Expanding on an earlier post about hotcoating and the additives:
I do a lot of work outside and have had a problems with my hotcoat (not setting/tacky) at times. Jay mentions in a previous post that no air should be moving and I’ve seen that advisement before.
What happens when air moves? Is it evaporating the catylist or my sanding agent? At times I kept uping my catylist ratio to no avail. Another note though - when I’m using UV for a hotcoat, I never have any problems working outdoors.
Expanding on an earlier post about hotcoating and the additives:
I do a lot of work outside and have had a problems with my hotcoat (not setting/tacky) at times. Jay mentions in a previous post that no air should be moving and I’ve seen that advisement before.
What happens when air moves? Is it evaporating the catylist or my sanding agent? At times I kept uping my catylist ratio to no avail. Another note though - when I’m using UV for a hotcoat, I never have any problems working outdoors.
Thanks,
Herb Bean
Ok, what might be happening ( and I expect Jay has a better handle on this than I do ) is one of two things- either the sanding agent is being blown around some ( it’s a thin film, after all, like soap film) or else it’s being cooled down to where it’s not going off, though I’d think that eventually it’d kick off. Try adding more sanding agent/wax, that might help some. Certainly can’t hurt…
So to understand the process/relationship of wax and styrene: Under good conditions (no wind), the styrene evaporates slowly bringing the wax to the surface while everything is kicking. And on windy days, the styrene is evaporating before the wax has a chance to get to the surface.
Is my ‘lack’ of problems with UV due to it kicking so fast. i.e., styrene evaporting and glass kicking at a more equal time?
Exactly, I don’t know what happen chemically but, just through trial & error when there’s a breeze in the glassing room you get lumpy runny rails, sometimes you get tacky spots that don’t kick, just all round grief. Another problem is if you fuss with the rails because you went too heavy on the Hot Coat, and didn’t get it level to start with (level meaning, consistent thickness on the entire board) you keep on running the brush around the rails to smooth out the running blob of goo. You brush out all the SA wax and you never get the rails to kick off. Get it covered, get it level, and leave it alone, give it time to self level and let the wax rise to the top.
"The unsaturated polyester formed by condensation polymerization is added to a mixture of styrene (a crosslinking) and peroxide (radical initiator). Radicals attack the unsaturations in the polyester or the styrene vinyl groups to initiate a chain polymerization reaction which yields a crosslinked styrene-polyester copolymer. Styrene provides the crosslinks between the polyester chains to form a thermoset polymer. " http://homepages.ihug.co.nz/~layla/polyester.htm
So, in the presence of a peroxide catalyst/initiator (MEKP) that provides free radicals, styrene monomer chemically reacts to cross-link polymer molecules within a resin, transforming the liquid-like mix into a fully cured solid product.
It makes sense that if the styrene evaporates quickly (from too much air flow across the surface), the cure would be incomplete, perhaps lumpy.
It also makes sense that too much styrene could result in a brittle cured resin - have seen this comment offered as an explanation for why some gloss coats crack easily – the glasser added too much styrene in an attempt to get good flow…