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Underlayment help- spacing/screw pattern

7444 Views 2 Replies 3 Participants Last post by  JazMan
Hello, I own a 1,200 sq ft home (built 1954) in southern CA. I have a raised foundation with diagonal subfloor planks (maybe 5/8) that set on 2X8 joists that sit 16 on center.
I plan on running 3/4 tongue & groove plywood over that as underlayment for the luxury vinyl planks (with the cork backing attached). The I will screw them down with #8 1 3/4 subfloor screws. The problem is I'm hung up on the spacing and screw pattern.
I've seen videos where I saw the guys just pound the t&g together, yet I hear you have to leave a 1/8 gap between all the boards, as well as a 1/8 - 1/4 inch gap where the boards meet the walls. As for the pattern, I hear it's 3/8 from the edges (which seems too close to me), and every 3 inches all the way around the board, then every 6 inches in the field (the middle).
I also saw info that said if I'm using vinyl, to use a fan pattern over the typical grid pattern (to prevent imperfections from showing through. I'm also wondering if it's cool to use wood filler on the inset screws to make a flatter/smoother surface.
Thanks in advance.
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Not sure where your getting any of that info.
I'd be using Advantech not plywood, it's stronger, cheaper, no voids in the plys, 50 year warranty.
It's made so there's a built in gap.
Screws will cost 3 times as much, take far longer to install and leave you with raised areas any place the screw goes in.
Constrution adhesive on the joist and 8D ring shanked nails with a framing nailer is the way I'd go.

Not that it really matters that much now, but I doubt very much your subfloor is only ⅝" planks. I'll bet they actually measure at least ¾" and maybe ⅞"

There is no reason to use t&g as an underlayment. Why do you think you need t&g? T&G sheets are subfloor, not underlayment grade.

Looks like Joe assumes you're installing the new t&g ply over the joists and is why he said to use construction adhesive. You're not doing that.

Your fastening schedule is all wrong for ¾" material, you're referring to ¼"-⅜" ply/OSB fastening. Underlayment is always square edge and should be spaced ⅛" when using thicker structural ply or OSB. However please read the instructions that come with the flooring because you're doing a different method than what most people need. In most cases the old subfloor is already structural ply, and all you need for vinyl is ¼" ply that meets certain specs. So check the instructions.

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