just lookin for any glassing advice in general. i am glassing over eps foam . and am under the asumption that i will need to use epoxy resin? i heard that plyester will react with the eps and not work. help please
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The epoxy resin would work best. Good luck…
poly is too hot for EPS…it’ll melt the foam.
you have to use epoxy resin - found out the hard way on this one. One other word of caution that I learned the hard way - it takes almost two days too cure enough to sand with a sander/grinder(depending on temp/humidity). If you sand it too soon it gets hot and will gum up and look terrible. The gum is difficult to remove also.
I have found that to be the only big drawback to epoxy resin - otherwise I love it. On the same note - do you know if it’s okay to use polyester resin(suncure) on clark blanks? I have a bunch of blanks that I need to glass and I am under the gun. I’d love to use suncure to speed up the process but just want to make sure that it won’t damage the foam.
thanks
I am no chemist, and please correct me if I’m wrong, but I’d say that “hot” is not the point. Isn’t styrene monomer (which is one of the components of polyester resin and plays a big role in its polymerisation) actually a solvent for EPS (Styrene/POLYstyrene)? No offense intended, of course, just want to get it straight. O.K.?
I think you are correct about the chemistry of the two substances - but the end result of combining them is the appearance of melted foam.
An ammendment to my previous question -
can you use epoxy resin on clark blanks? I have never done it and have 3 gallons of epoxy that I would love to use up but am concerned about compatibility.
thanks
Go ahead, nothing will happen. Only the opposite can’t be done. Many people say that epoxy is way stronger than polyester, and there is no compatibility problem between epoxy and polyurethane foam. Epoxy is way thinner, too, and thus provides a better bond with foam, infiltrating every micro-cavity it will find on its way. The only back-up is a higher cost, but since you have some on hand…
hey hsh. are you sure that your mixing your epoxy correctly? i have found that i can sand epoxy after aboat six hours no problem. i am in hawaii so there is a fair amount of moisture in the air. Not sure what epoxy your using but remember 4:1 doesn NOT mean, say, 3oz part A and 1oz part B (making 4 total), it means 4oz part A and 1oz part B… try reread the directions, just a thought (i did it wrong a few times)
And of course you can use suncure on clark blanks…
Quote:
I am no chemist, and please correct me if I’m wrong, but I’d say that “hot” is not the point. Isn’t styrene monomer (which is one of the components of polyester resin and plays a big role in its polymerisation) actually a solvent for EPS (Styrene/POLYstyrene)? No offense intended, of course, just want to get it straight. O.K.?
i’m no chemist either, but i’m fairly certain that styrene momomer was actually one of the primary components of expanded polystyrene. how, then, could it be a solvent? i thought it was the MEKP catalyst added to polyester resin that generated heat that literally melted the EPS foam when in contact with one another for enough time, rather than dissolving through it. MEKP is a thermoset catalyst…more catalyst = more heat (hence the name “hot coat”, which is generally catalyzed hotter than the lam.). like i said, i’m no chemist…and truthfully have no basis beyond the fact that it’s what i’ve always thought…i just never questioned it before.
Any chemist around? We need your lights! Not that it matters so much, anyway, since we all agree that EPS will melt under polyester. But just out of curiosity, is it a chemical reaction (styrene/polystyrene) or a physical reaction (polystyrene being a thermoplastic -not thermosetting- melts under the heat generated by MEKP)?
The styrene and the polystyrene disolve each other. It would be like adding water to ice. The water is going to melt the ice.
jjp - thanks for the advice. I wish that was the problem though. The epoxy I’m using is a 2:1 mix, ie. I use 12 oz. resin and 6 oz. catalyst - sound right doesn’t it? I have tried a bunch of different epoxy companies and have had pretty much the same results across the board - West System, Surf Source, Progressive
.I am in Maine(ie. significantly cooler temps than Hawaii - the last “H” stand for hypothermia) so that could be part of the issue. On the other hand its warm here now and I have the same problem.
Oh yeah - I do know that sun cure will work on clark foam - I wrote the ? incorrectly. But now that I brought it up - have you ever tried suncure over epoxy? Example - laminate with epoxy and use Suncure for sanding resin? I think I could cut my “waiting to cure” time a lot that way.
HSH,
Maybe I’m nit-picking but…
You don’t need sanding resin with epoxy. Epoxy should dry sandable every time. A ‘fill coat’ might be desired to allow you so sand more without digging into the weave.
Using suncure over epoxy may work, but it will not have the chemical bond between poly and epoxy that you’d get if you used epoxy for the sanding/fill coat. I’ve heard that a poly fill, or gloss, coat can peel from an epoxy lam. I havn’t tried it myself though so it’s second-hand info.
hope that helps…
Eric J
thanks for the advice - I guess I’ll just stick to the epoxy. I do find that it is sandable every time - perhaps I’m just looking for a shortcut that isn’t there. The reality is I probably just need to spend more time behind the sander to get the finish I want. Sanding is my least favorite part of the process - no shock there, eh?!
I do wish that I could explain why my cure times are so long.
thanks for the help
Chris
I agree totally. Sanding can be the worst part of the process. All I can say is seeing a well sanded, smooth as a baby’s butt board is a good reward for all the work.
Epoxy curing - I’ve only used Resin Research epoxy which worked excellent and dried clear, rock hard, and in a regular time frame (using the fast hardener). I think you could get away without polish if you got a good smooth coat of RR epoxy on after sanding - it’s pretty shiny. I’ll be trying that in a few days on a few mini-longboards. Hopefully I’ll get to take a few pictures of them and post.
Best,
Eric J
I’ve used a lot of epoxies too, and you’re right, sometimes they take a long time to dry. Worth it every time, though. Just be patient.
Poly hot coat over epoxy will work, but can chip off - not necessarily peel. As I understand it, the poly hardens much more brittle, while part of the durability of cured epoxy glass is that its somewhat flexible.
Howzit Benny, The poly doesn't adhere to the epoxy very good and I've seen areas just detach and pop off from the epoxy just from flexing. Even though epoxy is a B#*^h to sand, I'd use it for the fill coat. Aloha, Kokua