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

Is this a known effect of
plaster?

Of the water, yes...

Would waterproofing the wood first have prevented it?

Probably.

Will it un-warp in time

probalby....

and is there any way I can encourage it to?

You could wet the front, which would cause it to warp the other way.

Best to very firmly do nothing for a few weeks, though, and then see.


Thomas Prufer