Hi, I am going to install 3/4 solid maple flooring. I have read the posts regarding these topics but have some specific questions.

My subfloor is 2x6 TG solid wood and there is a 1/2" Potlatch floor underlayment on top of that. My questions:

1) I have been told that there a difference between "particle board" and "floor underlayment" even though they appear similiar. Is there a difference? And, if so, can I install the hardwood over the "floor underlayment?

2) How "smooth" does the subfloor need to be? The home is new construction and I saw the subfloor before the underlayment was put down, there are heighth differences between the subfloor planks all over the place usually 1/8 inch but in some places probably a 1/4"? If I have to tear up the underlayment, what is the best way to smooth out the sub floor. Sanding and planing? Or, spend the time and $ to put down a new layer of plywood?

3) If I would only be putting down an underlayment to smooth out the surface, what is the minimum ($) that I should use? Won't the nail or staple reach through to the solid wood anyways and have a good solid grip there?

Thanks for any help you can give,

Darin

A subfloor built of 2x6 solid T&G wood is rather unusual today. In the 50's and 60's, we saw subfloors built of 1.5"x5" T&G Fir installed 4' oc on 4x6 beams. Occasionally, someone will choose a 2x6 V-groove pine plank installed on a second floor and have the floor boards exposed to below for a wood ceiling but that isn't the norm. Typically, when a solid board subfloor is installed, it is a 1"x6" non T&G plank run diagonally across the joists. This is an excellant subfloor, if done properly. I suspect that if you truly have a 2x6 T&G subfloor, those planks span 4' across support beams. You can approach this a couple of ways.
1) The underlayment needs to go. Potlatch is merely a brand of particle board and is not recommended as a wood floor underlayment.
2) The smoother and more even the subfloor, the better the installation. You can sand the subflooring down to level it. This was commonly done decades ago when solid subfloors were more common and is still done today as needed.
3) If you do not wish to sand the subfloors, then I recommend a minimun of 3/8" CDX grade plywood stapled down. You can glue and screw if you wish instead. 1/2" would be better and only cost a few bucks more per sheet. This will provide you with a smoother substrate to install the wood flooring over, provide more rigidity and strength to the subfloor and allow you to run the wood flooring in any direction you wish.

Thanks for the info. The 2x6 T&G subfloor does span four foot beams and it runs perpendicular to the direction I am planning on installing the floor.

Also, is there any benefit to glueing and screwing the plywood underlayment vs. staples?

And, a large section of the current underlayment was put down under linoleum and I believe it was glued, any advice as to the best way to remove it? Or is it just a piece by broken piece job?

Thanks again, Darin

If I can get the 2x6 subfloor smooth enough, would there be any benefit to having the plywood underlayment, vs. direct install over the subfloor?

Not in my opinion.


Installing additional plywood will stiffen the subfloors which decreases deflection. It will also aid in stabilizing subfloor movement. It will make for a better floor but you need to check for height clearences of doors and appliances