Hey if the thread is awake I might as well add a comment. This idea comes from another project but might be good for sealing spoil boards. I used a few weeks ago the "epoxy" resin used for counter tops and bar tops. Basically a real thin self leveling material. The interesting thing this was on mahogany and let me tell you that stuff soaked right in. The mahogany wicked it right up.

This particular material tacks like 7 hours just to tack up and 72 hours to harden. However after watching it soak into wood and the very slow set up times I'd have to think it would be a good sealing and hardening solution for porous sheet goods.