On 23/11/17 11:08, Tim Watts wrote:
On 23/11/17 09:13, Martin Brown wrote:
On 23/11/2017 07:40, Tim Watts wrote:
On 23/11/17 00:20, jim wrote:
(Roger Hayter) Wrote in message:

So clearly the side of the engineered wood blocks in contact with the
plaster has expanded very significantly.Â*Â* Is this a known effect of
plaster?Â*Â* 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.

It is the dampness and perhaps to some extent the heat of cure coming
from the plaster and goiing into the wood. Wet wood swells up as it
absorbs moisture - some it it is probably reversible but perhaps not
all. It would have been safer to plaster first and then attach the
wood (or remove the wood plaster and let it dry for a couple of weeks).

Pafge 15 of this has the coefficients for guestimating wood
dimensional stability with changes ambient humidity (US timber).

https://www.fpl.fs.fed.us/documnts/f...tr113/ch12.pdf

Let it dry out before you decide to rip it off. Chances are it
Â* will recover in a few weeks as long as environs are dry &
Â* warm.

Next time (if any) use an adhesive & deal with gaps etc afterwards?

Engineered might. Solid oak won't.

Seasoned solid oak won't but green worked oak will change dimensions a
bit as it dries - especially if as is common it is used as a mantle
piece above a wood burning stove where it gets nice and warm.
Dimensional stability of wood with humidity is interesting.

Oak also has a tendency to cup if it gets wet - my personal experience
(due to wet plaster) was very dry oak - been dried, been machined, been
inside for a while.


sigh. All wood has a tendencey to cup if its cut tangentially to the
tree trunk surface. Only 4 planks will not cup when cut from a
quaetersawn trunk.



The cupping was about 1/8" in 8" - I managed to sand/plane most of it
flat in situ.

But oak is known as being a more of a bugger for wet related
warping/cupping than other species commonly found in a house.

No, it isn't.

In fact wood expansion between humidity or 'wetness' changes is fairly
constant amongst all species.

It's just that you dont normally have pine or other softwoods exposed
where you can look at them. Pine is a complate **** for warping.
largelry because its cut from smaller boles and so teh graon goes in
every which direction across the planks.

And where you are showing oak, you likeley want to see the open grain
patterns, and that means tangential sawn raher than quarter sawn.

Tangential sawn always cups on humidity change (wetness) since shrinkage
from green is alwayts greater tangential to the surface of the wood,
rather than radially towards the heart wood. Thats why sawn logs dry out
with radial cracks


ratio of longitudinal shrinkage (the height of the tree) to radial to
tangential is IIRC about 1:3:10.


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