[VAC] Expanding foam/water leaks/ply floor edges/bellypan/world peace

["Robert / Susan Harper" <rharper@camden.net>]

Thanks for input, Scott.

***WARNING**** This is lengthy, and for most people, quite dull! If it's not
interesting yet, delete and move on .... while you still can!

I will not be filling the wall cavities or the belly pan with foam, just
"caulking" the gaps between the edge of the belly pan and the plywood floor
with the polyurethane foam (from BELOW - my belly pan is off except for
about 8" of the original I left around the perimeter, and it is hanging
nearly straight down in most places). The spaces I'm hoping to seal with the
polyurethane foam are 1/16 to 1/4 inch wide, and 3/4 to 2 inches high
(plywood plus aluminum u-channel used as lower plate). The belly pan edges
come up inside the walls above the top of the u-channel.

I disagree re: floor rotting being caused by water collecting in the belly
pan. I think it's the water that CAN'T get into the belly pan that causes
the problem, meaning it sits on top of the floor or goes into the edges of
the plywood. Most belly pans are no where near tight enough to hold water,
at least not so much water that it would reach the floor. I'm planning on
providing a few small drain holes (screened for insects) in the low points
of my new belly pan. I expect to offset the pan from the frame with strips
of rubber about 1/8" thick, leaving occasional gaps to allow water to flow
to a few drain (low) areas.

I make my living building furniture, and was formerly in construction, and
in my experience, the main problem with water on plywood is getting edges
wet (or CONTINUAL wetness on the surface). The foam from the bottom is
intended to seal the plywood edges. This would stop water above floor level
if I have a leak in the skin somewhere. Not good. I hadn't really considered
that possibility.
Polyurethane foam does not absorb water. So water in the walls would sit in
the u-channel (lower plate for wall construction, bolted and screwed to
plywood floor) or around it, including on top of the plywood floor. It would
also seep into the core of the ply floor around the fasteners.

My primary areas of concern are the rear corners of the trailer, where I had
damage before. Although I believe the previous problems were caused by the
dead water heater (leaked) and the tub/shower (ditto), I also had loose
areas between pan/skin/floor all the way across the back edge of the
trailer, the lower plate having crumbled from stress after being weakend by
corrosion caused by the leaks. Those problems have been repaired, stronger
than original, and I think since I still have interior skin off in those
areas, I will also caulk (vulkem or rubber caulk) between skin and
u-channel, spot-foam at the ends of the u-channel, spot-foam over all
hardware holding the u-channel to the floor, and caulk on the inside between
the u-channel and the ply floor, as well as between the inner skin and the
u-channel when re-riveting. (All of those steps done from the inside of the
trailer.)  Now any interior water (between skins) in those areas would be
held in the u-channel. This sounds like a lot of trouble, but really is only
about an hour of work at the current level of disassembly and for the small
areas I'm discussing. So the remaining concern would be knowing that there
was water collecting in the u-channel or running out onto the top of the
plywood floor. Both of these areas are likely to be hidden by shower pan,
bed, or cabinetry, meaning difficult to check on them. I could imagine
"interior-plexiglass-u-channel-viewing-portals" or a system of
"miniature-u-channel water level monitors" , but this is starting to
get obsessive (probably passed that point for most of you several messages
back).  Maybe a small drain tube in each corner would be enough, leading
down to (or through) the belly pan. Yes, they will probably get clogged up,
just like the weep holes in the bottoms of car doors.

After all of this thought and imagined future troubles and damage, I am
reminded that the trailer lasted 38 years (so far) without any of these
measures, and another 38 years will put me at 83. Then the next owner could
do again all that I've done so far.

Any input (if anyone's still there) appreciated. If you're shaking your head
at this point, what can I say. I warned you.

Bob Harper
'62 Globetrotter in SC