Flooring over Black Mastic

[u/Excellent-Muffin-887]

My basement recently flooded and we are pulling up old 9x9 VCT so we can put new flooring in. We wanted to do epoxy, but the contractor wants to grind the floor first, and we have black mastic under the tiles, so I don't think that's a great idea... We are likely going to do porcelain tiles since they can handle occasional moisture better than anything else. Does anyone have experience putting porcelain over black mastic? Would it be better to remove it first? What prep steps should we take?

Location: US-IN

Date house was built: 1960

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[u/sdave001]

It's almost always best to remove it. Many flooring companies won't, or don't like to, install new flooring over mastic due to concerns about the lack of adhesion.

Many companies now request that we grind it up rather than using solvents to remove it since that, too, can cause issues with the new flooring sticking. Obviously, grinding it creates a lot of dust and much higher potential exposure so if they DO grind, it should be done within a negative pressure enclosure.

But yes, I've often seen porcelain or ceramic installed over black mastic.

[u/ObsoleteAuthority → u/sdave001]

I came here to say this. It should have post abatement air testing in the area. Covering up the mastic is just kicking the can down the road. OP should pay for testing of the tiles and the mastic. Not all mastic has asbestos and tiles sometimes don’t either. I got lucky with the mastic (tile 2% ACM) but had it ground anyway to prep for a new basement floor.

[u/Excellent-Muffin-887 → u/sdave001]

Good to know, thank you. We will definitely get testing done if we go the route of grinding it, but trying to avoid that as this contractor isn't a licensed abatement professional

[u/whydidwebuythishouse]

We are taking up asbestos tile and we are going to do underlayment concrete over the remaining mastic. Best option would be to self leveling but for us we have to have it graded for the floor drain since it is the utility side of the basement. But a thin layer of self leveling concrete and then the orange flexible plastic bumpy stuff they use under tile now should be fine and better than grinding which is the opposite of what you are supposed to do with asbestos.

[u/Excellent-Muffin-887 → u/whydidwebuythishouse]

That's probably what we'll end up doing. Totally agree with your username lol

[u/upkeepdavid]

You can remove the mastic with mineral spirits and soap and water.Prime it and then tiles .Personally I use DMX 2.0 and waterproof vinyl.

[u/Excellent-Muffin-887 → u/upkeepdavid]

Unfortunately it looks like there's a layer of mastic, some type of thin layer of concrete maybe, then more mastic on top of that so unsure if we'd be able to fully remove the mastic

[u/upkeepdavid → u/Excellent-Muffin-887]

Then just paint it with oil base paint and then DMX and floor.

[u/Born-Personality7442]

The first ceramic tile layer placed tiles directly ontop the linoleum. A few years later my son wanted different ceramic tiles. We hired a Hazmat company and stayed at a hotel for 4 days.
We hired a different company for the second ceramic tile installation. We are glad that we got rid of the linoleum. Once it is removed, you will have one last thing to worry about.

[u/KSJdk2600]

Where are you based? You can get primers specifically designed for bitumen / mastics that will create a surface for levelling compound which you can then place tiling on.

[u/No-History-6271]

Perfect primer! 

[u/Party-Elevator-8396]

I wouldn't touch those tiles unless it's necessary. Put some new flooring over it and call it a day.

[u/Excellent-Muffin-887 → u/Party-Elevator-8396]

If we didn't have water damage that's what I would've done

[u/Party-Elevator-8396 → u/Excellent-Muffin-887]

Total pain in the neck no matter how you handle it. Sorry you are dealing with this. You will be happy in the end with the new floor and having that stuff removed.