PLEASE HELP - Weather Proofing Hardboard?

Hi-
I need to weatherproof some hardboard so it will withstand being outside for at least 12 months.
The board will be mounted on a panel of another type of wood that will not warp, I plan to glue it on with Liquid Nails.
What is the best solution for protecting it? I thought to use some exterior wood varnish on the front, back and edges. Will that be sufficient?
Thanks
Joel
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wrote:

Replacing it with foamed UPVC. You haven't much chance of weatherproofing hardboard, outside Arizona. If you're desperate for wood, then use a waterproof plywood instead.
-- Smert' spamionam
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