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I am looking to convert an old garage into a workspace. The total concrete area is about 20ftx22ft, and has one seam down the center. The pad on the north side of the seam is level. The pad on the south side has a grade from settling after 60+ years. It averages a downward grade at about 1.25 inches over 9 ft. I am going to be putting LVP down eventually, so I need it moderately level, and have been trying to think of a cost effective way to fix the slab.

The first option I thought of was self leveling concrete, but the amount of material that I would need would come out to $1,600+. Which is a lot of money that I don't really want to spend.

The second option I thought of was to put down OSB on one side, and then build tapered joists for the grade side, but I probably would want to put some type of dimpled plastic membrane down? I am not too concerned about water leakage, but it is probably something that most people would recommend.

Another option is to use Dri-Core, but can I shim that much of a grade to level?

Are there other options I could do? What is the best way to level such a large area with that deep of a grade?

  • LVP may not work well across that seam. – Jasen Aug 30 at 4:25
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If you don't need all the vertical space, two options come to mind.

It would take about 3 yards of concrete to "top" that whole slab with a couple of inches of normal concrete, preferably fiber-reinforced. That won't be in danger of peeling off. However, if your concept of a workspace is LVP floored, the (presumed uninsulated now) concrete slab will be directly coupled to your floor, and that may be unpleasantly cold much of the year, and damp when it's less unpleasant that it's cold. Good if your workspace concept benefitted from a concrete floor, probably bad otherwise, and you seem headed for otherwise.

If raising the floor on sleepers, I would suggest raising the whole floor and insulating under it, rather than laying OSB directly or with moisture barrier (only) on the concrete on the "flat" side. That will give a floor that most people would consider to be more pleasant to live with, and may also reduce your heating bill somewhat, if you are in a climate that involves heating bills.

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  • I am concerned about loosing too much height, if I were to use the fiber-reinforced concrete to level it better could I put like a some type of insulating moisture barrier with 1x4 sleepers and a thicker OSB? – SenSok Aug 30 at 14:15
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conrcrete with fine agregate where thicker than 1/2" mortar where it's thicker than 1/4"
self-leveling where it's thinner (and any low spots left over from steps 1 and 2)

before starting de-grease, clean and etch the slab, apply a concrete bonding glue.

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  • But wouldn't that eventually pull away from the slab? And be worse off than before? – SenSok Aug 30 at 4:57
  • done right it will last a long time... the slab may continue to settle, that will be a larger problem. – Jasen Aug 30 at 4:58

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