I have a joist that bows upward, causing my plywood subfloor to be
uneven (3/4" over 4ft). How do I level the plywood subfloor in order to
install nail-down 3/4" wood flooring? I thought about using a leveling
compound such as LevelQuik RS, but I was told that the compound will
crack if I try to nail the flooring through it and into the subfloor.
I tried using some roofing shingles that I had in my garage as someone
suggested. When I test fitted the flooring, the 3/4" drop was cured,
but I ended up with a new problem: The flooring was uneven in the other
direction, creating gaps and a buckling effect.
Any other suggestions?
P.S. I don't want to go to the extreme of cutting and sistering the
joist if I can get around it.
Can you turn the joist upside down and then temporarily frame off the
bowed down bit so it's like the walls of a bathtub and fill with some
kind of a liquid filler and allow it to self level in the bowed area.
Then when it's dry remove the temp frame? Just brainstorming. Or grind
down the bow with a heavy grit sander, or plane the bow with a wood
Don't try to level the floor.
Try to minimize the out of level condition. 3/4" in 4ft is noticable, but
3/4" or 1/2" over 10-12 feet probably isn't noticable to most people.
Instead of using roofing shingles, use #30 and/or #15 building paper. You
can then layer the building paper so that the bow gradually transitions into
the rest of the floor. You'll probably need to use a string line to create
your taper, and then build up with paper to the string.
Any other suggestions?
Cut the offending joist completely in half at it's highest point and slide
in another STRAIGHT joist next to it.
Nail the two together, flush at the top.
You might need to pull the crowned joist down to make it flush with the
It's a ten minute job.
Don't make it an all day affair.
Having just done this to the whole second floor of my house, if it's only
one joist you will spend more time screwing around with shingles and
leveling compound that just pulling up the plywood and fixing the joist.
Pull out the plywood nails with a nail puller. Correctly done it should be
a gouge the size of a dime.
Buy or make a very straight board. Clamp the board to the side of the
problem joist down far enough to use it as a guide for your circular saw.
Run the circular saw down the length of the crowned joist and cut the 3/4"
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