Epoxy full cure how long

Hey guys,

just want to clarify something…

Will epoxy reach full cure after “X” amount of days with out being postcured?

and does a post cure oven essentially just speed up a sequence of inevitable events?


It completely depends on the epoxy system you have, the hardener used, and what you consider to be ambient temperature.

There are some long pot-life resins that will never reach full strength, even in warmer climes.

Generally speaking, most of the “ambient temperature curing” epoxies we use will fully cure eventually, for most intents and purposes.

Still, postcuring is a very useful tool.

I’ve said it many times, but most of the issues people come across with epoxy is due to working it when undercured.

Cure it hard and it will sand like a dream, and be tough as nails.

Wash cured lams with water to ensure no blush, and you’re set.

For example i’ve found that Kinetix epoxy goes through to a pretty good cure quite quickly, but it really helps to give it a bit of heat, to get it to a proper cure that allows you to sand it without smearing, and to get poly resin to stick to it. It seems to stall at a “nearly cured but not quite” stage… kinda wierd

Hey Guys

I use the kinetics and the guys there told me it cures a lot better and crisper with a post cure.

I have a blow heater that I put on in my insulated shaping room and it gets to about 45 degrees C and I leave it for about 8 hrs.

Have had fairly decent results, but still doesn’t sand like poly.

Takes me a lot longer and gums up the pad a bit


Hi Moonfish,

Yeah I have been using RR epoxy for a while now.

Post cure is worth it. Gives the board a real crisp feel and polishes up nice.

I just cook my boards in My MDF oven - looks like a coffin - heated with an old electric blanket. Setting number two sits the whole thing at 55 F. 6 hours and its done.

Can use the car on a hot day but you need to watch for overheating and adjust the windows accordingly. Low tech and free!

Hows the boards coming along with that VH foam. I just finished a couple of fishes and a shorty. I found it easy to shape but I did still seal the blanks for cosmetic reasons.

thanks for info kit, that makes alot of sense. i had thought as much but wasnt positive.

offshore, i am just putting the finishing touches to my first one now. shaped all good tho. have done some weird shit to this one bit of a learning curve you could say. will post up a pic when its complete. taking it to kaikoura next weekend so will give ride report also. its a copy of a compsand board. this one is feeling prity light too.

how yours riding?

I don’t take any chances… I’ve made the mistake before, more than once.

I use RR and don’t postcure, but should. Instead, I give it at least a few days at room temp. before I sand, and SIX FULL WEEKS at room temp before I ride it. I’ve rushed it and ridden it too soon and had them break. I’ve tried to cure for several weeks, but at temps too low, and had them break. Best thing is to postcure, or just keep it in a heated space and forget about it for a month or two.

Hi guys -

Regarding post cure… some epoxies appear to cure at room temperature but when exposed to higher temperatures later, they can soften. From what I understand, one of the benefits of post cure is that it allows cured epoxies to withstand higher temperatures without softening.

I have some kayak paddle blades that were post cured under heat and pressure and they literally ring when tapped. No amount of sun seems to soften them a bit. I also have some fin layups I did using epoxy (no post cure) and if left in the sun, they can get pretty limp.

I haven’t tested any real boards to confirm this… I suspect that at least some of the bubble/delams that have occurred with “epoxy boards” were a result of heat induced softening as well as internal pressure when boards were left in a hot place like on top of or inside a car.

If a board is post cured to 125 and heats to 100 in a car, no problem. If a board reaches 100 degrees in the car but was room temp cured at 70, there might be a problem. As the epoxy softens, it might allow delam under pressure.

This obviously does not take in to consideration other factors like foam density or venting.


Hi john,

thats the thing im worried about. if you cure at room temp does this mean your board is only good for that temp and below?

or will heating it say in a hot car actually make it soft but then it will harden up again afterwards and be good for higher temps. (if it doesnt kill your board)


“thats the thing im worried about. if you cure at room temp does this mean your board is only good for that temp and below?”

Not necessarily - Just that the physical properties of the epoxy may change. I don’t know - maybe repeated heat exposure cycles eventually serves as a post cure?

“or will heating it say in a hot car actually make it soft but then it will harden up again afterwards and be good for higher temps. (if it doesnt kill your board)”

Heating in the car may serve as a form of post curing. From what I understand there might be an optimum time frame and “ramping” or cycling process to the post cure phase.

Bert Burger and others have also described problems encountered during post cure… I.E. bubbles/delams/EPS meltdown, etc. I think it was Bert who advised monitoring heat and maintaining vacuum during cure process to avoid issues described above.

A photo posted on a recent thread about a broken Surftech showed some EPS bead weirdness that may have been (IMO) a result of borderline heat used during cure process. It would be a good idea to know your particular epoxy manufacturer recommendations, the heat tolerance of your foam and to vent the board and/or apply vacuum during cure if you decide to do it.

Well - Hope Greg L. jumps in, at least about RR…

My experience: RR “slow,” same board in the lap thread, I sanded the next day @ 20 hours later… been in the shed @ 70-80 F - no problems.

As for the full on wait until ride… who knows… I end up waiting a week or two from lam date, as I piddle around w/boxes, caps, edges, loops, etc. But, haven’t had any problems…

the only time i have had issues is when i have applied heat to a eps board after fill coat, it blew up lots of little bubbles. crap. wont do that again.

but i have been applying heat after the hot coat cures enough on the last 2 boards, that does seem to give me a crispier harder feel after a similar ammount of time than leaving it at an ambient room temp.

also have been trying the old epoxy in to the microwave trick and this has helped my glassing finishes heaps. it is generally bellow 20d/celcius here and the visco of any epoxy starts to get tested specially in winter. before that i was adding solvent to get decent results but it would take longer to kick into a full cure.

if any guys are reading this in colder climates please try the microwave trick, use a slow hardener too to get a lil bit more time, but really give it a go. it works really well. the surface tension is so much better for fill coats/gloss etc levels out prity damn good.

kit, mds, offshore, john and taylor do any of you guys do this?

Yeah, microwave is great. I live life on the edge, and zap my resin and harderner together, mixed. Nobody should do this. so I don’t get in trouble for recommending it :slight_smile:

I just like it to kick really quick for some apps.

With the hardeners we commonly use, there is absolutely no need to postcure higher than 40 degC.

Unless you want to shorten the postcure time from 8 hours to 5 or somethin.

The mechanicals will be fully there after 8 hours at 40 degC.

You need to vent the board, but thats all.

You should not have any problems with the board distorting or anything, as long as you don’t postcure too soon.

What happens is that the heat distortion temperature (HDT) of the resin increases as the resin cures more and more.

If the resin is still slightly “green”, the HDT could be as low as 40 degC, so when apply heat the resin could go all soft, and distort.

Start your postcure the next day and you’ll be fine.

Some of the epoxies I use have a final HDT around 95 degC, which is much higher than the EPS can handle, around 80 degC.

The cool thing is, that an EPS board with a goretex vent can actually be left in a hot car without worrying.

Unless it gets over 80 celcius, which can happen…

Hello Moonfish…

I don’t have the answer to your question…as a joke I named my workshop the “Low Tech Lab”…Swaylocks friends now have the “Rat Turb Lab” and the “South Bay Lab” and the “South Bay Lab North”…It’s all for fun

I did an internet search…Celsius is the same as Centigrade

40 degrees C = 104 degrees F…20 degrees C = 68 degrees F

I glass and cure at 20 C…I’m a bro not a pro…Lam and hot coat all done in less than 24 hours. Boards sit for 4-6 days before power sanding…No delams so far…over 20 boards glassed with EPS / Epoxy…no real postcure…

Think about this…How much heat is involved in power sanding??? What about grinding down the fin boxes…

All that work and I have a soft spot near the rail after powersanding…

Most Pros will say PostCure is best…My friend had a Surfboard Meltdown during postcure…Ugly…

My boards are good ,…LowTech for sure!!! No delams yet…very strong…not perfect… summer is best for epoxy…


put it up in the rack and leave it for a week or so

I should have mentioned that both boards I’m taking about where 9’2 HP longboards. Both had PLENTY of glass. Same thing happend to Greenlight Brian not too long ago. Rode it too soon and came home with two pieces.

great advice here from all,

A few more tips I have …

Don’t post cure too early - you seem safe after 5 days at 20 C - then cook it!

dont touch or put pressure on the board after post cure until they cool down - they are soft and easy to pressure ding

Cool them down slowly

Microwave is king during winter to keep the resin flowing, so is a warm lam room.

Pre warm the board in winter ( less than 20C) especially for gloss and fill coat. The warmer the board the better the gloss. up to about 35C

Lam on a falling temp If you dont want bubbles (especially with 24kg/m2 or less foam)

Slow sander speed and keep it moving to avoid heat build up on “green” resin if you are inpatient and can’t wait (like me)

Hey thanks for the input guys its appreciated.

offshore, i think these are some great tips. and i definately think my main cosmetic issues come from having to cold of a room and hence surface to fill or gloss on. lams are not an issue its only when i do a fill, some minor separation occurs, its like the resin will not move into these small areas and you can see a litlle of the weave. but it also maybe me contaminating it too. like others i have a single garage that doubles, no wait tripples as shaping, glassing and sanding bay. haha

does anyone else have this type of prob on fill/gloss coats?

i know i def need a more stable temp lam room.

Sounds like you’re talking about fisheyes. Usually it’s due to fingerprints or other contamination. Once it’s lammed, don’t touch it without gloves on. Scuff it with 80 grit, and a quick wipe with DNA and a CLEAN cloth. I use a heavy duty paper towel (“Shop Rags” from HD) and reuse them only to clean your tools. One for the deck, and another clean one for the bottom.

Thanks nj, i must admit i have been probably a bit casual in my handling of my boards. but having said that i hotcoat after lam when it tacks off so i dont touch it between lam and hoat coat. is it possible that i am contaminating it when im rolling out the glass and cutting it ready for the lam? i do that part with bare hands… should i use gloves at this point too?

Hey moonfish

I got the heads up from Kinetics themselves

After lam has cured enough, scrub the lam with a scotch pad and water.

This will get rid of any blush and contamitates.

Then give it a quick rough sand with 80 grit then wash off thorough and let dry.

Then do your fill coats.

Since I have been doing this method, I have never had a problem

You MUST wash before sanding.

I made the mistake once of thinking I could sand first and wash it all off together, but I ended up sanding all the blush and contaminates into the lam coat.

I ended up with fisheye all over the board.

Before I do my gloss coat, I wash the board thoroughly after sanding, then give it a good clean with “wax n grease remover”

You can buy it at any auto suppliers.

Perfect gloss coat every time.

Hope this helps