Polyester questions:

[philcanoe]

I am currently building a traditional wood strip canoe to be used as an plug, for a female mould(mold?) My question is concerning using polyester 'laminating' resin and sanding. I have always used epoxy in the past, but in an effort to cut cost I'm debating the use of a polyester laminating resin. Normally I would epoxy and paddle till satisfied, but this is the third take and only minor cosmetic changes where made from the last time.

I ran into a problem with uncured resin, and had to PVA over hull to enable
a full hard cure. This was when using the laminating polyester thickened with Cab-o-sil as a body type filler (for fairing). I was told subsequently that a melted parafin wax, could be added to cause an air inhibited polyester resin to cure.

My question(s) is (finally) will this be as hard to sand (due to wax build up), as a sandable-gray type product? And at what rate should the parafin wax be added? Also are there any tricks to remove the wax build, short of acetone?

[yokebutt]

Phil,
The best way to seal the surface for full cure is to spray on PVA. It dissolves with water, then you just give it a light sanding to remove the last of the contamination, with wax you should really do two passes with wax remover (not acetone) before sanding to make sure the sanding doesn't just smear the wax around.

Sanding-wise, it shouldn't be that much harder to abrade, that's mostly a function of what type of filler you mix it with, I like mixing 50/50 gel and VE resin, and then add enough Q-cell to make a putty, for vertical applications I add some silica.

Biggest issue with polyester is that the bonding-strength is only around 1/10 of epoxy, but for a plug it should work alright, look into the Duratec primers, they're easily sanded, and will take polish well enough to build a mold on.

[philcanoe]

Thanks Yokebutt,

I had a problem with the PVA over a really thin buildup of polyester/cab-o-sil; but it's my belief that with additional laminate thickness that should not be a problem. Also probably should have increased then ratio of MEKP, after talking to a buddy.

I was never properly introduced to the world of polyester resin, starting with
vinylester and quickly going on to epoxies. None of my boat (canoe/kayak) building buddies had either, as polyester doesn't hold up well to rocks. My experience with polyester ran out with tooling gel, gel coats, sytrene, and laminating resin only to build up mold thickness.

Many thanks again!