Best epoxy hardening temps?


Had a quik search on the archives to no avail.  I have heard a few different points of view of what is the best temperture for epoxy resin to set at.  Some say a long cool cure will be stronger so it can form a better structure, or is just for Poly resin?, some say always glass in a dropping temperature,  or some people bake it at high temperature for a few hours.  If so im thinking I could park my car in the sun with the heaters on and lay the bard in there to harden? Is this a good idea? Someone set me straight.

Also how does it differ from Poly resin. Cheers

Is there a better way of doing this and anyone know where to get paint filter paper as suggested on here?.  B&Q and Homebase had never heard of 'em.


Answer:  Yes just filter it through a layer of 4 oz cloth, that works just fine.  If you really want the paper paint filters....guess what...go to a paint store.  You do have paint stores there in Fogland?

epoxy is best used when it around 73 degrees. It can be used in the mid 65, but not recommended to be lower than that. The reason is that it will take a long time to cure/ kick.  Cold epoxy on clod wet days is a recipe for disaster.  yeah, yeah you can heat the room, put a dryer in this or that. but net/net warm days are best.


The deal with a droping temp is for the EPS foam.  Cooling EPS foam will suck in air. Heating up EPS will expell air. So if you glass / hotcoat on a rising temp, be prepared for a gassing farting blank...meaning volcanoes in your epoxy.


Epoxy cures with heat, I've never heard of a long cold epoxy cure.  Yes epoxy gets harder over time, but only to a point.  To post cure you can put your board in a semi hot car all day.  Semi hot meaning 120-130 degrees. Not a 200 degree car. That will give a pretty good post cure. Or you can build a post cure box...or you can just forget about the post cure, make sure you mix the epoxy right on a nice sunny day, and be done with it.


The most important thing with epoxy is mixing it right and accurately.  Take the time to mix it by volume, not weight. And make sure you mix it throughly...don't whip it to a froth, but mix it deliberately and throughly. Epoxy has a nice long pot life. you can mix for 2 minutes, scraping the sides and making sure the bottom muck is mixed with theo top muck.  If you mix properly you won't have 99% of the problems the smucks post here who say "gee my epoxy doesn't want to kick", or gee it's been 3 weeks, why doesn't my epoxy kick"........well it always gets back to screwing up one of the steps above.

Epoxy vs Poly.

One eats EPS foam the other doesn't.  One smell, the other doesn't.  One kicks fast, one doesn't


Use Epoxy for a blank of EPS. All there blanks use poly resin.


poly resin makes a cosmetically superior board.  Eopxy is more resilient and makes a more ding resistant board.  But that all depends on what kind of glass you use.


Ok enough with you...go make a surfboard and report back.

Ok great, thanks for all the info.  So im thinking I might try the post cure trick in my car to make sure it gets good and hard before it gets cold at night.  But I shouldn't put it in till its kicked, or maybe the de day after laminating?

Sorry I meant how does poly differ in terms of best temparature.  Is hot and dry always better or does long cold cure apply for poly only?

I agree with Resinhead. Keep in mind you are building a surfboard not a spaceship. It's a proven fact that a proper post cure will yeild a better product. How anyone can get a proper post cure in their car is beyond me. I've even read that a post cure done wrong will yeild a weaker product. Glass the surfboard at 70-75F. Do all the lam and hot coat in less than 24 hours. Let the board sit inside the house for a few days before you sand it....and...sanding makes heat. Overheat the board while sanding and you wasted your time post curing.

That's my opinion



You're getting solid advice/info from guys who actually have enough experience to hand it out.

You should always follow the guidelines of the manufacturer of your resin system. They are going to know their product best. We use RR, because it is a surfboard-specific product that has 30 years of development. Greg Loehr also has an intimate knowledge of his product and has user info right on his website for people new to the resin. Hopefully you're using his resin or a company that has similar support/info for the customer. We like to have at least 70F temps, both ambient and resin, for our process using RR.

Re the differences between epoxy and polyester: Epoxy is an ''additive'' reaction, the two parts combine; as opposed to PE, where a catalyst initiates the linkage of polymer chains but doesn't become part of the chains. Much higher VOC emissions with PE, much better physical properties with epoxy. Epoxy is also lighter than PE but still has a higher solids content.

Almost all epoxies will benefit from heat and pressure while curing, but you have to consider the whole composite. Polystyrene cores won't tolerate extremely high temps, so 120-130F is about as far as you want to take them for your first time post-curing.

...if you're going to throw the board in the car with heaters to cure, do it before you hotcoat... I built a Hot Box to make the epoxy kick quicker and I found, exactly like Resin Head said, you pet pinholes in your glass.  I also found that it melted all the wax in my additive F and the board was harder to sand. 

I do like to cure the boards in higher temps, not just for speed, but Epoxy  has  a memory, and if you cure it at 120 degrees, it will have to reach 120 degrees in that car of yours before it begins to fail.  Also, the boards tend to be significantly lighter when I glass  in warm conditions.

So there are different temps for the different steps..

I vacuum bag boards ideally around 70, so the resin has time to be absorbed into the breather.  I let that go for a couple hours with the vac on, then throw it in my HotBox and get it up to around 120 for high temp cure.  Pull it out, while its still warm and hotcoat it with epoxy in room temp, so the blank wicks the resin in.  (microwave your resin for the hotcoat and leave a fan on the board while it cures for best results..)

good luck

you dont need to post cure

just do it on a nice day, after 1 pm, as the temps drop

it will be cured in 2 to 3 hrs

and mix the shit good

like mr resinhead said

purely by the feel of your story i am asking for some pics of your boards

it sounds like they are great!


See if you can read a little about Resin Research Kwik Kick. You can get it from Seabase in the UK. 

It makes a lot of the old information on Swaylocks out of date. It does go off faster (similar to PE, but if your laminating in under 75 degrees then you have plenty of time.

Warm a room or small space up to say 75 degrees and then move the board in there and it will go off in an hour or two.

It also won't stink you out.


Health and Safety: Nitrile disposable golves and you probably still need a respirator because of the additive F. Especially in a confined space. You add a small amount of Additive F for lamination and a bit more for hot coat as it makes sanding easy.

There are full instructions over at foamez.


 Not really answering your question, just putting it out there.

20 degrees celsius is what I would call minium temperature for working with epoxy otherwise it gets too thick. 25 degrees is even better. As claude said epoxy wont stink the place out and I find epoxy more ding resistant than polyester on a PU foam board. Also check out this thread.

I just hit a fill coat with RR CE (Fast hardner) at 76 degrees - looks pretty good at this point. :wink:

Did a lam 2x4 oz S glass + deck patch the other day at 85 degrees and used RR CE with the slow hardner - worked great. :wink:


But - I make 3 boards / year…

Cheers everyone.  This seems like a lot of good sound advice.  The first lam on new board had gone alright. 

One thing im worried about is that my add f always gets cold at night, even in the house, and solidifies. I shake it for ages and warm in up but I think this is still causing precipitated bits when added to the resin that I blame for loads of craters in the hot coats in the past.  Will a long soak in a water bath remedy the situation? or any other bright ideas?

Thanks again.  

...The Add F...yes...the Add F.....

If you have a shop temp of 75F...and your blank has a temp of 75F...and your chemicals have a temp of 75F....

your ADD F will be 100% clear and ready to go !!!! and your surfboard will cure just fine in a few days with no postcure.

But.............It's cold where you live and my methods will not work for you. Please read this thread...



And One More Thing...

All that new stuff from Resin Research...great stuff....same rules....Kwick Kick or CE or the old stuff....

proper temp...measure good...mix good.....Proper Temp....Measure good...mix good....


Aaagh.  Nightmare with the hot coat.  Thought I did every this right this time.  Using RR KK, 25C / 77F, heated add F in water bath, waited an hour for the lam to gel, didnt touch it, and slapped 225g of resin on with 2% add F. 

This ALWAYS happens.  WHY?

howdy nick

it is very annoying indeed to see those fish eye pop up

one thing we can check is if you used a new and clean mixing bucket?

is it a mixing bucket for epoxy, or just some empty mcdonalds 1 litrecola tray?

and how about the brush, was it new and clean? is it a brush for poxy?

and what do you consider clean? i dont mean clean as in cleaned eh!

did you use add-F in the lamination stage? it prevents fish eyes.

if you really want to find out, you could even start telling us about the room you laminate in, room temperatures, humidity percentages of the air...

did you use a compressor to blow off the board before hotcoating?

well, let us know and it might be solved for the 2nd hotcoat this board is going to get!


That my friend is contamination. What did you wipe the board with?  What brand of hand lotion did you have on your hands when you picked up the board?  Have you been working on your car simultaniously while glassing?  Were you spraying anything around your board before you hotcoated?   Something like silicone spray, WD-40 etc?

Here the advice to never, ever , ever have this happen. Take it word for word.   Nothing will be cleaner than a freshly sanded board. Nothing will be cleaner than a freshly laminated board.  Everytime you touch it, wipe it ,fondle it, rub it, etc it gets crap on it that can cause this kind of a mess.

There was an outside chance that something was in the epoxy on the lam, or in the bucket you mixed....but then I refer back to the clean room treatment.

I wash my hands with soap, I dry them with paper towels. I don't ware any brand of gloves that I don't know.  I never let people touch a freshly sanded, laminated, or shaped board.......they can touch it when it's done. I use disposable cups to mix, I never recycle stir sticks.  I'm pretty much a Howard Hughes freak about this shit............and guess what. I never have any fish eye problems...or in your case the topo of the moon.

sand it down as best as possible....bring it too the lam, you'll be suprised how good it will come out.  If you got some patches where it needs to be touched just that, paint a little expox on and resand.

What a mess.

Ok.  I defo didnt touch it, hot coated when the lam was still sticky and havnt been spraying and grease or anything. 

I am thinking about the mixing pots.  I reuse yoghurt pots that are pretty thourerly washed out with the washing up and rinsed.  Possibly a tiny residue of the washing liquid? 

Used a decent spanking new brush without colored bristles.

Been doing it in my outside shed, a good 25C afternnoon and hasnt rained for a couple of days.

There is still quite a bit of eps and wood dust kicking about that I missed with the hoover.  But why would dust make the resin reppel the lam.

The neighbors aren't going to appreciate the sound of the inpending sanding session...