I had to replace my 3/4 tounge in grove underlayment on the second floor of my home due to ductwork. I installed new 3/4 non-tongue in groove (it was too hard to match the old tongue in groove) plywood. After walking on the subfloor for a couple of days, I am noticing a lot of voids in the plywood which is causing cracking. Should I have used OSB instead? Should I remove the underlayment and install OSB? I have 2 x 12's at 16 inch centers.

Thanks
MBA

You must mean T&G subflooring to expose the joist. Whenever you cut out subflooring that runs underneath walls you have to install blocking where the new subfloor and old subfloor meet and nail or screw both to the blocking.

I actually did this. The voids I was referring to are in the plywood itself. If you cut a cross section of the non-used pieces, you can see voids all over the place. From other sources, I have found that cheaply made plywood is pretty much the norm. Is OSB a better choice? Should I remove the plywood and install OSB or can I install a 1/4 inch OSB over the plywood I already have in place (I glued and screwed in the 3/4 inch plywood)

Thanks!
MBA

That sounds like you have a CDX grade , used for sheathing and with many voids in the inner plys. I would suggest either a 3/4" AC or BC grade plywood which has no voids or AdvanTech OSB . You would have to cut off the tongue using AdvanTech.

Thanks Jerry - that is exactly what I used. Funny - I asked the guy at the local lumber yard (not Home Depot) and that is what they recommeded.

Now all I have to do is remove it and put in the right stuff before I can installed some decent hardwood floors.

M

Are you talking about the "football" voids?


CDX Is what I go over all the time.

No Perry, those are patches on the C side. The voids (holes) are in middle plies of CDX plywood, a high heel can punch right thru the C side if there is a void underneath. CDX is actually a sheathing and not intended to be used as a single layer subfloor.

A subfloor or underlayment grade of plywood such as Group 1 Underlayment, AC, BC will not have the voids in the inner plies like CDX does.

Ah, I missed the single layer of decking/subfloor. I was thinking underlayment.