Within one 4x8 T&G plywood sheet subfloor, about one third of this sheet was water damaged and need to be replaced. I have the following questions :

1. do I just replace the damaged area or replace the whole sheet?
2. if replace the whole sheet, how difficult to get it out from the adjacent sheets, since they are tongue and grove together?
3. if replace the whole sheet, how to put the new T&G sheet in? As there is no space to slide either side of the existing plywood to make room for the new sheet.

I would appreciate if anyone will share their opinions and experience what would be the best way to handle this situation.

 

You have to buy a whole sheet anyway, so let's just replace the whole thing. Make cross cuts in the offending piece in both directions with a circular saw and remove the pieces, nails and scrape the glue off. On your new piece, use your circle saw to take the bottom lip off the groove end. Now, you can slip the tongue into the adjoining groove and the end where you cut off the bottom part of the groove will fall down onto the other. Be sure to use an adhesive and ring shank nails or screws to secure the new piece in.

 

How large is the damaged area? You can buy quarter sheets of plywood. They won't be T&G but I don't think that's important in a small area. Just be sure that the repair edges end on a joist.

I hate humping full sheets of 3/4" anything.

 

Make sure the plywood spans at least 3 joists. Spanning only two will allow it to bow down. A quarter sheet would do that lengthwise, not sideways.

 

You mentioned "Make cross cut in the offending piece", do mean cross cut diagonally in the offending piece?

I just measure the width of the existing T&G plywood in my subfloor, they are all 47.5" across the surface without including the tongue! However, the lumber yard that sells this 5/8 T&G plywood is 48" wide across the surface without including the tongue. Why there are different width? Does anyone come across this problem?

 

"cross cuts".....across the grain and with the grain at 90 degrees. It is easier to remove pieces than it is an entire piece of 4x8. Your flooring may have shrunk over time, or it could have been a mill error. Nominally from edge of groove to flat before tongue is 48", but it can vary a little.

 

I did go to Home Depot last night and measured the 3/4" T&G plywood and its width was 47.5" but the 1" T&G plywood and its width was 48". It did not have 5/8" T&G in stock.

Do anyone have an experience and knowledge about this different in plywood width?

Thanks!

 

You're worrying about the wrong thing. The 1/2" width can be split between the two edges, leaving only 1/4". You will most likely be using the 3/4" anyway, so why measure the other sizes? Gotta get busy with the floor!

 

My house was built 31 year ago. The subfloor is 5/8" with slightly sanded surface and measured across the surface width is 47.5" (the tongue is inside the adjacent sheet, so don't know its width). How to handle this 5/8" T&G plywood that is 48" width across (without counting the tongue) into existing the existing 47.5" width? Do I cut the tongue side or the grove side or split it into 2 halves in order to reduce the wide down to 47.5"? I would like to get this done this weekend.

 

Cut 1/2" off the groove side. Break off the tongue on the good piece adjacent to where you will be installing this one, glue it down and nail or screw it down.

 

OK, I can do that. Do I need to space out 1/8" on the side where both tongue and grove get cutoff? What about putting extra support underneath the side where both tongue and grove get cutoff?

Thanks for your advices, really appreciated!

 

You're not cutting off the tongue of the new piece. Use it. The only thing you are doing is accommodating the edge that will butt against the groove edge of the new piece. Removing the tongue of the existing piece will allow you to lay down the new piece flat without restriction. Extra support is not used now, why would it be necessary with the new piece? You can do it if you like. Weekend starts this evening

 

"What about putting extra support underneath the side where both tongue and grove get cutoff? " -------- Yes, you need it if you cut a part of a groove or the tongue off a sheet. That is why they are there. Installation instructions also require glue in each t&g joint. This is to get the required shear flow of the product for racking strength. If you cut a t- or a -g, add blocking under that area and nail or screw it 3" on center there. This is especially important because the sub-floor is acting as underlayment also. Not to worry about the gap as it is self-gapping. (the tongue being longer than the groove). Are you sure it isn't 19/32"? That would be the standard 5/8" strong or 3/4" shy. I've never used 5/8" T&G.

Be safe, Gary