: Thanks for all the advice guys. I think for me; being brand new to
: this, I'd feel more comfortable going the seal coat route. I am
: also using multiple wood species, so Bill's point about
: different absorbtion rates would apply. Here's my next
: question.... I'm using MAS epoxy with slow hardner and was
: watching some of their demonstration videos yesterday. They
: suggest that when using the Q-tip method, once the resin is no
: longer tacky (won't pull Q-tip fibers) that you need to sand
: before subsequent coats.

Kinda true. They simplified it. Here is a longer version of the story. Your epoxy is made up of a resin and a hardener. When these two chemicals mix an exothermic (heat-producing) reaction occurs as solid strings of plastic molecules link up, pulling their components from the original liquids. The process is called polymerization. After a short period of time there is a "framework" of sorts of these interlocking strings of plastic polymers. They are long, interlocking molecular chains. As these chains grow longer, and tighter together, they bind up any remaining liquid. As they do, the material thickens and gels, and gets warm. Heat accelerates the process, and it produces some heat as it polymerizes, so things speed up once a critical volume of resin is mixed, or a certain temperature is reached.

The expanding mass of linked polymers is like a sponge, but as the polymer chains grow, they squeeze out of that "sponge" any chemicals that don't fit into their molecular formula. This could be small amounts of excess resin or hardener, or some materials which were put in to stabilize the chemicals, make them mix easier, absorb UV, waxes for mold release, and byproducts of the reaction, or waste components. Since there is not a lot of iner-molecular space to keep these things on the solidifying interior of the mass of resin, a lot gets forced to the surface. Imagine a sponge squeezing itself dry, by pushing out all the water it had absorbed.

Once the resin has gelled, it will become tack free, but still be flexible. This is the "green" stage when it is easy to trim. The polymerization process has slowed down, but it has not yet stopped. It may take weeks at room temperature for the resin to completely cure. Some people will bake their boats at 120 degrees F for a few hours, or leave them in the hot sun for a day or two, to add heat which will speed up the final curing process and harden and strengthen the epoxy. For critical applications, such as using fiberglass parts on airplanes there are special times and temperatures for heat treating the resin, but we usually don't bother. Once the resin is completely cured it is inert, and in most cases it is even FDA approved for contact with food. (There is some question about the food safety aspect of the Bisphenol-A in the epoxy, but that is an unresolved issue right now.) Until it is fuly cured you can become sensitized to it and get an allergic reaction. So watch the dust.

The waste products end up being glued to the top surface of the resin, where they form a thin skin, which is not as strong as the underlying resin, and it is like a coat of wax --it keeps the next layer of resin from getting a tight bond to something stronger. So, if you wait until this upper surface is hard, then the clear waste on the surface has to be removed before you put on another coat of resin. Using a cotton swab to see if the surface has lost its tack is one way to determine that the reaction is pretty much over, and the surface is covered with clear waste. Since many epoxys produce a reaction that produces excess amine compounds, and since these amine compounds are a good proportion of what gets pushed out of the epoxy, the junk on the surface is frequently called "amine blush" If the amine layer is thick enough it isn't clear, and the light tint that it has is the source of the "blush" part of the name. The amine component will wash away with a rinse of very hot soapy water, or a weak ammonia/water mix (add some soap if you wish). So you have a third option here. wait until the coating is hard and just wash it. Much safer and no tools other than some rags and a washbucket.

After you sand, wash, or scrape the surface you have a solid, hard base which your epoxy is very happy to glue to. And epoxy is a VERY strong glue, with a bond of maybe 2000 pounds per square inch (probably a lot more). So when you have a strip of glass cloth glued to two pieces of wood each 3/4 inches wide, and 10 inches long, the strength on that area is some 30,000 pounds. It is going to be pretty darn hard to tear those strips apart! The resin which saturates the glass traps the woven fibers and bonds to them, using that matrix to transfer forces. Any coat of resin you put on top of this is just for the purpose of filling in the pattern of raised and depressed areas left from the weaving of the cloth fibers. In effect, the second and third coats of epoxy are a thick, clear, expensive and very tough, very water-resistant paint. If this "paint" barely stuck to the underlying first coat, it might chip off, or delaminate over time. But that would not significantly affect the strength of the boat.

If you want to avoid sanding, you should work faster. If you apply another coat of fresh epoxy on top of a layer which has jelled, but is not yet hard, then the growing chains of polymers in the fresh coat will start stealing available chemical components from the first layer. Those new chains of molecules then become intertwined with the mass from the first coat. When it all hardens it is essentially one solid piece.

: I really don't want to mess this up, so
: I'd appreciate if anyone has any experience with MAS epoxy and
: applying glass after the tack has left. I sure like the sounds
: of this method, but I want to be sure it will work.

If you can afford the time, wait a week or two after the tack is gone before you sand. The material you remove will be harder, less likely to gum up the sandpaper, and less chemically reactive. Wear a respirator when sanding epoxy, particularly fresh epoxy. Breathing in the dust might eventually sensitize you and make you allergic to epoxy. Then you have to give up the hobby, or be VERY well protected. If you are in a hurry, don't sand. You can use a scraper on resin which is still tacky if it is stiff enough to work on. You just need to keep wiping the goop off the scraper. Or, wait and wash.

: Also....before I took the deck off the forms, I seal coated them
: with the MAS epoxy using a foam brush. It seemed like it worked
: OK, but after it has hardened, it's splotchy looking. I'm
: guessing some areas saturated with wood, and others were still
: drinking when the epoxy kicked. I don't think this should be a
: problem and will disappear when I get around to glass the deck
: right?......

Yup, you got it. Problem with sealcoating with a brush is that you put on too much resin, and you didn't come back with a stiff squeegee and scrape off the excess. I bet you brushed back and forth to make sure the whole area was well covered, too. That just added more resin to areas that already had some. Use half, or even 1/4 of your resin next time, and don't go back over an area you've hit. Mixing the smaller batch will keep it from kicking so soon, spreading it thin will keep it from kicking so soon, and not going back means you'll hit the entire boat with 1 coat in the time it took you to do half the boat with two passes of the brush. Do it Sunday morning, clean up, congratulate yourself on how fast this is going, and go watch a football game.

Where it does not soak in completely it sits on the surface and hardens to a shiny finish. Where it soaks in the finish is very matte. Matte is good. It has a greater surface area for the next coat of resin to bond to.

When you apply your glass be careful to wet it out, and again go over it with a squeegee. You can use a soft squeegee here. Since you sealed the wood any excess resin is going to puddle on flat surfaces, or drip or run on vertical surfaces. So don't leave any excess resin. You want exactly as much as it takes to saturate the cloth and turn it clear. Capillary action in the fibers holds the liquid resin in place until it starts to gel. Liguid which is not trapped in the fibers will spread out or run. You'll need to scrap that or sand it to remove the bump.

Hope this helps.

PGJ