UV hotcoat

General Discussion
1

I decided to try my UV hotcoat without catalyst because (1) it was really sunny today and (2) I was curious to see how well it worked. I usually add 0.5% to 1.0% catalyst.

My little experiment was interesting. The UV hotcoat gelled up very nicely, as usual. After two hours in the sun I decided to sand it. It seemed rock solid. Well the UV hotcoat sans catalyst gummed up my sandpaper like a lam coat. I’m usually able to get through the rails with one piece of 50 and the deck and bottom with one disk of 50 on the power sander. Not today. Three or four sheets each of 50, 80, and 120 and I’m ready to gloss coat. UGH. I’d imagine that the resin will completely harden up by tomorrow, even without catalyst.

I pledge to add catalyst to all UV resins for now on, unless it is for spot ding repair.

2

funny never use MEKP in hot coat with uv, stuff cures in like 3 to 5 minutes in the sun ok 10 ready to sand everytime maybe forgot to add surfacing agent? put it in direct sun and did not remove in about 30 seconds to allow the wax to rise to top of coat? only time you need to put mekp in uv is if you are doing tints. or plugs boxs etc.

3

so if your are going to use catalyst mekp why spend the extra dough on the uv cure ?

4

did you have pigment in it.

also you may have left it too long in the sun. it got too hot. how long was it out of the sun before you started sanding ?

5

Howzit pierpont, I think most builders like the UV for laminating, But you still need catalyst for plug and box installs. I use catalyst for hotcoats then put the board in the sun to cure after about 10 minutes after it kicks. Don’t waste any sand paper this way which can add up if the UV hotcoat messes up and is gummy. Aloha,Kokua

6

Scott’s right about short exposure to the sun. I set mine in INDIRECT sunlight for several minutes to allow the wax to rise. Once you see the film on the surface, it can be moved into direct sunlight. If you place the board in DIRECT sunlight imediately, the wax will be trapped inside of the resin causing it to gum-up your sandpaper.

I learned this the hard way a couple of boards ago. ;(

7

what SrPato said, always let the wax rise first. For me, the board sits in the garage wile I clean the brush, etc. Only then drag it out into sunlight.

I dunno if lam resin plus surfacing agent plus MEKP would cure fast enough to sand in a couple hours, anyway. The board presently awaiting finish coats in my garage sat for several days before I sanded the hotcoat. It’s a birthday present for a kid, he won’t get it till October, why rush?

Hate sanding. Last night as I took off the respirator I noticed I still had the charcoal cartridges on, rather than the HEPA filters. Now I’m gonna die, but the board was sanded well enough.

8
Quote:

did you have pigment in it.

also you may have left it too long in the sun. it got too hot. how long was it out of the sun before you started sanding ?

That’s it. It was quite hot when I began sanding. Thanks for the sanity check!

9
Quote:

so if your are going to use catalyst mekp why spend the extra dough on the uv cure ?

Flexibility and certainty. Often I cannot glass during the days because of work/family conflicts. But if I screw up the catalyst mix on the light-side I can always leave it in the sun and guarantee a cure. And for someone like me who does two or three or four boards/year, the cost effects are negligible.