Removing mastic from concrete subfloor

Old 04-10-05, 09:28 PM
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Question Removing mastic from concrete subfloor

I'm trying to remove some mastic from a concrete subfloor that held parquet flooring from 1951. The mastic has been analyzed to only have 3% chrysotile, so I'm taking the precaution of using the HEPA mask. However, using a floor scraper with amended water has not been effective. Also tried using an adhesive remover, which seemed to make more of a mess than actually remove the mastic. Is there anything else I can try? Is there a sanding tool that I should be looking for instead?
Old 04-11-05, 05:19 AM
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You can try boiling water to soften it. I would not sand it. There should never be any mechanical removal of anything containing asbestos and chrysotile is in the asbestos family. Solvents will inhibit the bonding of thinsets to a slab. Using just the hot water and a shop vac to suck up the slury, just test a small area, say 2x2, scrape as clean as you can without going to crazy nuts and then do a bonding test using a thinset rated fro use over cutback adhesive. Set 2 or three tiles in the area and wait about 2 or 3 days, then try to pry up the tiles. If you've purchased expensive tile for the project, just go to HD or Lowes and pick up a couple of there cheapo less than one dollar tiles for your shear test. If water isn't breaking it down, then you will probaly have success with a highly modifed thinset, either one of the $25-30/bag types or an unmodifed thisnet ($8/bag) mixed with the brand's liquid latex additive instead of water. Don't use solvents, not only do they make a mess (as you've found), they can be bond breakers for thinsets, can create highly explosive atmospheres in insufficiently vented areas (picture the fumes getting to yur pilot light on your hit water heater--KABOOM) as well as being harmful to that gray matter betwen your ears. Let us know how the bond test works.
Old 04-12-05, 06:44 AM
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The boiling water seems to be working on getting the glue softened enough to scrape it up with a spatula. It's slow going, but no one said it would be easy. At least I am finally getting somewhere. Thanks! I don't think I will need to try to bond test, as I plan to put a engineered wood flooring over it once the glue is mostly gone & I can even out the subfloor. Not sure if the glue would affect a leveling compound on the concrete or not, but I figured it was best to just remove the glue since it was making the floor very uneven. I posted here because there seemed to be more about removing adhesives going on in this forum than the wood flooring forum.
Thanks for the information!

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