Mold sealing

[Agewon]

I have searched through the threads to find a post relating to sealing a mold. I have made a melamine particle board mold (plug) and have routed the edges to radius them, exposing the particle board. How do I seal these edges? Should i apply a light sealer of epoxy then wax as usual or is there another method that is easier?

[alan white]

Several coats of epoxy should be applied, until the radius is perfectly smooth.
You should sand the finished surface through the grits to 1500 grit, and even polish the surfaces to a high gloss. Fill any pits, however small.

Alan

[Agewon]

Thanks Alan. Do you think there will be a problem with the wax and PVA reacting to the cured epoxy? I plant to substitute gelcoat finish of the final part with a coat or two of epoxy.

[alan white]

The layup should be fully cured and the surface scrubbed with a dewaxer and then sanded first. The bond is mechanical, so sanding with 60-80 grit will give the epoxy a good bite. Don't sand without first scrubbing the wax out, or you could drive it into the surface when you sand.
Others who are experienced in epoxying polyester may weigh in on this advice, specifically how much cure time is enough before adding the epoxy sealer coats.

Alan

[waikikin]

Agewon, I do some molding using melamine faced particle board & usually for external corners use a roundover bit but set it a little deep to give a step(for filling) then hotcoat exposed particles with polyester resin & then fill over with panelbeaters glazing putty(like bog/bondo?/jetflex only nicer), you can then re router or just sand the radius in, for internal corners a fillet stick or coin tools off the same putty or plasticine/modeling clay(from f-glas supplier), a heat gun helps application & tooling of the clay, then just wax & spray pva realease agent, if you spray the pva in three passes it should end up sealing the wax pretty good & you wont have much wax if any on the part, melamine sheet usually releases with out wax or pva but its not worth the risk of a stickup Regards from jeff

[Agewon]

Thanks a ton guys. The mold has been built, the edges sealed and inside corners fillet(d). I am going to build up one more coat of epoxy then sand through 1500 before waxing. I did notice that when i was making my fillets with 407 filler, they sagged a bit, but a light touch with a heat gun stopped that.
waikikin, do you buy melamine stock and cut to mold, or do you make the mold and then glue on the melamine and trim? Also, your idea for cutting the radius deep , filling and re-cutting is great. I will have to try that.

[waikikin]

Agewon, I just buy partile board or MDF board prefaced with melamine finish, the more you pay the shinier you get, basically the same stuff kitchen cabinets are made of. comes in sizes up to 12' x 6' here in Aus but the big sheets are tough to handle & not the shiniest ones available. On big tempory molds I'll frame with 4x2 or 3x2 & fix with grabber screws, On small stuff sometimes just a bit of hot melt glue & modeling clay will be ok for like a dash panel insert or such. All the best from Jeff.