Can I use a leveling compound over this glue?

Question

I have a large basement in a split level 1960s home with old 12 x 12 linoleum (likely asbestos) tiles on concrete slab. The total area is around 450 SF. I would like to put in a slate tile floor, ideally by leveling the floor then using Ditra. The linoleum tiles come up very easily without much fuss, so I don't mind donning a respirator and bagging them up for proper disposal. What worries me is the glue underneath, which also likely has asbestos in it.

Can I encapsulate it or cover it with a leveling compound? I need to level dips and imperfections in this floor anyway. Is there any product that will adhere to the old glue? I'd love to no have to worry about scraping it up.

Here's a close-up picture where two tiles came loose. I have done tile floors before, but never had to deal old asbestos linoleum this before this house. Any recommendations are appreciated!

Answer 1

The answer to your original question is no: this type of tile adhesive is known as "mastic" or "cutback", and if you carefully check the directions for most leveling compounds, they will specify that mastic or cutback must be removed prior to use.

That said, I recently dealt with removal of asbestos tile and there's two other approaches you could potentially take:

1. The mastic may not contain asbestos and can be removed with solvent and scraping. The only way to be certain is testing, so you should get the mastic tested. If clean of asbestos, you can use a combination of adhesive remover formulated for cutback and a mechanical scraper to remove it. This can be difficult if the underlying concrete was not flat. If the mastic does contain asbestos, you'll never get it off without it becoming friable and requiring extensive safety measures to legally remove.
2. Per FreeMan's recommendation, encapsulation is a much easier approach. Bury it tiles and all and never deal with it again. In this case, it won't matter if the mastic has asbestos or not.

Answer 2

I'm looking into the same sort of thing in my house, and as I was reading into the instructions for LevelQuick RS, it does specifically state in the instuctions that a suitable substrate is "Cutback adhesive residue." So if you prime the mastic with their primer and then pour the leveling compound over all the primed residue, based on what I am reading it would be an OK solution.

Also, since this is a fairly old post, if you have already taken care of this, what did you end up doing?

Edit: I mentioned this in the comments below, but if you read more into the instructions, the mention that the adhesive must be scraped off prior to applcation, which is confusing.