Forever_Remodeling

Remodeling my 1st floor powder room. Gutted everything. The floor is 3/8" plywood subfloor. Wall plates etc built on top of that. Then there is a layer of 3/4" particle board. On top of that was 1/4" plywood underlayment that had the vinyl flooring on. I pulled the underlayment off easily. When cutting out the 3/4" particle board with my sawzall, I cut into the 3/8" plywood in a small area. The cut is between and parallel to the floor joists (16" oc). Do I need to worry about this since I will be putting down 3/4" plywood over top of it anyways? My guess is that the 3/8" plywood subfloor is simply a "spacer" to help the vinyl flooring match up to adjoining hardwood floors?

budro

make sure the 3/4" plywood you put down covering the two joists on each side of the cut is from one piece and you will be fine. squirt a bead of liquid nail in the cut to repair the damage. budro

remmons

X2.

Hopefully, you did not cut into the floor joist. If you did, you will have to call a Home Improvement Center or lumber yard for what's called a Joist Repair.

Forever_Remodeling

Thanks! Next question. The 3/8" subfloor that I mentioned goes under the wall plates. On one side of the room, the joist is located back under the wall plate. The next joist out is about 14"- 15" OC. But, from the edge of the bottom wall plate to the joist (the area where the 3/4" plywood would sit) is only about a 10" - 11" span. Is there any concern when I glue and screw in the 3/4" plywood since I won't be hitting a joist along this edge of the wall? I can't add any cross bracing, etc in this joist bay because ductwork is running in it. If I glue and screw directly into the 3/8" plywood, does this give sufficient support? The 3/8" is pretty solid in this area.

The plan is to glue and screw 3/4" plywood on top of the 3/8" plywood floor that runs under the walls. On top of this to add 1/4" cement board for tile. The powder room is about 4-1/2' x 5-1/2' in size. Goofy size. I cross braced in most places (especially under the toilet) to help solidify the floor, but my concern is a lack of a joist to screw the edge of the 3/4" plywood along the wall as mentioned above.

Jaz

You will not get much "bit" into 3/8" ply. for the new 3/4". Might be better to remove some of that 3/8", add blocking, put it back, then install the new sub.

Normally the new top ply (underlayment) is fastened only into the subfloor. In this case you should pretend the 3/8" is not there, except I would still add some screws between the joists.

Don't forget the thin set mortar under the concrete backer, tape joints etc.

Jaz

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Tile 4 You LLC
Troy, Michigan
www.tile4you.com

I've NEVER made a mistake....I thought I did once....but I was WRONG!

Forever_Remodeling

Thanks! Do I need to leave any sort of "expansion joint" for the 3/4" plywood? I will be using only 2 small sections (roughly 2'x3') with a seam down the middle of the room....this will run perpendicular to the 3/8" plywood. I did notice that the 3/8" does not have any expansion joint where it is butted against each other, so am not sure if the same holds true for the 3/4".

Lastly, when I install the 1/4" cement board, does the cement board also need to be screwed into the joists or just into the 3/4" plywood? I also will use thinest mortar between the 3/4" plywood and cement board, and stagger the joints --- although there shouldn't be no more than 1 or so.

Jaz

Yes leave about 1/8". Be sure to run the grain across the joists and it's best to hit at least 3 joists. So about 32" min. with 16" o.c.

Jaz

__________________
Tile 4 You LLC
Troy, Michigan
www.tile4you.com

I've NEVER made a mistake....I thought I did once....but I was WRONG!