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How to Apply Polyester Resin

Fellow Polyester Resin Experimenters:

If you're thinking of finishing your epoxy-glassed kayak with polyester resin, I'll pass along how I was told to do it by the folks who do it every day.

Make sure the resin you buy has UV protectant. If you can only get the laminating resin with UV protectant as one poster reported today, you will need to add a wax/styrene mix. It is sold separately by resin suppliers. Laminating resin does not cure hard enough to polish, it is designed to bond properly with additional coats of resin. Clear, or finishing resin contains a wax/styrene mixture that comes to the surface and prevents the air from coming in contact with the surface (similar to the amine blush we see with some epoxies) - This allows the polyester resin to cure very hard, able to be buffed & polished. The resins are otherwise identical except for this addition of wax for the finish coat.

Before you start mixing resin and MEK, you MUST stir the resin/wax mixture thoroughly - the wax tends to separate from the resin, and you must mix it VERY thoroughly before pouring some off. I was told I could not mix it too much 8-)

For a finish coat, you want to mix a "cold" mix, meaning about 0.5% MEK by volume (200:1). You want it to remain thin and not "kick" too early, as it levels like a dream given enough time. No "tipping off" will be required either, as any bubbles you create will rise and pop in short order. This would be about 2cc to 16oz of resin if I did my math properly. I think most resin mfrs recommend a 1% mix ratio, we want to halve that.

Mask the boat into 2 halves, hull & deck. The proper way to apply and get great results will drip, so keep it off the side you are not working on.

Mix about 16oz, pour it down the centerline, spreading it with a brush as you go. You don't want to play with small batches and lots of delicate brushing, as you're bound to get brushmarks and bubbles that won't go away as it thickens. You want to spread it freely all around, letting it flow and self-level (and drip off the sides :-). The brush is there primarily to spread, and make sure the resin is wetting the surface. This reminds me of the way they taught me to glass the hull, which I found to be quick and efficient - albeit with a squeegee instead of a brush.

Unmask while the resin is green. When the coating has cured, wet sand starting with #400 (using a sanding block!) and then up to wherever your buffing method requires (i.e., #1200). Here's my favorite finishing page:

That's it, one coat should do it IF you allowed it to flow out properly. I figure about half will end up on the floor, and you'll sand off a few oz., leaving about 4-6oz per side of the kayak. Not bad for a liquid glass-like finish that will preserve the color of your wood grain . . . I can't tell you how "impressed" I was by the finish on their surfboards.

Hope this helps, Spidey