On Thu, 23 Nov 2017 10:15:13 +0000
(Roger Hayter) wrote:

Steve wrote:

On Wed, 22 Nov 2017 22:44:43 +0000
(Roger Hayter) wrote:

I have fitted a 150 x 20mm piece of engineered oak plank
vertically behind a worktop. (The long axis of 800mm is
horizontal.) It is fixed well along the worktop but cannot
easily be fixed to the non-flat, non-vertical wall behind it. I
therefore thought it would be a good idea to put some plaster
behind it, both for neatness (a difficult gap to keep clean) and
for support. I used one coat plaster up to 4/5 of the top of the
wooden upstand. Much to my shock, by the next day it had warped
6mm out of the vertical, and away from the wall at the top. The
bottom is firmly clamped. At first I thought it was a mechanical
effect of the weight of plaster (though on reflection this should
not be enough to bend it) but on closer inspection the top of the
plaster is now 5mm away from the wood. There is some evidence
of longitudinal warping, although it only amounts to 1mm in 800
mm, because it is pretty well clamped against the worktop.


So clearly the side of the engineered wood blocks in contact with
the plaster has expanded very significantly. Is this a known
effect of plaster? Would waterproofing the wood first have
prevented it? Will it un-warp in time and is there any way I can
encourage it to?

Many thanks for any comments.



If you're going to have another go at it use car body filler
instead of plaster. Or fill the bulk of the gap with expanding foam
and leave just the last few mm to be filled with plaster to
minimise the wetting.

Thanks for the useful advice, and to everyone else who has confirmed
my error. I just didn't realise the wood would absorb water so
fast.

I am definitely not going to do it again, but will try to remember to
report back in a few weeks if there has been any improvement.


Did the plaster sink and so fill the void left by the timber warping?

If so, I can't see how it could dry back to straight.

If you wrapped the timber in clingfilm would it be possible to remove
it after the plaster set?

Else, shrug; say it's rustic shabby chic.