So we use MDF extensively to build cheap, accurate, male molds. Up until now the shapes have been simple enough that draping a release ply could act as our finish surface. Now we want to start molding directly off the surface for more complex shapes. The obvious option is to spray a gelcoat surface (perhaps a layer of glass to seal the surface first). I have two problems with this: first, it changes the surface dimensions slightly and second, I hate spraying. So my next idea was to brush on the gelcoat (smooth-on’s new epoxy gelcoat?), but this only fixes one of the two problems. So here is my proposed solution: seal the MDF with a light elmers/spirits mix and then wax it real good. Anyone ever try this with luck? Our temps dont get above 180F, so MDF has always performed fine for us. I could really use some fresh insight on this one…thanks.
I’ve used a paint system on mdf moulds succesfully. First sealed the mould with epoxy, some filler here and there,sand with grid 80, a thick epoxy coating, sand to 300, PU paint system, sand flat, polish, and then I made some products out of it, or when it was a CNC’d plug, pull off a mould.
Seal with polyester/ vynilester resin then spray duratec vynilester white primer. put in in the oven and you can sand it in a couple of hours. The beauty of this product is you can apply it over 80 grit scratches then go through your grades and buff it, its a one step system. job done. Or if the part needs a little fairing use the first hit as Hi-build then just a light couple of passes with a second then wet rub. Brushing anything is going to be a labour intensive effort to get those brush markes out, it’s also a lot harder to get good coverage.
Not sure what elmers/spirits is ut it needs to be a good “Sealed” surface if you want to pull a vacuum. If your not vacuuming I have used Shellac then waxed and had no problems.
We do not pull a vacuum against the mdf, we pull against a lower caul plate. The shellac then wax sounds good and easy.