heat gun?

If I use a heat gun (or hair dryer?), do i need to be concerned about flammability? I don't know if the glue is oil or water based, and I know that a ton of solvents have been used to get what's off so far. How can I try it without igniting a fire? I am desperate.

I hear your pain. No easy way. At least now you know how hard flooring people work. I worked floors for 45 years and I know how brutal it can be if you don't have great tools.

Solvents will drive the adhesive further into the concrete. I suggest that you consult with concrete restoration people or you will be struggling for a long time trying to get that slab back to a condition where you can then think about installing a new floor. Since I cannot see exactly what adhesive was used and what is left on your slab as residue, I cannot give you meaningful consultation.

Concrete restoration specialists will have the equipment that will make short work of removing the adhesive residue and scarifying the slab. That is the best I can offer for advice.

Good luck.

I'm confused. There was a pad glued to the slab and the wood???? Why would you do that? If the pad were plastic based, it might not ever let the glue dry. Especially in the presence of moisture in the slab.

Mechanical means are the only way to do this. Solvents and other chemicals will compromise the ability of the slab to ever have anything attached to it again.

Engineered wood is installed on concrete slabs in a double glue-down method. The pad is glued to the slab (both serving as a vapor barrier of sorts) and then the wood is glued to the pad. In my case the floor failed because of moisture, and now I am left with the nightmare of removing the whole mess. Now I am nervous when you say the slab may be compromised permanently. What does that mean??

Although you are taking this on yourself, because you had moisture issue...even with "a vapor barrier of sorts"...it may be wise to consult with a real professional who knows how to clean the slab, correct the conditions that led to the moisture problem and then get the slab into a condition to accept a properly specified and installed vapor barrier.

We have addressed the problem of water entering the walls and foundation by having new footing drains installed, the ground sloped away from the wall, and foundation walls sealed. We are getting a gutter. We have inspected and cleared all sewer drains. Nevertheless we will not be trying another wood floor on concrete partially below grade because it's just too risky. I now understand that between condensation in the room (there is no AC) and absorption of moisture in any old slab (pre-moisture barrier UNDER a slab, which is now mandated), will also present a risk. Thank you glenn for bringing to my attention the need to consider a vapor barrier under the next TILE installation. We have a tile installer coming in the am to give an estimate, so I will be sure to discuss it with him. Hopefully he will know who can take care of the glue removal too. Mechanical removal (scraping) wasn't working because the glue is sticky.

There are trowel on moisture barriers, but a glue on pad??? Beneath grade? Wood and laminate really are never successful below grade when there are moisture issues. This sounds like a non standard installation.

If you drive that glue into the slab by using solvents, you run the risk of not having tile stick to that slab. Or anything else. A floating floor may be the only thing that's left you at that point, and again, even with your moisture issue "corrected" you may have issues with those below grade.

You REALLY need an expert in there at this point. One of those flooring removal machines first, and then something to sand off the top layer that's contaminated with glue will be needed. If you've already contaminated the concrete further than just the top layer, you may have to remove the slab entirely and repour if you want tile. But, at least that approach would give you the opportunity to address the moisture issue properly from the ground underneath the floor up.

The tile installer who just stopped has a machine to sand off the glue. He also recommends putting down Vitra Mat (?) as a vapor barrier for the tile. Thanks for the warning about the solvents, as I will cease and desist that approach. What do you think of boiling water?

Have a GOOD tile man "scarify" and remove the glue. Do NOT use solvents as it will penetrate the slab. Install something like Schluter's "Ditra" and tile it and sin no more....

Ditra is a great product, both as tile underlayment and waterproofer (if seams are taped).