flooring over black mastic

Discussion in 'Floor Preparation' started by Oifla, Dec 20, 2015.

  1. Oifla

    Oifla New Member

    hello all,

    i'm working on updating the basement of a 1960-ish house. pulled up the existing (gross) carpet and discovered vinyl tiles. too many were lose to try to keep them in place so i scraped them up and almost all of them came up without any real struggle. under the tiles there's the typical black mastic. the mastic is not sticky nor thick enough to cause a problem (in terms of bumps, etc). i did a couple of tests and i was not able to scrape it off (more like a stain on the concrete at this point, hence the loose tiles) nor make it do much of anything with a heavy duty wire brush on my 4 1/2" grinder.

    i have two questions:

    a) i would like to tile part of the basement. if necessary, i can put down concrete board and tile right onto that. i say if necessary because i'd prefer not to. can i tile right over the mastic?

    b) ideally, the rest of the basement will be carpeted. there too i could install something on top of the mastic and glue the carpet to it or i could ask the installer to use a pad. i would like to avoid those options for several reasons but mainly the potential for humidity. would it be possible to glue carpet down right over the mastic?


  2. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    I would warn that glueing carpet to the oil in that mastic could cause a problem in the future with adhesive failure or bleeding into the carpet. I have installed carpet with pad over that floor and had no problem. As far as tile, I don't know if you could put like ditra mat over that and it would stick for the long term tile has.
  3. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    You can apply a sealer/primer for the carpet from Mapei, Mohawk, and probably a few others.

    For the ceramic, I believe there are thinsets to go over cutback adhesive, I would contact Mapei, they have full line of products and can handle both carpet and tile situations.

    You could also have it tested 25$, send the adhesive to lab to determine if it's asbestos. If it's not, you can grind the resodual cutback off with diamond grinder and vacuum attachment designed for such purpose, then just use normal bonding products over the clean slab.
  4. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    So you cleaned the surface residue with a wire brush on a typical hand grinder?


    Anyways, your tile popped up so easy and took all the glue up off the slab on the back of the tile because the alkalinity of your basement concrete is likely very high. This is caused by moisture passing through the pores of the concrete bringing the salts to the surface which in high concentration can be extremely CAUSTIC.

    The wire brush treatment has already dealt with some of this. Was there a lot of dust? Regardless after vacuuming up any dust at this point I'd wash down that slab with a solution of vinegar and piping hot water. Use about 2-4% white vinegar and RINSE well. The goal is to first clean any loose dust and debris and then neutralize the high pH levels from the many years of those salts collecting under the cutback adhesive.

    For thin set and ceramic tile you should be good to go. For any kinds of adhesives I would skim coat with something like Ardex Feather Finish--------cementitious, latex fortified floor patch.
  5. JPfloor

    JPfloor Pro Member


    Using most any type of carpet adhesive directly over old cutback (black mastic) will create an oily, messy, science experiment you don't want to be part of.:cool:
  6. eaadams

    eaadams Sport Floor Pro

    What are the rules for black mastic and asbestos? I was talking to an inspector the other day and he said the rule in California is is black mastic is now presumed hot until proven otherwise.
  7. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    I got the same rule for Jennifer Aniston.

    I'd use the if it's black adhesive test it before disturbing rule. Recently I became aware of popcorn ceilings possibly containing asbestos. I have a sample I haven't sent out yet.
  8. Jim Decker

    Jim Decker Pro Member

    black mastic

    follow mfg's installation instructions most will not advise installing over mastic of any kind,
    Some say scrape to concrete but the black mastic or any mastic will not be a suitable substrate to glue to. If you must try gluing to a small area and then glue to an area without. Try to remove and see how well it holds before you do any large area.
  9. eaadams

    eaadams Sport Floor Pro

    Thanks Jim, yes understood. My question was more focused on asbestos. I know if I see the smaller 9x9 tiles to assume asbestos, but the asbestos in the glues were around a lot longer than the 9x9's and even past the short period of 12x12 asbestos tiles.

    Dont know if there are any pro tips for when to keep an eye out for black glue and asbestos vs. black cutback without asbestos. (or was cutback always asbestos? sorry I'm a young one)
  10. Asphalt cutback adhesive (S-89 for example) was available up until just a couple of years ago. There are also still several black adhesives on the market such as Henry's 130 VCT adhesive. Obviously, they do not contain asbestos that recently.

    However, you should ALWAYS assume it contains asbestos until you test it. You should always check to see what the local codes or requirements are for removal so you don't have a problem. No ones health is worth guessing. Just my opinion.
  11. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    No, not really any easy way to tell from the tile size that it's safe without testing.

    It's not really any kind of a sure thing with the glue either. There was cutback without asbestos and there were emulsions and thin spreads that were black with and without asbestos (I think, not sure on that). I can tell those from cutback by the smell, notching and texture when heated but I wouldn't ever assume no asbestos.

    It's a foggy memory but I think the Old Timers told me some emulsion adhesives were mixed on site and asbestos was added------or maybe that was the FLOOR PATCH-----or maybe the floor patch/glue/emulsion were all one and the same.

    It was the '70s when they were telling me the stories and I think they were talking about installations going WAY back to the '30s-'50s.......maybe even the '60s
  12. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    It's not much better when they use the adhesive removers either. Did an elementary school multi-purpose room just before Christmas that had asphalt tile and cutback abatement. The did a much better RINSE than I'm accustomed too but it's still a lot of...........science experiment going on when we try to patch and glue over it.

    For informational purposes only--------we use 12 grit sandpaper or the Diamabrush on the concrete to clean away as much residue as possible. In some cases we will prime with Ardex primer. I didn't use it in this case. One or twol coats of Feather Finish over the slab is the BARE MINIMUM prep. I like to put two heavy coats but this slab was pretty smooth and clean so I kind of skimped here. Where the cracks are bleeding the alkaline salts and adhesive remover we sand/grind off and patch an extra coat.

    Don't try this at home kids.

    Attached Files:

  13. Hanover Fist

    Hanover Fist Pro Member

    What everyone is saying here, to summarize, is that black adhesive under what appear to be vinyl tile, might actually be 'cutback' adhesive - a glue that was used up until the mid 60s for adhering asbestos tiles.
    If your tiles are that old, or happen to be the standard size for asbestos tiles*, 9", and you got any of that tile airborn, even the tiniest amount, you may have a health issue on your hands.
    If you have any left - have it tested.

    *the most common asbestos tiles were 9" or 9.5" square - there were other sizes available, but the vast majority were in this size range.
  14. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    Many, many BILLIONS of sqaure feet of 12" vinyl asbestos tiles were laid and I'm sure there are still many billions of sqaure feet still on floors everywhere you could imagine floor tiles being installed from the '60-'70s and briefly into the '80s
  15. Hanover Fist

    Hanover Fist Pro Member

    I stand corrected
    Well, I'm sitting actually.

    But yes - as I'd said, there are other sizes, even 6" tiles - I saw lots of them in Aspen/Vail.
  16. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    I'm looking at these jiffy store, gas station type businesses I go in, they are 12's and places I see that are chipped out have black asbestos under them. FYI Lotto tickets, powerball 300 mil, if I win I'm not looking at another floor for flaws.
  17. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    You better share...
  18. fcfc

    fcfc Pro Member

    don't you always look at floors though and point out the flaws. My wife says that she hates going into any commercial place with me because I cannot help but point out the little things that invariably are wrong with the floor.
  19. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    With that much I will share with TFP members.

    I've never tried to not look at floors in I don't know how long, but I think it's time I specifically try to set a goal to test myself if I can do it. Maybe start in small increments, 1 whole day perhaps. Annoys my wife as well, wouldn't want that!

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