From: "John Howard"
Sender: Star45@yahoogroups.com
Date: Sat, 27 Jan 2007 17:03:19 -0000
Subject: [Star45] Re: Epoxy resins and hardeners for glassing hulls
Dave, Sticker shock, ouch? West Systems Epoxy is expensive but good stuff. The quart size will work for several hulls, so buy only what you need, it has a fairly long shelf life if store properly ( a couple of years, not 20). Check the West Systems web page under product info http://www.westsystem.com/ . Lots of good info, but a lot of reading also. The nice thing about epoxy is the low or nearly non-existant oder. The bad thing, some people can be come sensitized to it so wearing gloves, a mask (organic vapor type), a long sleeve shirt, etc. is recommended. More info on the web site. The fiberglass, 9 oz., seems heavy IMHO, 2 layers may be overkill and give you a floating tank. Are you planning on running over the competition and win by atrition? :) That's if you can catch the lighter boats.
I would use a max of 6 oz. cloth. Check and see what others say. Suggest you start with 2 oz. for the first batch and adjust as you go, you will soon figure out how much you need for the hull and the weight of the glass you are using. Get and use the pumps, it makes measuring out the correct ratio so much easier. West Systems, using the 105 Resin with either 205 Fast Hardener (9-12 min working) or 206 Slow Hardener (20-25 min working) will give you enough time to mix additional resin if needed. As long as the additional resin is applied to the first batch while still green (soft) there will be no problem as the new batch will still chemically bond with the previous batch. Once the resin has hardened completly, it will need to be sanded to provide a surface that will mechanically bond to the next resin coat. Cedar Strip Canoe builders do it (mix additional resin) all the time when they fiberglass a hull. Pot life for mixed epoxy can be extended slightly by pouring it into a shallow container (pie pan). Left in a mixing cup, the heat generated by the chemical reaction during curing will set up faster and unused (left over) epoxy can get hot enough to melt a plastic container/cup. Recomend not to use alcohol for thinning, it will change the chemical properties of the epoxy, weakening its strength and water resistance and if too much is used, may not set up.
If you need to thin the epoxy, warm the surface (hull) with a heat gun, this will thin it out and also speed up (lessen the working time) the curing time. When I fuel proof a model airplane, I put the epoxy on straight and then hit it briefly with the heat gun. You do not need to raise the temperature much. As you apply heat, you will see it thin and spread. When cooled, the epoxy will have all of its original strength and water resistance. Denatured Alcohol has no water in it, unlike your drugstore Isopropyl Alcohol 70%(Rubbing Alcohol) which can have up to 30% water in it. Isopropyl is also available as 90%. Use Denatured Alcohol, Acetone or Lacquer Thinner for clean up and depose of the materials (rags, paper towels, gloves and uncured resins and hardeners) properly. See the West Systems web page for more info under the Tab: Using West Systems Epoxy. There are other epoxy systems out there such a MAS, System 3, RAKA and others, but I do not have experience with these brands, West Systems is as close as my local marine supply store. You might also check some of the model shops for Zap Z-poxy finishing resin, don't know how well it will work or the cost in comparison, but some model airplaners use it. Hope I haven't scared you off from fiberglassing you hull. It is easy and safe IF you follow precautions. Good Luck. John
