One of my students was preparing some Dookie Shmutz to fill small cracks and checks in his canoe. As I'm never sure of my student's level of experience with epoxy, I always make sure to let them know how to mix the epoxy. The epoxy in question was West System's 105/207 system and the ratio is 3:1 epoxy/hardener. The pumps that are sold by West System for the resin are metering pumps are sized to dispense the proper ratio with a single pump from each container.
I told the student to dispense one pump each of resin and hardener until he had enough volume, then to mix in the wood flour and silica until he had a mixture that was the consistency of creamy peanut butter. I was then called away to help another student. When I returned, he had what appeared to be the proper mixture and was applying it to his hull.
The next morning, we came in to put the canoes back in the barn. The filler on this canoe was not setting up - it was like soft putty. Sometimes it is a bit cool in the shop and the epoxy takes a little longer than usual to set. As last week was a vacation week, there would be no other classes in the shop, so we left it in the shop rather than take it to the much colder barn in the hope that it would cure.
Yesterday, we arrived to find the filler on this canoe stiffer, but not fully cured.
When the student came into class, I asked him how he mixed the filler. Turns out he'd read the can about the 3:1 ratio after I told him how to mix the epoxy and used three pumps of epoxy to one pump of hardener.
Thotful spot time.
We ultimately resolved to scrape what uncured filler material that we could and to wipe the hull with denatured alcohol. Once this was done, we applied properly mixed filler.
This morning, the filler had set up hard. We appear to be in luck!