25271 Sep 16 '14 at 21:54
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I'm not experienced enough with tile to answer the question directly but have you considered other floor coverings? They make engineered wood that is rated for below grade that will float above the old mastic. As long as the mastic is generally smooth (no ridges between the old tiles) it will go down just fine.

Cost is about the same but if you have a table saw and a miter saw you can do the install yourself. Laying a floating wood floor doesn't take the same skill level as tile does.

  • Although we have taken great pains to keep our basement dry (sealing the outer wall), we don't think wood on the floor is a good idea. The latest flood was from a sewer backup. Fun. – user25271 Sep 16 '14 at 21:56
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Call up one of the suppliers of polymer-modified thinset, and see what they say. They are the ones who can tell you whether it works or not.

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