Epoxy questions

[Johnny Socko]

Well I got her flipped. Time to work on the bottom. My questions are when dealing with wood flour do I epoxy the area first and let that dry or put my flour epoxy mix on with the first coat still wet? Secondly same question with fiberglass.

Thanks,

John

[Ray Frechette Jr]

when taping seams I wet out, filet with wood flour and then lay glass tape and wet out tape before anything has cured.

When laminating wood together,  wet out the wood, both surfaces,  mix in some flour to make thickened epoxy and spread and then clamp and remove any squeezeout.

If glassing hull, I wet out any divots and fill with thickened and let cure and sand and refill and sand as needed.  Once surface fully fair I wet out everything and let cure.  Go over everything with a scraper or sandpaper to take out hangs and then spread cloth and wet out cloth.

[lewisboats]

For my fillets I usually wet the joint first...this keeps the wood from pulling too much epoxy from the filleting mixture. Then I use a nice, thick, almost dry mixture of wood flour and epoxy followed by a strip of glass cloth and then wet the whole thing out and smooth it over. A final coat is put on to fill the weave of the cloth once the tack starts to go away but before it is tack free. I have also done it where the fillet is left to almost cure then the cloth is added...this results in a neater final product as you can use masking tape to make nice straight edged fillets. Doing it this way also saves the sanding needed if you let the fillets cure thoroughly prior to taping. I use the masked type if I am going to leave the filleted area bright or there is a reason to spend the extra time to make them pretty.

For glassing...it depends on if you are glassing a dry laid cloth or you pre-wet the surface. I usually go with the dry laid because I work alone and getting the cloth to lay right on a wet and sticky surface is a nightmare by yourself. I usually staple it on well then wet out. Pull the staples prior to re-coating to fill the weave. I use a thin mix with cab-o-sil or micro balloons as a weave filler then a final light coat of pure epoxy to seal the surface properly.

[wkisting]

Wetting out first, before filleting, is the best practice. Although it is rare, I have seen three small boat hulls in which the glass applied to a bare wood hull without pre-wetting resulted in the epoxy being starved out of the wood, soaked up by the glass. The same thing can happen with fillets, and this can lead to catastrophic failure of the bond, sometimes literally just falling apart with unbelievable ease. In one case, I saw the entire bottom glass layer on an 18' canoe bottom pull off in a complete sheet about three years after it was applied. It looked like a good glassing job for all those years, but then, when it struck a rock to start the tear and lift the glass a tiny bit, the whole bottom peeled off with only some moderate pulling by myself and my friend who owned the canoe. It turned out the glass had not really bonded to the hull because the 'glass starved the wood and failed to get a good soak-in bond. The first thing my friend said was, "Now I see why I should have pre-wet the hull," and I am convinced he was correct that that was the problem.

Ever since, I always wet out joints or bonding areas first with a small batch of epoxy (just enough to do the wet-out job). Then I mix up a separate batch to thicken for fillets. By the time I'm finished mixing up the fillet mixture several minutes later, the first wet-out is pretty well-soaked into the wood. You don't need the wet out coat to cure before applying fillets; you just need to ideally let it soak in for 10 minutes or so, ensuring that it has saturated the wood well. Once you get the fillets in place, I like to let them firm up for about 40 minutes to an hour. At that point, they should still be tacky and will accept fiberglass tape very well. Be sure to lay the tape down smoothly, though, as it will really stick. The tackiness then holds the tape in place while you wet it out with a fresh batch of epoxy. Use a foam brush or something soft so that, as you wet it out, you do not push dents or irregularities into the fillet. On the other hand, if you come across irregularities in the fillet, it should still be soft enough to push them out carefull with you fingertip.

One last tip: Don't mix up huge batches of fillets at once. The thickner seems to quicken the curing process and increase the amount of heat that the batch will give off from the chemical reaction. It is better to mix several small batches 10 oz. of expoxy or less, than to mix a huge batch that you have to throw away because it becomes too hot to touch (which does happen... sometimes to the point of melting the mixing cup) or cures before you get a chance to put it in place.

[Ray Frechette Jr]

..... Once you get the fillets in place, I like to let them firm up for about 40 minutes to an hour. At that point, they should still be tacky and will accept fiberglass tape very well. Be sure to lay the tape down smoothly, though, as it will really stick. The tackiness then holds the tape in place while you wet it out with a fresh batch of epoxy. ....

I generally lay tape in as soon as fillet is laid down.  It can be done without disturbing fillet shape.

One last tip: Don't mix up huge batches of fillets at once. The thickner seems to quicken the curing process and increase the amount of heat that the batch will give off from the chemical reaction. ...

Most thickeners will act as insulators keeping heat in the mix.  That indeed quickens the reaction.

[Johnny Socko]

Thank you all for the advice. I have been very busy with both work and boat so not much time at messing about.

John

[PAR]

The rule is any raw wood or previously unepoxied surface needs to be "wetted out" with unthincked epoxy, before a fillet or fabric is applied.

The cloth doesn't suck out the epoxy, it's the other way around, the raw wood or dry substrate sucks in epoxy, leaving the fillet or cloth sheathing "starved" for goo. This is a common mistake by folks looking to speed things up or novices.

On surfaces that have received epoxy previously and that hasn't been sanded through (exposing raw material), then no "wet out" is necessary as the surface is sufficiently sealed to prevent resin starvation.