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In my basement I removed old carpet planning to install LVP, so I need to flatten out the slab a bit. The carpet left a thin glue residue over the entire floor that I've been trying to remove before pouring self leveling cement (pictured below). Picture of glue residue

It's still tacky with enough weight, but otherwise dry. I've tried to scrape it off, but can't really make any head way. I've tried boiling water, a heat gun, and a couple solvents but all failed to loosen it much. The only thing that has worked is a cup wheel concrete grinder, but it gets gummed up really quickly.

So my question is, if this adhesive is so hard to remove from the concrete that I need to take some concrete with it, can I just use the self leveling primer over it and then pour like you would for concrete with well-adhered paint? What would be the possible consequences of not removing it?

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    You might want to check with the manufactures of the leveling cement you plan on using .There are many different kinds. Also read the directions for surface preparation on the product you want to use.
    – JACK
    Commented Nov 3, 2022 at 15:15
  • Sure, I've looked at several and most say some generic form of "free from contaminants". But one also mentions that non-water soluble adhesive can be scraped "to a thin layer that appears to be no more than a stain". Since water's had no effect and it's really thin I'm thinking that this glue would qualify even though it's still sticky?
    – AJD
    Commented Nov 3, 2022 at 21:35

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Self levelling cement needs to bond tightly with the substrate it is applied to. Since the layer is usually thin, under 1 inch, it achieves its strength through the bond with the substrate. Without such a bond the cement will eventually laminate, i.e. separate from the substrate and crack & crumble through mechanical stresses from dynamic loads (e.g. walking) applied to the flooring on top of it.

Some variants of cement may be able to bond to a wide variety of substrates due to additives such as polymers. Thinset for tiles is a good example, but thinset is covered with tile (of course) and the total assembly will have sufficient strength. Some cements allow or require pre-application or mix-in of a primer for this reason. Even if the bond to the glue is strong, you still have to ensure that the glue will remain bonded to the concrete floor with sufficient rigidity to provide the support that the cement needs.

I would check with the manufacturer about your specific case, but I fear that the correct procedure will require you to scrape off the glue first. For this you'd buy a rake style concrete scraper, or rent a machine with rotary scrapers.

As an alternative you could opt for felt or tar paper laid down in the low spots.

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  • Could felt or tar paper survive being fully submerged? I want to make sure everything is water proof and won't grow mold in case of any basement flooding.
    – AJD
    Commented Nov 7, 2022 at 3:00
  • there is mold resistant felt, tar paper resists water, but if you are worried about fully submerged basement then LVP is also a problem because of water trapping and no evaporation. What's your underlayment?
    – P2000
    Commented Nov 7, 2022 at 4:27
  • The underlayment is an integrated closed cell IXPE foam that the manufactured claims to be waterproof.
    – AJD
    Commented Nov 7, 2022 at 14:55
  • Ok sure, that's good. Now continue the thought: how are you preventing water ingress and retention between layers of LVP, IXPE, and concrete? The point I am making is that we accept these risks, and adding tar paper or another hard to compress layer in the low spots falls under the same risk. To really solve such a water problem you need to tile the floor, or install a breathable subfloor with drain.
    – P2000
    Commented Nov 7, 2022 at 18:10
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Since the glue is non soluble with water and very thin you can use a leveling compound after applying the recommended primer. Or your could put down an underlayment pad that will make the basement floor a little less cold. There are a few underlayment's that are recommended for LVP. I have used QuietWalk Plus with great success. 43 cents/sq ft. @ HD and Amazon.

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