PR casting question mositure

[Steve54]

While not a pen I am attempting to cast PR in a 1/4 recess on walnut kiln dried bottle stopper. The issue I am having is a frosted look on the bottom side of the cast. After cutting the resin plug from the project to find that it was tacky as well as tacky on the top side. The plug was solid.
I have cast several pen blanks and not had this issue. Is this a possible moisture issue coming from the wood? I attempted this on several different pieces of wood.
Also have sealed the wood with CA and shellac with no change.

Would appreciate any help.

 

[Sylvanite]

It takes quite a bit of moisture to affect polyester resin (unlike urethane resin). When water does get into PR, it looks milky.

Polyester resin shrinks when hardening (actually, it expands when it gets warm in the gel state, and shrinks back a little when cooling - the amount of expansion and corresponding shrinkage increases as the curing temperature rises). If it looks "frosted" on the underside, then it's possible that the resin has pulled away from the wood. One cure for this problem is to do multiple small pours instead of a single large one.

Air contact retards the hardening of polyester resin. It's common for the core of the casting to be rock hard while the surface is still tacky. The surface will harden over time, which you can accelerate by warming it. Alternatively, you can add wax (dissolved in styrene) to the resin before casting. The wax will rise to the surface, block the air contact, and cause it to harden. Poly-vinyl-acetate (PVA) sprays are sold to do the same thing. If you do multiple pours, you want to do each subsequent pour while the surface of the previous pour is still tacky. That way, the PR layers will bond chemically into a single crystal. If you wait until the surface has hardened, the layers won't bond chemically.

I hope that helps,
Eric

 

[Steve54]

Thank you I will start this process tomorrow. Would use and still may use easy cast clear resin except for the challenge of polishing. I used this when I had trouble with the PR. I eventually aquire a acceptable shine however not consistenace even though same mix was used to cast 5 stoppers and all on walnut. Again thank you.
Steve