How to remove or encapsulate floor adhesive in attic subfloor?

April 2, 2015 4:18 AM

We are doing a total gut renovation of our house, and the glue holding down the old attic tile is this black stuff that smells like tar. What do we do about it? Paint over with Killz? Steam and scrape off? Something else?

I don't want the smell in the attic, and while we will use the attic primarily for storage, it is a bedroom technically and I will be putting down some kind of inexpensive flooring down over the subfloor.

Have you done this before? Any experience with using Killz or another heavy duty primer? Did you scrape it off, or steam it off, or simply cover up?

posted by teragram to Home & Garden (11 answers total)

Response by poster: If helpful: a photo of the subfloor.
posted by teragram at 4:33 AM on April 2, 2015

Best answer: Most flooring systems are strong vapor barriers, and as such, strong odor barriers. When I recently pulled up some engineered flooring in my bedroom, it became abundantly clear that it was laid down primarily to cover the strong, strong odor of cat urine that was soaked into the original floor. (Which, in turn, I pulled up because - ugh). If odors are your only concern, lay down 35lb roofing paper, then your flooring, and you'll be fine.
posted by klarck at 4:54 AM on April 2, 2015 [1 favorite]

We opted to scrape ours, it was tedious but worth it.
posted by julie_of_the_jungle at 4:54 AM on April 2, 2015

Some kinds of flooring glue contained asbestos. Get it tested before scraping or otherwise disturbing it; otherwise just put new flooring over it and ignore it.
posted by Dip Flash at 5:01 AM on April 2, 2015

I have scraped floor adhesive like that. It is tar btw. You can sand it off but you'll go through a lot of sandpaper (rent a floor sander). Another option would be to cover it with floor leveler - labeled "universal skimcoat & patch" and then prime with floor multipurpose primer and sealer. That's what I just picked up to cover old adhesive on top of tile. The reason for the primer is to help adhesive back (cheap!) tile stick because they're not super sticky. If you're laying down something else you might need a different prep.
posted by leslies at 5:02 AM on April 2, 2015

I removed mine off my basement floor (cement) with combination of scraping and use of Sentinel 747. Even with the adhesive remover (which you let sit on the floor to soak in and loosen the tar) it was still a pain in the butt and took hours upon hours and lots of elbow grease. I still couldn't get all of it off. If I had to do it over again I might just leave it there and cover it up.
posted by canda at 5:05 AM on April 2, 2015

Yeah, definitely sample for asbestos before you do anything. Most mastics (glues) contained asbestos (as a bulking agent -- so they could be tar + asbestos, basically) until maybe 20-25 years ago. (In fact, some still do; asbestos isn't actually illegal in the US. Check your roofing patch for chrysotile asbestos, everyone!)

If it does contain asbestos, you can probably cover it over (aka encapsulate). I wouldn't scrape unless you've tested.
posted by pie ninja at 5:21 AM on April 2, 2015 [1 favorite]

We had the exact same stuff in our original hardwood floors that was covered by the black stuff and then a layer of tile.

Echoing what everyone else said, 1) Get the tile (if you haven't already disturbed it significantly) and the mastic tested for asbestos. We sent samples to Western Analytical Laboratory and they returned data results very quickly. Luckily in our case we didn't have asbestos.

We wanted to keep the floors and refinish them, so it came down to a lot of hand scraping. Machine sanders will get gummed up, so don't even try it. I found a hardwood floor hand scraper, a file to keep the scraper sharp, and lots of hot water with a little tsp (goo gone, "mastic remover" and everything else worked poorly when compared to the hot water/tsp solution) worked best.

In your case if you just want to lay flooring over it, I wouldn't worry about it too much (unless it has asbestos) and just leave it. - you can easily get a floating floor or a some other floor that sits on a layer of foam that would cover it up.
posted by Karaage at 6:07 AM on April 2, 2015 [2 favorites]

After testing for asbestos and pulling up any excess tarry paper my friend & I were able to make short work of it with a drum sander (in a small 10x10' kitchen). It probably gummed up one or two extra high-grit sander rolls. The orbital sander we rented first didn't make a dent; it was definitely a drum & high powered edger job.
posted by deludingmyself at 8:08 AM on April 2, 2015

Best answer: Seconding the asbestos testing, but if you're going to use the space for storage and (someday) a finished bedroom and the tests are clear, just lay down red rosin paper and then nail down 1/8" plywood over it. Don't bother cleaning up a subfloor you're never going to see again.
posted by JoeZydeco at 8:08 AM on April 2, 2015 [2 favorites]

Response by poster: Thanks, all. We ended up putting down a layer of flooring vapor barrier, followed by a layer of OSB Avantech and ta DA! Tar smell is gone (or at least very barely perceptible).
posted by teragram at 5:58 AM on May 5, 2015