A toilet in an unused bathroom sprung a leak that went unnoticed until
carpet outside the door got wet. I've taken up the old tile, linoleum and
plywood. Under the plywood are diagonal boards (sub-subfloor?) over the
crawl space. After drying the room for a month I filled the termite-eaten
boards around the toilet with Bondo, and now I'm ready to lay down new 3/4"
ACX plywood. I'm new at this and I'm hoping someone will be generous enough
to answer a few questions.
The previous plywood had large gaps between it and the walls. Any reason for
this? I cut the new plywood for a tight fit.
There are gaps between the ends of diagonal boards that come together on a
floor joist. The gaps were filled with what looks like portland cement (?).
Wondering why filling 1/2" over a beam was important when some of the boards
are spaced wider than that. Much of the cement crumbled out when removing
the plywood. Should it be replaced?
The space between the old plywood and the walls was filled with the same
cement. I asked someone at the local lumber yard about this but he didn't
know what I was talking about - said I should just use some kind of
waterproof caulking around the edges. Good advice?
Any reason for NOT using construction screws instead of nails to hold down
Previous workers didn't think it mattered. No reason to leave more
than a half inch regardless of how complicated the cut is. Google
"tick sticking" - might be one word - for an easy foolproof method for
laying out complicated sheet good cuts.
That sounds to me like the remnants of the last incarnation of the
bathroom. It's possibly the remains of the mud job floor, or floor
patching compound (in this case, mortar) to level the floor for
whatever was the original floor covering (linoleum? depends on the
age of the house). No need to replace it - the new plywood subfloor
will bridge any little gaps.
Not really. If you're going to waterproof a bathroom, that's not the
way to do it. Google Schluter (might have two T's) products if you
will be tiling the bathroom.
Generally I counsel gluing the subfloor with either nails or screws,
but in the case of an older house and a bathroom adhesives are a pain
in the ass to a remodeler. Use screws.
There are a couple of places where the new plywood touches the 1x1 boards
that are at the bottom of the lath & plaster, but mostly 1/16-1/8" gap.
Covered entire bath with one 4x8 - one pc 48x52", another 36x43". Haven't
screwed em down yet, but thinking more trimming is unnecessary.
The floor I pulled looked like 5/8" plywood, linoleum, and vinyl tile. It
looks like a few of the diagonal floor boards were cut out and replaced in
front of the shower, so I suspect none of that was the original floor. I was
intending to lay vinyl tile on the plywood, but now I'm thinking linoleum as
it could all be one piece. There must be some kind of brush-on prep for the
Thanks much for all the information.
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