Hi, I am putting in a Kahrs woodloc floor. It will be placed on a 1/2 plywood floor that has 5/8 particle board on top. My question is that I have some dips and such between the existing joist and I know I can't use SLC(self levelor) on top of the particle board, so I was wondering if I could use something like drywall wall joint compound, or even a cement redimix on top of tar paper to level up the low spots vs using shingles or tar paper. I did a previous room using tar paper, etc but I feel I could get a better job "scrreding" the compound over the low areas.

Thanks in advance,

ps
I was going to put down tar paper and put the compound on top of that so the moisture doesnt go through to the particle board.

thanks
gris

Those "fillers" and compounds don't adhere well to tar paper. If you've ever seen a tile setter do a "mud" job, they will first staple their paper down, then staple chicken wire or similar as reinforcement for their dry mix, which is a portland cement product. So, to answer your question, you can do what you propose, however, it will probably not adhere to the substrate. If you want to "screed" a filler across your low spots, consider ARDEX Feather finish, which is made for your situation. I believe one needs to apply a sealer/bonding agent first when going over wood substrates. Check with a local flooring material supplier (distributor, not reatailer) for supplies. No tar paper needed with ARDEX.

Sounds good, will check for ardex and thanks for the reply.

Partical is not an acceptable subfloor no matter what you level it with. The moisture from Ardex will cause the partical board to swell. Is this a nail down or glue down? Partical board will not hold nails, and moisture in adhesive will cause it to swell. Tear out the partical board and replace with plywood.

tandyr, its a floating floor. Particle is acceptable for that. I did 3/4 t/g in other rooms of the house already and removed the particle board and installed additional layer of plywood for that, but the wife wants this Kahrs floor in, so it is easier to deal with since there is no tearout involved.

I'm sorry I did not pick up on that. However, try everything possible to level the floor with something other than a moisture based product. There are some great installation technicians (they are more than just installers) on this board. Maybe they will help both of us with some way to shim low spots without getting the p/board wet.

tandyr, agreed. I checked the supplier around here and for what they want for ardex, I can just use some shingles or some scraps of luan to fill in the low spots. May take a little longer, but like you said about the moisture, heck that is why I am putting in hardwood vs carpet, my dog(unbeknowst to us) was using some of the carpeted rooms as her personal bath.

gris