Is it possible to plaster directly onto vertical plywood, maybe after
treating with PVA? I've got a rather tricky RSJ to box in the new bathroom
and it's a tricky position to fix studding for plasterboard.
Further investigation with bits of framing shows that thinner plywood
wouldn't help either - there is no obvious way to get around the RSJ with a
frame and plywood or plasterboard on top. However, I have another cunning
plan... Assuming that you can tile onto plywood, I assume it would be okay
to tile over a 1" bit of wood? What I'll have to do is construct a frame
which comes out flush to the wall level but then build another smaller frame
inside, set back the width of the plasterboard into which a piece of
plasterboard can be fitted.
How come it's always the bits you forget about that take most time!!
Assuming you mean "Is it possible to _tile_ directly...", the answer is
yes. In fact, I'm doing just that as we speak - our ensuite is entirely
3/4" WBP, PVAed, and I'm tiling the whole thing floor to ceiling.
I believe that skimmed plasterboard gives 1/2 hr fire resistance which is
probably the minimum for load bearing RSJs, plywood is not a substitute.
Suggest you speak with your local building control office, they will advise you
with the required fire protection. Do not rely on comments made by enthusiasts
on this NG, however well meaning they may steer you into making a colossal CU,
go to the above mentioned office.
How do you mean "far wider" ? If the RSJ is on the outer leaf and the inner
leaf of the wall is dry lining, then it should be possible to fix a batten
to the bottom part of the RSJ and batten across the studs of the dry lining.
Once you get these battens in place the boxing in should be a doddle.
If you can get a fixing for plywood on it, then why can't you get a fixing
for plasterboard on it ? The best and strongest way is to drill two or
three holes through RSJ and screw through on to battens of timber. Or
simpler is to cut lengths of 2'' X 2'' just longer than the gap between the
top and bottom leaves and hammer them in at a slight angle until they grip
fast. These end up just like timber studs and you can fix anything you want
to them if they're tight enough.
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