Thanks Don for the gel coat explaination--I might also mention that after I get to 220 sand paper it is always sanded wet, and with a backing block of some type (with a few minor exceptions).
Epoxy resin--there are a number of different brands, and many different subtypes of resin. I have become used to using West systems--you mix catalyst and resin by volume ratio--there are pumps which fit in the cans and give the proper ratio. (from 3:1 to 5:1 depending on the specific catalyst) With polyester (gel coat)--if the MEK is increased the reaction occurs more rapidly--but too much will result in a poor result. I usually use "slow"--occasionally use "very slow" or "fast" catalysts depending on what I am doing. In the colder climates or winter, I use "fast".
Fillet: One uses filler material to give a smooth radius and avoid a sharp corner when applying fiberglass cloth or materials. Glass fibers loose strenght when bent at a sharp angle, so one tends to increase the radius of any right angle. Basically I use " Cabosil" (Silica powder or fumed silica, a thickening agent) and one of the filler materials (such as micro balloons --tiny spheres, or microlight--a fairly soft filler material). When I was building boats, Bondo worked fine on the inside, but I don't like it on the outside). When you put in the fillet, it is rounded on the inside (I use a tongue plade or special paddle which is sold by "West systems" to make a smooth concave surface).
Glass: Mat is random oriented fibers, which are held together with a seizing compound. Be sure the seizing compound is compatable with the resin you are using (Epoxy or Polyester). Generally mat is available in 3/4 oz, 1.5 oz and 2 oz. It is usually used with polyester, but can be used in combination with epoxy. Mat is cheap but not structurally as strong as other cloths. It is used to fill between layers of other fiberglass materials.
Cloth: from 1/2 oz to 40 oz weights--both in E glass and S glass. S glass is both stiffer and stronger than E glass. There are different weaves. Cloth is one of the basics of thin laminates. With polyester, alternate layers of cloth and mat are used to give thickness and stiffness.
Woven roving is bundles of fibers at right angles and comes usually in 18 oz (I have also seen 24 oz--and there may be others). It gives very good structural strength and is a stable of most of our hulls. Layers of roving and mat. Again I prefer polyester with roving--Epoxy is sometimes hard to saturate,
Biaxial cloth: usually comes with 3/4 oz mat backing, and 2 glass layers at 45 degrees with stitching to hold the bundles in place. Generally this comes in 12 oz and 18 oz, and works well with both epoxy and polyester.
Beads: Usually used for non skid--added to resin or paints--very small glass beads, and rolled on--there are a few guns which will shoot beads, but most folks roll them on. Also they can be sprinkled into wet resin.
I like these better than sand, because they are less abrasive. We used sand on one deck years ago, and in the first 24 hours of a 15 day race I had worn thru the seat of my new foul weather gear, scooting back and forth on the cockpit side decks--mostly steering or trimming sails.
Fillers: Micro fibers--very very fine fiberlass fibers. Milll fibers--courser fibers. Random strands:--I pick apart cloth, roving or biaxial to get bundles of fiber to lay in an opening..
http://www.epoxyproducts.com/2_fillers.html There are some photos of fillers, and some links--I didn't read them, but from the filler page, it looks fairly good--may have time to comment on it later.
http://www.jamestowndistributors.com/us ... &catId=210 Has a good list and short summary of the various fillers--if you want more information, Google each of the fillers.
What project do you want to do? This will determine what you will buy. I would start with a quart of West Systems 105 epoxy and 7 oz of 206 hardner (slow) with a set of pumps). A square yard or several feet of 2" fiber glass cloth--6 oz. Alternatively buy a quart of polyester resin--it should come with MEK. I would buy some Cabosil, medium density filler, get a bundle of popcicle sticks at a hobby store, use yogart containers for mixing (or small metal cans). See pages 323 thru 329 of West Marine Catalogue for various materials. I would also buy the West Systems book on epoxy, and do some googling on the internet on both epoxy and fiberglass repairs:
http://www.fibreglast.com/contentpages- ... fiberglass
Has some good basic information
I am sure that others will jump in with good sites. I put up a number of photos, then pull some of them down--because I don't think they are of general interest. Fortunately I don't have another project right now, or I would take more photos. But a little searching on the internet will find the techniques. Some of the repairs and modification is fly by the seat of the pants. Fiberglass is very strong, vesitile and very easy to work with.
Hope this helps some.
