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Working on a basement remodel and getting to the point of needing to figure out flooring. Unfortunately, the concrete slab is generally uneven. I had a company come in and grind the floors a few months ago. While they did a great job of making the floors WAAYYYY better than they were, the floor is still not flat enough for any type of floating floor installation like LVP. I bought a box of LVP from a local Floor and Decor to test out install on the uneven floor. The LVP does a decent job of conforming to the unevenness, but there are still some areas where you can notice the dips in the floor and the LVP will bow in these dips. This is less than ideal, so looking for some options or insight into what can be done for flooring. I put a bunch of ideas that I've had below, but wondering if the DIY forum has any additional brainstorm ideas.

LVP or any vinyl generally seems to be the preferred material due to its water resistance for a below grade application. Open to suggestion on this as well.

Options to Work Around Uneven Concrete Subfloor

  1. Glue Down Vinyl - Find some glue down vinyl planks from companies like Flooret. Pros: Planks will conform to slab the best, most solid install method. Cons: Finish options are more limited. LVP [Option 1] - Use regular LVP and glue this down to subfloor. Companies like Titebond make an moisture barrier adhesive for flooring, so seems like it could work. Pros: Lots of flooring choices. Cons: Will it actually work?

  2. LVP [Option 2] - Use regular LVP and shim low spots as needed using floor patcher, shingles, etc. Pros: Lots of flooring choices. Cons: Giant PITA to shim everything. Cost for floor patcher, shims, etc.

  3. Concrete Screeding - Use concrete to screed out the current slab and get rid of the remaining height variations. Pros: Get a nice flat subfloor. Cons: Very expensive $$$$, better for professionals.

  4. Plywood Subfloor - Put down vapor barrier on slab, and place 3/4" plywood over . Seen a few other suggestions of using 2 - 1/2" plywood sheets and orient them 45 degrees off each other for stiffness, then screw together. Would probably still have some unevenness, but the plywood would ride over some of the imperfections better. Could secure the plywood to slab with Ramsets/Tapcons. Pros: Flatter subfloor than current, though not perfect. Cons: Some additional cost but DIY-able. Takes away from ceiling height, but 3/4" loss seems like a fair tradeoff.

  5. Sleepers/Plywood Subfloor - Scribe some sleepers on the floor. Pros: Can get flat subfloor. Cons: Cost (plywood + PT lumber), time, takes away from ceiling height

  6. Concrete Stain - Embrace the floor that's there and stain it. Use area rugs to cover up main areas. Problem is the current concrete isn't visually great. Would still require some patching (there is an old 1 inch wide trench from BX cable that used to run to an oil tank)

  7. Epoxy Coat - Embrace the floor that's there and epoxy coat. Would require some concrete work to patch some holes/cracks. Pros: Embrace the floor that's there. Cons: Cold floor, epoxy isn't my favorite look, requires some additional work but not super hard/expensive. If you want a better looking floor, may need pro install.

Additional notes:

  • There is a general slope to the floor where it drops about 3 inches over a length of 30ft. (house is 100+ years old). I could use self-leveling compounds to make this up and get the floor level & flat, but that would just be a huge cost to do this.
  • Ceiling height is limited. Current ceiling height is 7ft, just meeting code reqs. Any solutions that add height to floor I am less inclined to look at.
  • Basement is very dry. Its mainly above grade except for the back wall (house is built into hillside). Also had a french drain installed so any water that happens to get through is drained out through front of house.
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  • These are all viable options. Unfortunately, picking one over another is a matter of opinion, and that's off topic. – FreeMan Mar 31 at 17:54
  • I used your action plan list point 6 in my basement, only flooring/patch the areas by usage. – r13 Mar 31 at 17:54
  • @FreeMan had a more in depth discussion with an applications person at Flooret. He mentioned that their adhesive they sell is pretty aggressive. Even though they specify in their info pamphlets that the flooring spec is flatness within 3/16" or better, he said they've worked with installs with wavy floors. The adhesive does a good job of making the boards conform to the substrate. That also may just be marketing talk, so taking it with a grain of salt. But if true, this seems like the best option. – chienandalucia Mar 31 at 19:56
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Another option:

Self levelling low-spots only, and optionally adding plywood to smoothen the rest.

"self levelling" cement is not liquid as you think and you can apply it in patches without worrying that it will run like water. You have some troweling time to work low areas as large as say 5x5 ft.

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