Glue-Down LVP in Basement. Anything BUT a straightforward install. Any help is appreciated.

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Boston_Engineer

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Joined
Feb 9, 2024
Messages
2
Location
Boston, MA
My home is 100 yrs old. I'm remodeling half of the basement. It's appx. 200 sq ft. The previous homeowner put down DRICORE and then did carpet on top of that. I tore it all up, revealing the concrete slab, half bare, half covered in black mastic(non-asbestos) from an old tile job. The old adhesive is not water soluble and it's very thin. It's mostly scraped down to a thin residual layer, and very well bonded to the slab.

The basement is almost 2 inches out of level over almost 20'. The perfectionist in me wanted to level the basement, but it would have been very expensive, and we're probably going to gut the house in 5 years or so. I just want a nice place to watch movies for a few years. With that said, I decided my goal is to simply flatten the floor as much as possible, and glue down some flexible LVP to keep this inexpensive.

A lot of research about how to tackle this led to this plan:
  1. Put down a layer of Laticrete Prime-N-Bond to cover the black mastic/concrete and create a bondable surface.
  2. Run a skim coat of Laticrete NXT Skim Lite to flatten the floor enough that the floor will adequately support flexible glue down LVP.
  3. Glue down some "DuraDecor Polished Pro Silver Linings 20 MIL x 6 in. W x 48 in. L Glue Down Waterproof Luxury Vinyl Plank Flooring."
My plan seemed solid until I started reading and thinking about moisture issues. While my basement doesn't have any visible moisture issues, I know some level of moisture(is vapor the right term?) comes up through the slab because I have a gym in the other half of the basement with those padded floor tiles. They were down for about a year and recently I lifted some up and there's visible light moisture on the bare concrete and on the underside of them.

My thing is, I'm having a hard time finding factual information to reference that pertains to my specific situation and gives me a solid path forward.

Questions:
  • Do I need to put some sort of moisture barrier down? If so, what kind?
  • Should the moisture barrier(I'm assuming it would be a liquid-applied membrane type of thing) be applied before anything else? or would it be okay to install it on top of the skim coat?
  • If I do need to install a moisture barrier all the way against the slab, is there any type of moisture barrier that bonds/works on both concrete and black mastic? Laticrete told me they don't have any product that can create a barrier over concrete and black mastic.
  • Someone mentioned to me that the glue can act as a moisture barrier. 1st, is this true? And 2nd, if it's true, won't I still be trapping a bunch of moisture above the slab and below the glue causing issues for my skim coat?
  • Am I just overthinking how the moisture will affect this?
I really need some help understanding what to do next. Thank you in advance.
 
I would say moisture testing is required before you consider a glue down product, especially if you’re just going to redo it in a few years. Save your money now and apply what you saved to doing it correctly later. Carpet is easy and will breathe. Loose lay carpet or carpet tiles are a couple more quick and easy option. You could plop down some vapor barrier then install a floating floor. How about loose lay vinyl.
 
Considering the very short term nature of this install I'd smooth out the floor with some patch and get some of the cheaper click-lock LVT. It's just got to be flat and smooth enough to keep the joints from failing from traffic and movement. Better types of underlayment (patch) have adequate polymers to bond and seal over any existing adhesive.
 
NXT self leveler might be your friend here.
Maybe not applied overly thick, just enough to get it smooth.
pour it on, but spread it from the deepest side towards the thinnest side using say.... A half in by half inch square notched trowel, the type for thinset. It would flow flat to 1/4 inch thick when all is said and done. Depending on the angle of the slope, 1/4 inch of self leveler wouldn't all flow downhill like a thick pour would.
...but yeah it will still want to flow.
...or half way up, the slope, switch to a 3/8 by 3/8 trowel
.....or do it all with a 3/8 by 3/8. I'm thinking if the notches apply just enough material so that they flow together, it will at least be smooth......
I believe however we'll this goes, you could finish feathering out from there with a standard patch.
I don't know if Latacrete has a moisture emissions type primer.
 

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