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Mjolnir 12-07-2011 08:22 PM

What should I do now with my subfloor?
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hello...i am trying to install a ceramic shower stall and ceramic floors on my bathroom. i demolitioned what i could so far and don't know what to do next with my subfloor.

initially, i wanted to remove the plywood subfloor and replace them with new plywood because they show some water damage but i don't think i can do that because the plywood are directly underneath support frame.

the original floors had tile, conrete, wire mesh, then plywood subfloor. i have aobut 1.25-1.5" from plywood subfloor to top of tiles.

i don't know what the best route is to fix the floor with plywood, concrete, backer board, etc... at this stage im open to laminate after seeing the water damage. any advice suggestions would be greatly appreciated.

NewHomeDIYGuy 12-08-2011 02:09 PM

If you cut out the plywood and find you have nothing to screw/nail the new plywood down to, you can "sister" (is that the correct construction term) some extra pieces of 2x4's or joists to the existing framing for the subfloor. If there isn't framing for the subfloor you can sister to, you have to frame out flooring to support the new subfloor.

If the subfloor needs to be replaced, rip out/cut out the damaged parts, look at what you have underneath, and go from there.

Mjolnir 12-08-2011 02:19 PM

ok thanks that was helpful, don't think i know how to sister...i think i will replace the subfloor. a guy at home depot said that wall is not a supporting column that it was ok to remove the plywood there and cut along the wall to remove other plywood.

i was thinking to waterproof the new plywood and surrounding wood with water proof sealer. is that a standard practice, does anyone do this?

Bud Cline 12-08-2011 02:20 PM

Your subfloor is fine, my God don't be thinking about opening that bag of worms for any reason. You are going to have a hard enough time just fixing what you have already started.:)

Now, What's this nonsense about laminate? What exactly is it you are going to do in this area? Are you really thinking about trading a quality tile installation for cheap laminate?

Big Stud 12-08-2011 02:31 PM

Listen to Bud. That plywood looks like it is just a bit water stained, not rotted. To tell if it is rotted, poke a screwdriver into it. If the screwdriver doesn't go through the wood easily, it is not rotted badly. Replacing your subfloor is a lot of work. You should let the plywood dry out for awhile and go ahead and retile it. Mabey ask Bud how since he is a tile guy,

Mjolnir 12-08-2011 04:27 PM

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thanks for your comments, they could save me lots of time and energy.
here is a better view of the weakest part of the floor. you still stand on your original statements?

the ultimate goal is tile shower stall,tile floor, new commode, sink, glass shower door. but after seeing the floor lost some confidence in the waterproofing of this setup as it was the original. that's why i was thinking of laminate.

i was thinking of putting another layer of plywood to strengthen the subfloor, good or bad idea, then backerboard n tile.

also you see the width of the shower stall. how far should i tile up, ceiling, below shower head, above shower head. i want a nice proportion of width to height.

Bud Cline 12-08-2011 04:40 PM

How thick is that plywood?

Mjolnir 12-08-2011 05:05 PM

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looks like 0.75" thick plywood and 1.25" from plywood to tile. is thinset is 1/8" and tile 1/4"? so i have more than 1/2" to work with?

Bud Cline 12-08-2011 08:21 PM

I think if it was mine I would peel some of the loose and shedding wafers and then cover the whole floor with another 1/2" of plywood to clean it up.

First use a screwdriver and poke around the worst areas a few times and see if what remains is solid.

Typically I wouldn't tell someone to use construction adhesive when installing a second layer of plywood but in this case I think I would use construction adhesive and screw the new plywood about every eight inches in both directions. If you add new plywood use "underlayment grade"-"exterior grade" plywood. Not treated and not CDX, "underlayment grade".

Mjolnir 12-08-2011 10:21 PM

ok thanks i'll do as you suggest. do i need to use leveling compound on the existing plywood before adding the 0.5" plywood?

Bud Cline 12-08-2011 10:25 PM


ok thanks i'll do as you suggest. do i need to use leveling compound on the existing plywood before adding the 0.5" plywood?
Nope that won't work. That's why I suggested the construction adhesive in this case, and don't be afraid to use plenty of it. Before you do anything poke around with a screwdriver and see what happens.

Mjolnir 12-10-2011 02:43 PM

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im almost ready to do as you suggest. after removing the toilet, i see the floor is a bit damp i am waiting for it to dry out before i proceed. one question, i guess to do a proper job i would take out the toilet flange before adding 0.5" plywood? or should i try to carve the plywood around the flange?

if i remove the flange, and put on the tiles how high should the sewer pipe be relation to the top of tile. what if it's too low or high?

Bud Cline 12-10-2011 02:50 PM

Don't screw around with the toilet flange, you are already in over your head. There are ways to deal with the flange later. Wait and see where it ends up and then deal with it.:) "Carve" the plywood around the flange for now.

Mjolnir 12-13-2011 11:41 AM

home depot is my only option for plywood. i do not see 1/2" underlayment grade plywood, what do you suggest?

Bud Cline 12-13-2011 11:52 AM

Exterior Grade B-C Exposure 1.

Nomenclature is sometimes regional. It's there.

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