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> One of the nice things (?) about polyester is that you use one hardener,
> and you can adjust the amount to match your working temperature. That is
> also one of the problems: First you have to know the temperature before
> you mix anything. I have no idea why it turned dark, though. That doesn't
> sound right.
Paul,
Polyester uses keytone peroxide as a hardener, in liquid form. The trouble is with the mixing ratios. The ratio is 10-12 drops for every ounce of hardener. Now this doesn't sound like a hard thing to accomplish until you mix up a quart which is 32 ounces. Now you have to count to 320-384, which is tough when I have both of my shoes on. {:o)
The drops ratio (it is written this way on the label) works out to about 2%. This is where the problem of darkening comes from. Most people think that if a little is good a little more is better, but in this case a very little bit more is way too much. Warm temperatures use 10 drops cold use 12 drops. You have to figure out where the change happens and how much to compensate.
This whole thing is a hit and miss proposition, and takes a fair amount of practice.
By the way the new Corvettes (since about 1986) use Sheet Molded Compound (SMC) which is glass fibers in epoxy resin. The SMC part is made by putting a lump of SMC into a press, form it to shape and then heat it to about 200F to cure it. This gives the part a paintable surface on all sides. Now if we could figure out a way to use this process to make a beautiful wooden kayak, we could make some coin!!! {:o)
Ian
This is an archived message from The Kayak Building Bulletin Board.
Guillemot Kayak - High
Performance Wooden Sea Kayak Designs
