Thread: home build - mast and gaff - questions

First off, don't thin the epoxy. In fact, you shouldn't ever need to thin epoxy. If you want to lower the viscosity then warm the work and/or epoxy. Thinning epoxy just dilutes it and just a small amount of dilution will make a huge difference in the strength and physical properties of the cured goo. So, unless you have a strong chemical understanding of what happens with specific dilutants, then don't even think about.

The epoxy steps on a birdsmouth mast are; coat all the internal areas of the mast with three coats of straight epoxy (no thinning, no fillers), using the wet on green technique (wait until the previous coat is just barely tacky before the next). Once three coats of neat epoxy are on and it's at the "green" stage, apply thickened epoxy to the notches that will receive it's neighboring stave. Align and clamp (not too much pressure, just enough to insure adhesive contact only). I use plastic wrap, strips of rubber, bits of line, what ever is handy. Once the inside has cured, remove the clamps and begin whittling it down to a round spar. When it's round, fill any gaps in the staves with thickened epoxy. Lastly apply 3 straight epoxy coats to the exterior of the mast.

3 coats seems excessive, but it insures two basic fundamentals, the first is that it has sufficient film thickness to prevent moisture from getting to the wood and second that this hard, plastic resin has encapsulated every square inch of surface, inside and out. This makes it no long a breathing piece of wood, but a dimensionally stable bunch of wood with a hard plastic shell.

As far as a fillet reserve area, forget about it. You're making more work for yourself. Unless this is a very dainty racing mast, who's life expectancy may only be a few races and the strength edge, verses light weight is a very carefully strung tight rope, then it's not worth bothering with. I've made mast that had 15% and less wall thicknesses. They didn't last long, but they won races because they were a few percent lighter then the competition.