subfloors for wood installation

Old 11-22-03, 08:31 AM
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subfloors for wood installation

Sometime ago, and I won't say how long because I'm embarrassed, I pulled up some of the carpet and particle board in my house to begin a hardwood installation. I received excellent advice from this forum, but pulling up the particle board was as far as I got.

I still have a some questions.

I have a plywood subfloor, approximately 1/2" thick. This is what was under the particle board. The recommendation I was given on this forum was to install another layer of 1/2" plywood on top of it. I also have some leveling issues.

Question 1: I received some conflicting advice about how the direction in which to lay the next layer of plywood. Should it be at 90 degrees (right angles to the old layer) or in the same direction?

Question 2: It was suggested that I use glue and screws for the second layer of plywood. I bought some tubes of construction adhesive. Is this what I need? And how long should the screws be and what type of screws do I need. Someone suggested 2 & 1/4" sheetrock screws. Lowes has 2" and 2 & 1/2" but no 2 & 1/4" screws. Do I go with the 2" or 2 & 1/2"?

Question 3: I bought a one gallon bucket of DAP flexible floor patch and leveler. I assume I should probably buy more of this stuff but this was all Lowes had at the time. There is also the powdered stuff in the bag that has to been mixed. I would rather avoid this. Did I buy the right stuff?

Question 4: Do I need the liquid mixer stuff that they sell to go with the DAP. There is a product for both the powder and the pre-mixed buket of DAP. It's supposed to make the product stronger, etc.

Question 5: Am I better off using the leveler, undercourse shingles, or #15 roofing felt when it comes to leveling the floor--or does it just depend on the situation? I want this job to come out right, but I also want to do what is easiet and the most simple.

Question 6: The CDX grade 1/2" plywood that I bought at Lowes was actually 15/32. They said this was their 1/2" plywood. Is this close enough? Also, at least one piece seemed to be warped. Will that matter once I screw down the plywood.

Question 7: Should I be using a thicker layer of plywood as the second layer (3/4" v. 1/2"). The original layer appears to be 1/2" and the aprticle board that I took up also appeared to be 1/2". I worry about some potential height issues, but if that is a problem, I suppose I could trim doors, etc. I have already bought about eight sheets of the plywood.

Question 8: I have a leak at my back door and have bought a storm door. Hopefully, that will stop the problem, but I am also having a screened in porch built. That should definitely stop the probem. But my real question is, should I pull up the water stained plywood? The home repair guy doing the other stuff around my house said it wasn't bad enough to woory about.

Question 9: I assume that I need to take care of the leveling issues before putting on the second layer of plywood or the leveling issues might be accentuated. Do you agree?

Question 10: I'm also afraid that I might have to pull up some original plywood and plane down the joists in a few spots. This worries me. Any suggestions abut doing this or just read my flooring book?

You can see from all of my worries that I probably should just hire someone to do all of this, but my wife thinks I can do it. Also, we have already spent enough money on other home repairs.

Thanks. Sorry so long winded. I off to drive nails down so I can sand high spots.

I apreciate any help I can get.

Old 11-22-03, 08:54 AM
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subfloors for hardwood installation

Sorry folks. One more question. What is the level of tolerance for the subfloor when installing hardwood? It has to be level with what range over what distance?


Old 11-23-03, 05:04 AM
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Seriously it is suppose to be at 45, so the seams in the underlayment are not under a row seam.

Glue and screw will work. I like to use felt and screw. Why so long of screws? Maybe to hit joists but out in the field, you don't want the screws to go totally through both layers of plywood. They loose holding power when they bust through.

Never used the DAP product you bought. It may be good, it maybe junk?
I have always used Ardex products, that need mixing. Premixed stuff usually fails.

Liquid latex additive has been used for years now. it adds bonding and flexibility to the mortar. If the product is already latex fortified, don't add more!!

It will depend on a lot of things, but if the area is big and needs considerable work, self levelers are your choice.

I would use 5/8" plywood

Same answer as above.

Hard to say without seeing it. Is it too rotted to hold a screw?


You might be right. The flatter the subfloor, the better.

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