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I want to put ceramic tile a concrete basement floor that previously had vinyl tile installed with a black, asphalt-looking mastic. I have had mixed advice on whether I need to remove the mastic. One person said to use a more expensive, general purpose thinset – that my problem was a common one and the gen. purpose thinset worked fine. Better advice, I think, was to remove the old mastic, but it is very difficult to scrape off or sand off. A 4″ grinder worked fairly well for about a square foot, but I’ve got 600 sq. ft. to do and it looks like it would take a week to get the stuff up. Any recommendations on the need to take off the old mastic and/or how to remove the mastic would be appreciated. Are there rental tools available that will work on the mastic? I don’t think a sander will work as it just gums up by belt sander almost immediately.
Thanks,
Mike
Replies
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Mike,
If the old mastic is clean free of dirt and sound ( stuck well ) you can probably go straight over the top with thinset, though you may have to use a slightly larger comb than usual.
Mark
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I scraped a 500 square feet of that stuff before, and it's not any fun. Armstrong (vinyl manufacturer here on the e-coast) makes a stripper for it, but I think it may be specific for their mastic, and you've got to use it in heaps, but it works really well with just spreading it out and taking a scraper on a pole to it (scraper need to be fairly sharp in scraper terms). Respirator definitely recommended. I did this manuever because I was going back with vinyl and being very thin, the old mastic would've created problems. Seems like if you had some portion of the slab available to adhesion with the mortar, then it might be fine and the mastic might even form a sort of vapor barrier. Anyway, it took us less than an hour to scrape 100 square, and in terms of the doing it, that is why the industry has provided us with mexican laborers.
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The portland cement based thinset mortar will not bond to the vinyl mastic residue called "cutback". If in doubt of what I say, contact the thinset mfg.
You have two options. One, rent a floor scraper designed specifically to remove the cutback. It's a terrible beast, you'll feel like crap after the day, but it will be done and done right. Just keep the blade sharp. A pack of blades and a file will do it.
Your second option is to encapsulate the cutback. Pour a minimum thickness layer of self-leveling mortar over the floor.
I like the second option. When I have done this, I roll concrete glue over the floor with a 1/2" nap roller and let it tack up for an hour. Then, working fast, pour the self-leveling.
With either option, you can knock out 600 feet in less than a day. If you decide to go with the second option, let us know so we can give you more of this expensive, but free advice.
*Hello Rich,Maybe what we call thinset isn't what you call thinset. Our thinsets are not mortar based, and I agree with your call on not using a mortar based glue in this situation.Wherever possible we use a two pack latex adhesive like " Resaflex" ( do you have that over there?) which is highly flexable and waterproof.regardsmark
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I want to put ceramic tile a concrete basement floor that previously had vinyl tile installed with a black, asphalt-looking mastic. I have had mixed advice on whether I need to remove the mastic. One person said to use a more expensive, general purpose thinset - that my problem was a common one and the gen. purpose thinset worked fine. Better advice, I think, was to remove the old mastic, but it is very difficult to scrape off or sand off. A 4" grinder worked fairly well for about a square foot, but I've got 600 sq. ft. to do and it looks like it would take a week to get the stuff up. Any recommendations on the need to take off the old mastic and/or how to remove the mastic would be appreciated. Are there rental tools available that will work on the mastic? I don't think a sander will work as it just gums up by belt sander almost immediately.
Thanks,
Mike