Join Date: Oct 2006
Location: Callao, VA
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Re: plywood type for fiberglass .
you would be better to use a piece of hardwood (oak/hickory/etc) and epoxy coat that....
you can then see what is happening to the wood....
Plywood is going to "squish" over time unless you are using multiply/specialty ply...
the home stores carry 4,5, or 7 layer, up to 3/4"....but that is poor for your purpose from the get go.