No one around here at any of the hardware stores has ever heard of Cavosil - so what should I use with the hot coat?
Bryan,
Personally I don’t know why there is this grass roots thing to add Cabosil to Hot Coat? Hot Coats are probably the easiest part of the glassing process. As long as you have pre smoothed your lam, i.e., razored all the bumps and strings down, and hit the smaller spots with a surform getting it smooth, just tape and then paint the hot coat. 1 quart resin to about 8-10 cc MEK, work time about 20 min. Make sure your room has no circulating air or breeze (wear your mask or die). Paint the hot coat, put it on tip to tail, then go side to side tip to tail, then lightly tip it out tip to tail. Now run your brush lightly around the tape line, then walk away, don’t fuss with it, it should self level if you evenly coated by the process above. By the time you clean up your brush it should almost be time to pull the tape. It’s all in the process, smooth shape+smooth lam job+smooth hot coat=Easy sanding.
-Jay
Brian, If you’re wanting wax in your hot coat you need to add some wax in styrene, sold by most composite suppliers. It’s called something else like surfacing agent in the US I think. The cabosil you’re talking about will not put a sandable surface, but will thicken the resin, and make it harder once cured, but isn’t essential, also sold by suppliers. Have fun.
Cabosil is a just brand name for what is actually Fumed-Silica. I don’t think a lot hardware stores would keep it, as it’s kind of a specialty item. If you’re not near a surf shop supplier, you might find it at a boat repair store (fiberglass work). Chemical suppliers that’s are geared towards pharmacuetical products would also have it. I listen to the guys above and not add it.
You do need to add sanding agent (styrene/wax) though as they have said.
Best,
Herb Bean
Further on that - cabosil/aerosil is a white powder, like flour in appearance, and all it does beyond thickening the resin some is kinda cloud it some - add enough and it can mimic foam for repair work. If it’s got lumps in it, you get a lumpy mix. Dump some corn starch into a glass of water and you’ll see what I mean, corn starch and water behave a lot like resin and cabosil.
It doesn’t wet out and become transparent like cloth does. As Jay said, there is no reason to use it in a hotcoat and plenty of reasons not to. Just follow his ( complete and excellent, by the way) directions and you’ll be fine.
hope that’s of use
doc…
There’s always been some discrepancy in catalyst amounts, I’m sure something to do with temps, different resin brands, but it must also have something to do with MEKP quality… but that’s way off my numbers.
I hotcoated up my latest last night with my usual mix: 30 cc MEKP to ½ qt. Lam resin with 20 cc S.A. I measured the temp at 19C, a little cool, but not that far from 70. No exothermic reaction… I’ll use the same formula in the summer and get the heat. I’ve had no probs with the Hotcoat, as you said, it really is the easiest part… but I’m curious as to the difference - seems pretty significant. Hell, I shoot my lam for glass hotter than that (12 – 15 per quart)
-hey Bryan, you can put or not aerosil in your resin…, but if you do a ligth and more consistent glass job you should put it. more if you do a sanded hot coat finish or spray finish with 4 oz cloth…
-also you can put colloidal quartz…
-some peoples copy methods an not adapt others.
-if all your life glass boards with heavies volan clothes 2 or 3 layers on the deck, do thickers hot coats and also gloss, you may don´t understand why you should put silica in your hot coat.
- also you save money purchasing a good laminate resin and add wax styrene and silica or quart to make hot coat…
-it´s more difficult to sand, but easy with a grinder…
rKelly, if my calcs are right ( I’m in australia and not used to imperial measurements) you are catalsing at 5%. That is a lot of mekp. I relise that the temp is low. What gell time are you getting? If you have to add that much mekp to get a quick gell time, you would be better off getting some resin that is promoted higher so you don’t have to use so much catalyst. I go at 2.5% @ 25deg C. I think that is about 78deg F. By the time I have brushed it out and washed my brush I’m pulling the tape. Probably 10 minutes max. In winter I go the same % but I’ll waite a while before I start brushing the hotcoat on. Too much mekp will cause porousity if it gells to quickly. Not a good look on a gloss board. Platty.