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The different resins have different characteristics, and there's plenty of info available on the web about each one. In a nutshell, epoxy is considered the most desirable, because it is strong, bonds to anything, and has good "secondary bonding" characteristics (when you're bonding to cured resin). Polyester is cheaper, not as strong, and doesn't bond particularly well to wood or cured epoxy resin. Vinylester is rapidly becoming my favorite resin. It is as strong as the best epoxies, and its mechanical properties (shear strength, modulus, etc.) exceed those of most epoxies. It has very low viscosity, which makes it easy to wet out fabrics, and the ratio of resin to accelerant is highly variable, meaning you can use it in many conditions. (Even though I've used many epoxy resins, Dow Derakane is the only vinylester I've used, so I don't know if all this holds true for others). The biggest drawback to vinylester is that, like polyester, it contains a lot of styrene, which stinks and probably causes brain damage. I use epoxy in my workshop with just a fan on, but I use my organic respirator every time I touch the vinylester. The esters are "air inhibited." This means the surface will not cure if it's exposed to air. This is great for secondary bonding, since it means you're really laminating the two pieces together instead of just gluing one part onto another already cured part, but it has some interesting implications for sanding and fairing. The esters come in two types: waxed and unwaxed. The unwaxed resins are for laminating, because another layer can be applied on top of the first without any surface preparation other than cleaning. The waxed resins are for the final coat. As they cure, the wax "floats" to the top, blocking air and allowing the surface to cure. After cure, you wash the wax off with a solvent and you can sand the surface. If you don't use a waxed resin, or if you don't wash the wax off, it takes about 9 seconds to completely ruin an expensive resin fiber sanding disk by gumming it up with uncured resin. I feel that your biggest criteria when selecting a resin should be viscosity and then price. Viscosity first because thick viscous resins are very difficult to work with. You will end up using a lot more (maybe twice as much) trying to get your fabric thoroughly wetted out, so any money you saved by buying a cheap resin is lost. You will also be very frustrated by your lack of progress. USCI is my default choice for a general-purpose laminating, but their fast hardener is much more viscous than their slow hardener. Unfortunately, you really want the opposite, because when ambient temperatures are too low to use a slow hardener, your resin is also likely to be more viscous. So in wintertime I use WEST System and in summer I use USCI. In winter, I also store my resin in a small styrofoam ice chest with a 10-watt lightbulb, which keeps it nice and warm. Make sure you line the bottom of the ice chest with plastic because the hardener is caustic and will eat through the stryofoam. I still recommend buying gallon samples of many different resins and figuring out what works for you. If you really don't like a resin's properties (too viscous, cures too fast, cures too slow...) you can always use it up in small batches for filleting and fairing. I'm using all these different resins, but not by choice. When I started building my boat, I made many parts from vacuum-bagged epoxy. Then I bought hulls that were nearly complete. The builder had gotten an epoxy allergy during construction of his last Farrier trimaran, so he built his hulls from Derakane. There are significant variations in price for resin, but I have not found significant variations in mechanical properties. In other words, most epoxy resins are well within the range needed for building boat parts. The differences in mechanical properties may be important for 90-foot carbon fiber wind turbine blades but not for boats. The range of flexural strength for the epoxies I considered was 11810 psi for standard WEST System to 19077 psi for WEST's Pro-Set laminating resin. Most of the rest are within this range, but Dow Derakane has a flexural strength of 22000 psi. If you consider that standard WEST resin is about $70 per gallon (2007) and specialty resins can hit $114 per gallon, the $47 per gallon price of Derakane starts to make all that styrene a little less noxious. One cardinal rule of mixing resins is that poly/vinylester will not bond to epoxy. Likewise, epoxy will not bond to uncured or unwaxed poly/vinylester. Since my hulls were vinylester and my parts epoxy, I had a problem. The solution was to coat all areas of the hull that I was bonding to with a waxed polyester resin: good old Bondo, from the hardware store. At $15 a gallon, it's the cheapest resin I've ever bought. Since almost all of it was going to be sanded off anyway, its mechanical properties were unimportant. (I'm not talking about the auto body filler. That stuff is made with silica, and is incredibly heavy and hard to sand. Bondo also makes a fine resin for household gluing). I've divided the boat into two zones: "epoxy-tainted" and "ester". And epoxy-tainted zone is any place where I've bonded in an epoxy part, or otherwise laminated with epoxy. I can't use any type of ester resin in these areas, because it won't bond. An "ester" zone is an area that has never been touched with epoxy. In these areas, I can continue to use vinylester resin for laminating and taping, and polyester resin for filleting and fairing. At this point, the only 2 areas that have never been touched with epoxy are the stem and the v-berth. If I had to start from scratch, I would start with Derakane. It's only big drawback is the styrene: it stinks and it's really bad for you. But I wear an organic respirator any time I'm fiberglassing with it, and so far have had no problems. |