On 02/05/2021 17:46, newshound wrote:

I was going to suggest something very similar. Another thing you could
consider is to temporarily close off the front and back e.g. by taping
or pinning polyethylene over it, then filling the inside with steam from
a wallpaper stripper for perhaps an hour. That adds heat as well as
damp.


It's plywood - it may delaminate.

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