Post cure epoxy

A sail board maker friend of mine told me they used to put laminated boards in a black plastic bag out in the sun for post curing. He said they would get temps around 60 degrees celcius (140 farenheit - 60X9/5+32). Has anyone tried this?

I’m just about to glass an eps board with paulownia wood/glass sandwhich. I can’t get straight answer from the foam manufacturer of its density I think it’s about 1 1/2 to 2 lb sq ft. I’m using an epoxy which is new to me and seems to wet out well, has good clarity and not very prone to foaming and pin holes. It’s designed to be able to cure adequately at 15 to 25 C but better at 60 C (98%) OR 80 C (100%). I’m thinking of trying the black plastic bag method.

It’s got a vent hole. I’m wondering if that’s enough to withstand this heat without anything bad happening. I haven’t post cured any boards before and they seem to hold up alright. But the board seems really light and strong so far with a good springy flex. I’d like to give it a go if it’s gong to make it better. Anyone done this

Jon

just watch your heat distortion temperatures …as a guide a resin can be cured after 24 hours , but not reach full cure till 7 days …

it may handle 50 degrees cured , but will handle 90 with full cure …

what can happen , is your board seems hard and cured , so you post cure it and crank up the heat , but you go over the heat distortion temperature for a semi cured resin , it then softens , while soft it can move under pressure , which means your timber may want to spring back , where you have it situated can cause problems if its unevenly balanced or resting heavy in an awkward spot …

you could come back a few hours later , now its fully cured and hard , but the rocker has sprung out or its twisted …

post cure is the way to go , but dont do it to early …

ive ruined my fare share of boards tweaking the post cure method …

the earlier you post cure the better results ??? the paradox !!!

if you do a handlam , wait for a few days …

if your vacumning , do it while its still under vacumn , then nothing can distort and youve really kick started an unbelievable tough cure …

regards

BERT

Thanks Bert,

I am going to vacuum the glass on. Now you’ve got me thinking. I could make a black plastic v.bag and haul all my gear outside and put it in the sun. Hmm.

Jon

Careful not to go to high or EPS will melt. 185ºF is melting point. Also if you start at ambient temperature and “ramp up” your resin should begin to stiffen as the temprature begins to soften the resin… hope that makes sense. Using a slow ramp up will lessen your chances of warp. Be sure to support the board while elevating the temperature… that means a rocker table. Also watch the heat when your under vacuum… the foam collapses a bit easier when its hot and if your using 1# foam I wouldn’t pull more than 10", I liked 7. I’m not a fan of the black bag method, maybe for post cure on a hand layup after at least 24 hours at room temp. It isn’t hard to build an oven and the control you get in an oven generally gives much better results. I also like a nice ramp down. Don’t pull the board out of a hot bag and stand it against the wall… or put it in a rack, you may warp the board there. I like to turn off the heat and let it cool down nice and slow. Less chance of inner laminate tension that way too.

How would your recommend building and oven?

I’ve seen pics of people’s ovens in the archives somewhere, I think it was for curing AST resin or something, Just build a lightweight box-frame with a coffin lid out of 2x2 lumber, then use some Home depot 1" insulation foam to make the bottom, sides, and lid. seal with tape, and if reasonably airtight, the box should hold heat well, and thus not need a very powerful (or dangerous) source of heat. the ones I saw used lightbulbs and a fan, and one used a hairdryer. If you are feeling industrious, you could wire in a thermostat for pinpoint control.

Wells

PS bert, gimme a break, would you?

I just managed to scrounge up a fridge vac, some tubing, and tested out some vinyl for a bag from the local plastics suppliers (crushed a few cans, cooooool), cobbled together a hotwire, got some balsa from the hobby shop, tried some layups, my apartment is overflowing with piles of crap and scary devices, girls I bring home are frightened off, stuff is stuck to my cats, and now I’ve got to add a homebuilt autoclave to the mix? Sheesh…where the hell do i put it?

Next thing, you’re gonna be telling me that nuclear irradiation is the way to go…Know any good strontium suppliers?

Quote:

How would your recommend building and oven

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I’ve seen/made anything from a super elaborate 150" oven for carbon fiber masts to an EPS sheets duct taped together with a space heater and a candy thermometer stuck through the EPS.

Of course safety is a huge concern, so keep your eye on it!!

Here:

http://www.swaylocks.com/forum/gforum.cgi?post=191862

Thanks for the link. I had to laugh at your Bert comment. I feel the same way. Just when I think I’ve go it figured out he throws some new thing into the mix. Its a good thing that I like making toys (autoclaves(heatbox) etc…) or I would just give up. I need to figure out a way to regulate the temperature.

A couple of weeks ago (months?) I read, here, about using an electric blanket to heat up the lam for a vac’d board. Could we wrap an electric blanket around a finished board (or during the lam) to, not only, rapidly finish a board but also to ‘cure’ it?

If yes… time sequence, temp?

Can’t wait to get started with my first (fifth board total) 1#EPS/epoxy/carbon/balsa composite board! Number 4 was 2# EPS/carbon/epoxy 10’… rides like a DREAM! Lighter IS BETTER! Carbon rail stringers kept it light and flexable enough yet it’s strong!

Les

I’ve been using System Three SB 112 (epoxy resin made specifically for surfboards) for about a year now.

System Three makes epoxy resin primarily for the boat building industry where post curing epoxy is a requirement, and their web site at www.systemthree.com has some good information on post curing epoxy. Apparently it is possible to post cure epoxy in a very low tech manner (e.g., in a van parked in the sun, using a cardboard box and space heater, etc.), and the System Three web site discusses how to do post cure and gives some interesting examples (e.g., post curing a 30’ spar with a cardboard box and space heater).

Anyways, I was curious as to whether or not it was necessary to post cure SB112, so I emailed them my question, “Is it necessary or desirable to put the SB 112 through a post cure heat cycle, such as described on the System Three web site?”

Their answer: “It is not necessary to post cure SB-112.”

I don’t how this might apply to other epoxies besides Systems Three.

I’ve also noticed that even though epoxy cures to a sandable state in about a week or so, it also seems to continue curing (i.e., hardening) over a longer period of time as well, even without the benefit of a post curing cycle.

Just curious, I have heard a lot of people say that it is better to post cure but is there really a difference in the end quality or does it just speed up process so you don’t have to wait to use the board?

Joe~

I’ve wondered the same thing, but my boat building and sail board building friends do it and the mfg recomends it so there must be some benefit. I think I could easily my rocker table for this. I’ll try to post a picture when I do this but I’m clueless with the digital camera.

Post curing surfboard epoxy undoubtedly makes the epoxy stronger, but I think the question here is, is it necessary (as opposed to merely desirable or beneficial)?

The reason post curing boat epoxy is an absolute necessity is that boats undergo much more severe stresses and the consequences of epoxy failure for a boat are far, far more serious than they are for a surfboard (unless you are towing in, that is!).

Bert,

Can I post cure a epoxy laminate before it gels? I will be putting them in an oven with a temp of 150° F. What should I be looking for with the Styrofoam blank and a Clark ultra lite blank? Will the SB-112 run off the board if I put it into the oven to soon? Will my free laps drop of the bottom of the boards. Any info or instructions will help avoid a disaster

Thanks for your help.

Timmmyyy

Howzit NYsurfer, I would lower the temperature for a styro blank to about 135 degrees and leave it in the oven a little longer. Styrofoam will weaken and even possibly melt after a while at 150 degrees where a poly blank can take the 150 degree heat. Just something I learned from the AST info they sent me.Aloha,Kokua

Hey Tim, when i do my boards, i lay on the epoxy and put them right into my home made autoclave type thing very similar to what is described above in the thread although i use ceramic heat lamps for warming reptile cages from the pet store as a heat source (one in each end) i don’t know what type of oven you are using or really how hot 150F is but i get mine up to 40 celcius and then unplug one of the lamps to let the temp slowly drop to about 30 celcius. after 2-3 hours epoxy is hard enough to flip and work the other side or scrap out any bumps(works better than sanding) once the epoxy has started to gel or set, it won’t go back to liquid at least not before the foam does. Another thing that has worked for me is to heat up an EPS blank for a 1/2 hour or so before you lam it, to get all the air insde to expand and this seems to reduce air bubbles in the lam when you do heat it.

hope this helps.

cheers

We have a heat box, but the laminators got too antsy and tried stuffing epoxyies into it as soon as they were finished flipping laps. The board has to have gone off first before trying to heat it up, I don’t even recommend micro waving the resin before laminating, I did one board this way and it nearly bit me on the ass, it is over a year old and I haven’t sanded it yet, it has never been in the sun and has yellowed very much

Kokua,

Thanks for the info. I will give a run down on how it went on a later post. Pictures will follow.

Timmmyyy

Pat,

Thanks for your tips. I am tired and do not have the time to let you know what I learned today from post curing epoxy. Lots of interesting problems with the two types of boards. I also laminating a 9’ board with polyester and a deck laminate of Carbon/Kevlar. Interesting material to cut. I will take pictures and post them soon.

Timmmyyy