Do not thin epoxy. All of the epoxy manufacturers recommend against it.

Your MAS epoxy is already low-viscosity. If it begins to thicken after a few minutes that means it's beginning to set. There are a couple of things you can do to slow it down. The most obvious is to use slow hardener if you aren't already using it.

The shape of the container you use to hold the epoxy while you apply it can be critical. Your mixing cup is not the right shape: Epoxy generates heat as it sets, and this heat accellerates the setting process. Holding it in cylinder concentrates the heat, causing faster setting. You want to spread the epoxy out in a flat container. I used paint trays when I was brushing/rolling on epoxy and got about a half-hour out of a batch.

CLC carries the "spread out the epoxy" to its logical extreme. In their shop tips on fiberglassing they recommend pouring your batch right onto the boat and spreading it out with a squeege:

https://www.clcboats.com/shoptips/epoxy_and_fiberglass/fiberglassing.html

That's what I did and it worked fine.

   Per MAS you can thin epoxy with denatured alcohol. A little bit goes along way and there is alot of discussion on this subject on this forum so I won't go into a long discusion. I have used it when the temperatures are low 60's (read thick) with success. I don't apply epoxy below 60 degrees (70's are great). Lastly: keep the epoxy ithe house vs leaving it in the garage. A paint tray as Chenier recommends is smart to keep it from setting so quickly and thickening If I need to apply alot of resin, sometimes I dispense just the epoxy into multiple fresh cups (no hardner) then add the hardner along the way mix and use. 

BTW. Loved your small batch 10 pumps! 

Dean

Chenier posted:

"All of the epoxy manufacturers recommend against it."

This from a MAS tech fellow after I inquired last July with this same question:

"Denatured alcohol works well for thinning LV resin. You can also use xylene which works very well and I know a few users who actually spray LV by thinning it down 15%. Acetone also works but I understand your concern with it’s flammable nature. Make sure you don’t add more than 15% to the total mix ratio of epoxy which could potentially weaken the structural bond of the epoxy. " 

BUT the big caveat is: be prepared to deal with the consequences.

Thinning epoxy with a solvent puts an admixture onto your project. Some of both go into the porous surfaces with the first application but consider that all the rest of the solvent has to go somewhere else over time.

What happens is that the solvent molecules leave minute pores in the cured epoxy matrix. This may not be a problem with a car body or motorcycle fairing but with a wood-cored boat it most certainly is. Left uncovered, or poorly covered with later unthinned coats, those pores can allow water to reach the wood underneath.

Here's a link to a good presentation about dealing with 'pot life' and epoxy application. Good tips init for working with this stuff so it does what we expect it to do.

Kent,

I used thinned MAS resin to help wet out the glass cloth on the outside of the hull on my Peeler Skiff. I used acetone and was very careful about ventilation and sparks. If I were to do it again, I would use the much safer denatured alcohol. It made covering the hull much easier and has so far lasted 7 years, moored all summer on saltwater, without problems. I would offer a few points of caution:

1. Used thinned epoxy only in well-ventilated areas.
2. Make sure you squeegee off any excess thinned epoxy. I've noticed that when epoxy sets before the solvent has fully evaporated it can end up a little rubbery.
3. After the first coat has set (and the solvent has fully evaporated), use only unthinned epoxy to fill the weave (also filling any possible pinholes left by solvent evaporation).

Cheers.

-Dick-