tile over concrete & black mastic [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-07-2003, 01:04 PM
i have pulled up carpet and vinyl tiles to reveal my concrete slab (there's not a moisture problem). my original idea was to acid stain, but there is a thin but stubborn layer of black mastic/cutback on the floor that we've tried to remove with chemcial stripper, adhesive remover, minersal spirits, etc. the mastic is not going anywhere.

my question: do i need to do anything special before putting down the thin set and tile (such as a concrete based underlayment)? thanks in advance

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Sonnie Layne
01-07-2003, 01:39 PM
It's generally recommended to scrape up all the cutback you can. Chemicals don't work so well unless you get into some really nasty and volatile stuff. Get yourself a good floorscraper and a file (to keep it sharpened). It's a workout, but the best way I know of to get the most of it up. Anyway, get all you can, then use the best thinset you can buy.

Others will be here shortly, maybe with better advice. Good luck, and welcome to the forum.

01-07-2003, 02:37 PM
Nicole, glad you made it over to the site. If you search for "cutback" you should find lots of responses dealing with your situation.


John Bridge
01-07-2003, 07:46 PM
Hi Nicole, Welcome aboard. ;)

There are thin sets that are suitable for going over cutback. How large of an area do you intend to tile?

01-07-2003, 09:58 PM
thanks for all the comments! i searched the term cutback and found tons of other threads similar to my question.

i'm doing about 375 sqft of entryway, hallway, kitchen, and utility.

is a concrete-based underlayment (that would also help me level the floor) by someone like ardex not a good idea before i put down a modified thinset? or should i just go with the modified thinset right over the mastic? thanks!

01-07-2003, 10:08 PM
The ardex is not required unless you have areas to level out. Don't use it if you just want to cover up the cut back adhesive.

Versabond is a good thinset ; Flexbond is even better


01-07-2003, 10:22 PM
is it kosher for you to tell me what specific thinset you would use in this case? i've looked at versabond, flexbond, laticrete, mapei, and summitville online... i'm a newbie and need some direction as to which product you would suggest.

Sonnie Layne
01-07-2003, 10:34 PM
Everything's kosher (well, maybe not technically) here.

Custom's Flexbond is good. I've used Laticrete as well, but I forget the number, it's the most expensive whatever number that is. I used Mapei once and found it a bit coarse, but I'm certain the holding capacity was more than adequate.

There again, I'm not John... haha......John???

01-08-2003, 06:55 AM
Nicole, this site is not sponsered by any of the tile product manufacturers. If someone recommends a product by name, it's an honest recommendation, not a paid endorsement. Ocassionally, you will see someone trash a particular product, again an honest opinion. Feel free to talk about any product you want, someone will have an opinion, one way or the other.

Back to your floor, does it need leveling? The rule is the floor should be flat (not necessarily level) with vertical deviations less than 1/4" in 10 feet in any direction. If you had a 4 foot level, lay it on the floor and measure the low spots. They should be less than 1/8". If all you have is a couple of high spots, you can knock them down with a scarifier and patch the area if necessary.

If your floor is simply sloped in one direction, that may be OK. Just ask yourself if you noticed it before, then you'll notice it after tiling.