[VAC] OSB Floor?/floor patching

["Robert / Susan Harper" <rharper@xxxxxxxxxx>]

Jim, I had just a couple of small (about 3 sq. ft.) spots to patch, and I
used standard 3/4" AC (maybe it was BC)exterior plywood, but I had to reduce
the thickness slightly where it laid on frame and cross member parts to make
it flush on top. I did not go for a perfect fit, but left about 1/16" gap
around the edges between patch and orig. floor. After bolting the patch to
frame, I shot expanding foam (Great Stuff) into the gaps I'd left. When it
set, I flushed it up top and bottom, then installed a bridging patch (strips
of same plywood) on the bottom side of the plywood floor (belly pan off).
The patch had to be reduced in thickness where the bridging patch laid also
(easy if you have a table saw).  The bridging patch was installed with
polyurethane glue (one part, I used Franklin) and lots of screws.  Then I
painted everything from the bottom with enamel primer.
Water hurts plywood the fastest by getting in at the edges. The cell
structure of the wood is such that it is drawn in like a straw on the "end
grain", which is exposed on every other layer on plywood edges.
Even if you patch with OSB or marine plywood, it wouldn't hurt to take
precautions to seal edges. Sealing the faces is good, too. OSB is good
stuff, because of the "O" part - oriented. That means they line up the chips
in a linear fashion in the sheets to give you that same type of strength you
get in solid lumber.  But you'd be wise to further protect it from moisture,
since any leaks could go undetected for quite a while.


Bob Harper
'62 Globe Trotter in SC