As the title says I’m completely new to doing my own home repairs or construction. I’m planning on laying LVP, upon removing the carpet I noticed water damage and had to cut out MDF underlayment. I can’t find a replacement sheet to patch what I’ve ripped out. A friend suggested to buy OSB instead since it would be under the LVP anyway. The MDF underlayment is 5/8, the only OSB I can find is 19/32. Would it this ~5% difference throw off my floor significantly enough to notice? I should also mention the areas in question are at the far end of a room where it won’t be stepped on almost ever. Thanks in advance for any advice!

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Kristen242 t1_je7fmjf wrote on March 29, 2023 at 11:20 PM

#2,465,375

MDF for flooring is horrendous and I would replace with OSB anyway. You have two options, use something slightly thinner and shim it to the right height. Or use something slightly thicker and route channels in the OSB where required to take it to the right height.

Dwindling_Odds t1_je7w9fx wrote on March 30, 2023 at 1:24 AM

#2,468,931

Yes, the height difference will make a difference. Definitely fix that before you lay the finished floor or you'll feel it every time you step on it. But it's easy to fix. Just use some strips of heavy paper or thin cardboard on top of the joists and then screw down the OSB on top of them. As many layers as necessary to make up the difference.

icetfupson89 OP t1_je8e41s wrote on March 30, 2023 at 3:50 AM

#2,472,958

Replying to Dwindling_Odds (#2,468,931)

Good idea

tired_and_fed_up t1_je8ec2g wrote on March 30, 2023 at 3:53 AM

#2,472,996

OSB is for subfloor and MDF is for underlayment. If you can't get 5/8" MDF, then consider getting 1/2" MDF + 1/8" hardboard. You can use OSB but I would personally go sanded plywood. Same thickness and shim it up using chipboard or similar so that its at the same height.

While the 5% difference is barely noticeable, for LVP and similar flooring options, it will be a pain to install and will crack over time.

DeVonSwi t1_je8utgn wrote on March 30, 2023 at 7:02 AM

#2,476,458

MDF (particle board) should never be used for floors (or anything for that matter). Particle board will swell and break up with any moisture. I would suggest plywood (OSB as a second choice) and yes the 19/32 would be fine as a replacement.

bad2behere t1_je92mov wrote on March 30, 2023 at 8:57 AM

#2,477,784

Replying to DeVonSwi (#2,476,458)

I'm not a professional, but I was taught by one and have helped do the work on every home we've repaired/redid for 52 years. @DeVonSwi is right. Plywood instead of particleboard is definitely the way to go on flooring. I've seen particleboard fall apart far, far more often than plywood. Shimming is also the way pros used to level things. Cardboard shims disintegrate faster than wood.