Does a hot coat have to be 'hot'?

Hot coated my first board last night - pics to follow once its been fin plugged and sanded - but despite mixing it at 3% catalyst it took AGES (about 20 minutes) to gel hard enough to let me pull the tape (and it was still only jelly - like). This was probably because it was cold in my garage in the South of England (about 10 degrees C, or 50 F)…

Question is, for the next board, is the long cure time on the hot coat a problem, should I shoot it even hotter, or just wait for the weather to get warmer!!

Thanks

Chris

PS without Swaylocks, and mostly learning by lurking, not sure I’d have got as far as hotcoating!!

With that low temperatures, I think you should use some sort of heating in the garage to get more predictable results. Still, the reason it’s set of hot IMHO is to prevent it from running off the board and exposing the weave, especially on the rails. Unless the resin doesn’t get hard or weave is exposed all is well. If you’re a little lucky the resin was a little thicker, enough to cover the weave and not run off due to the low temps.

regards,

Håvard

A slow cure is a good cure. Remeber it is a chemical reaction and, provided that you are using good resin and catalyst, will eventually do its thing.

Do not add more catalyst as this will only weaken the strength of the resin and make it very brittle. Think spider cracks and worse.

50 degrees is about as cold as you would want to go with finishing coats. A portable space heater in your garage to warm things up is a good idea. Also keep your board in the house up until the last second before you put any resin on it as actual board temperature can play a big role in having the wax in the resin rise appropriately. And of course keep the resin in a heated area as well.

In colder weather the resin will not flow as well. In this instance it is very tempting to overbrush it. Again, let nature do it’s thing and let the resin flow to where it will eventually flow. Overbrushing will inhibit proper wax rising.

Drew

Drew got it good. A hot coat doesn’t have to be hot.

Let’s review a little history, this is how it was given to me: the term “hot coat” was given to this step in the process back in the day, because you did in fact want it to go off quickly, and resin generates/releases heat when it cures.

The reason for a quick cure in the old days was that the function of the hot coat is to fill the weave of the glass which is left from the laminating, and so you can have a goodly thickness of resin to sand and smooth out. Remember, in those days glass was 9 to 12 ounces - must have been a gnarly weave! So, to fill all that weave, and not have the resin run off the board (resulting in an inadequately filled weave) you set it off quickly.

Nowadays, with UV curing almost instantly when it’s exposed to direct sunlight, and lighter weave, the trick is (at least around my garage) to brush it out with the doors closed, then let it sit for 15 minutes to allow the wax to rise, and ONLY AFTER THAT take it out into direct sun for the setting and curing.

As written in posts above, a cold day really slows down the cure time. I don’t know if coldness so drastically affects UV cure, but it might be a way around cold weather limitations. The information I have seen suggests that poly resin is strongest around a 2 percent catalyst/resin ratio. I know I can’t go that strong in my weather (mid 80s), when catalyzing I am at .8 percent or so for a lam, maybe 2 percent for hot coat and finish coat, if I use catalyst at all any more.

I’m in the same boat as you.

Pre heat the resin to about 20 C. Just leave it indoors all day (in a well sealed container)

If you can get a small air heater for the garage. This will make a big difference.

Brian - Ireland

i have to deal with cold glassing…but i have a good method for keeping things a little warmer. i use a small ceramic heater, and keep it low next to the resin and s/a if hot coating. when s/a gets cooler it tends to clump up and really f’ up your hotcoat or gloss. you only need to heat it for a few . use the mixing stick and “play” with the resin until it’s at the right consistency. you should have an idea when it’s right. it keeps the coats a little smoother when laying out…

20 minutes for a catalyzed hot coat to gel doesn’t sound that long to me. If it cures to a sandable hardness by the next day, don’t sweat it.