epoxy board cure time

I’ll respond in generalities and not compare any products on the market, use the information as you see fit. For cure rates, you have to compare apples to apples. By that I mean cure rates are also a function of the mass AND area that mass is spread over. For example, you cannot compare the cure rate of a 100 g epoxy mixed and left in a cup to the cure rate of that same 100 g mixed and then spread into a thin film over a large area. Basically, the reaction in the cup creates heat through the exotherm which increases the rate of reaction which increases the exotherm….so and so forth whereas the same amount of epoxy spread over a large area will let the exotherm heat dissipate and the “cure” will be slower. Anybody who has left a large epoxy batch in the cup can attest to this as the exotherm in sufficient mass is a self-fulfilling apocalyptic prophecy!

So if you are comparing the same mass to area ratio (such as laminating the bottom of a board with a normal amount of epoxy), then the general rule of thumb is doubling of reaction speed for every 18ºF (10°C) for most room temperature curing epoxy. So, say your epoxy cures in 2 hours at 70°F, then it should cure in 1 hour at 88°F and 30 minutes at 106°F. In fact the relationship of cure speed with temperature is non-linear (it really approximates an negative exponential… look up the Arrhenius equation if you’re sufficiently geeky). Actually, it is a little more complicated with resins because their viscosity also changes with temperature and that has its own effect on reaction rates. That is why almost all epoxies, except very specialized formulas, will not fully cure below a certain temperature…the rate of reaction slows to almost nothing due to the temperature decrease and viscosity increase. Here the general rule of thumb is that temps. must be warmer than 50-60ºF depending on the specific epoxy. BTW, letting the mix warm up some in the cup is serves exactly the same purpose (except for the ease of mixing) as microwaving the resin. Sometimes knowing how long to let the mix warm in the cup before throwing down a hot coat is the difference between glass smooth and orange peel, but that is where experience really comes into play.

This also has a bearing on post cures. At any constant temperature (this could be the case in a lamination or hotcoat where the exotherm heat is dissipated), as the reaction continues the rate slows down. In simplest terms, the two reactive molecules (resin side and hardener side) have a harder and harder time finding each other because there are less and less of them left unreacted and they are being trapped in place by the transition from liquid to solid. Some resin systems will never fully cure past the Bstage without the addition of heat more than room temp (think about pre-pregs) and even some room temp cure systems will not reach full cure at lower temperatures. Post-cure heat helps to “re-liquidfy” things and the remaining reactive molecules can now find each other easier. Ideally, post cure heat should be applied in the Bstage before the reaction has gone too far because after a certain length of time the cross link density is too high to allow much movement without a tremendous amount of heat. Nevertheless, a post cure especially at a temperature above the resin’s Tg (glass transition temperature is where the polymer goes kind of rubbery and is usually something around 130-150ºF for most room temp cure formulas) will do some good. The problem with surfboards is that high of temp can start to affect foam stability and cause out gassing. I would say most surfboard builders never reach a true post-cure temperature, but rather more accurately an elevated temperature cure which still has benefits of “loosening” things up to reach full cure faster. Bottom line is that all epoxies love some heat and it plays a much bigger role for epoxies than in polyester resin which reacts by an entirely different mechanism. Real world conditions are often not ideal…get to know how the products work under the conditions you normally work in… Charlie is right on target in this regard.

Even though I am pretty sure I never answered the original question, I hope this helps anyway. I wish I was back on Oahu to discuss this over a beer with you. I find beer is like a post cure for my brain….helps to loosen things up…and just like post curing there is such a thing as too much of a good thing.

Rob

For everysurfer: temperature cycling promotes crystallization of epoxy resins…just as you described.

RobW, Very good information. Thanks.

Dwight,

  so you lam both sides and filler coat both sides and get it in the oven in one day????  If the spec GR flip times are say 2.5hours . So it would be about 8-10 hours until you were getting the last side with the filler coat and putting it in the oven still wet????

 

Also, when you put a final coat of epoxy for a polished board are you baking that final coat also?

 

The smell I am thinking of is about a two minute warning to get what resin you need on the board. Hoefully nothing will be left in your bucket to exotherm.

I live in a consistantly warm and arid climate. I microwave aluzine resin for my final coat to get a water like consistancy. Usually never more than 10 ounces in a red solocup with the white inside.

Green room resin is water like consistancy right out of the bucket. I like that part about it.

I don’t notice any smell when sanding epoxy. Even the 4:1 ratio I used in the 80’s.  I use a router to take off my excess pre glass box/leash plug installs to totally remove the sander heat build up on those areas.

I guess if you had to warm up large volumes of epoxy, you need to consider a 8 person jacuzzi and keep a gallon in there when needed. Check with your accountant. It should be a write off for you.

For Fiberglass Hawaii epoxy, do you use the “thick and fast” and heat it to thin, or the “fast”

Rob,

 Thanks for the detailed response and customer support you provide for your epoxy system. I see some potential advantages of of the GR already. 

 

My question still goes back to the oringal poster’s concern.  For me I would not hesitate to use an epoxy surfboard that has been lamed, filler coated, sanded, final coated and polished with no 100 degrees for 24 hours curing anywhere in the process.

I have been know to throw a board in my SUV to bake it so I could sand it sooner. But with the newest reformulated epoxies and surfacing agents I don’t even do that any more.

Now that I have been thinking about this more and reading your post I am even a bit more confused.

Dwight’s “shame on you” for not post curing comment really seems like manufacturer hype now. Since you post cure after the filler coat, unless you post cure each side seperately, you would loose the ability to maxiimize the post cure effect because one side of the board will have cured longer at a lower temp than the other when finally put in the oven. Also, do you calculate if the deck or bottom needs the maximized effect of the cure and glass appropriately? Many backyarders, including me, have to put a half made board away for a week.  I still am leaning towards the idea that the post cure efffect has little if any real world signifigance with surfboard durability. 

If I had a facility that post cured  boards  I certainly would be shouting it from the rooftops as a benefit and use it as a selling point. The benefits I could actually claim though would be…never breaking board???  Stronger/lighter???  Good foam, good glass job will give it durabilty.  If the crutch of the maximum effectiveness for a superior product with an epoxy system is post curing, that would be a hard sell to the probably 90 percent of epoxy board builders who do not oven cure.

I can only conclude that post curing is nice but certainly not a necessity for a strong/light durable epoxy surfboard. I see the usefullness for making a better product to sand for the sander with an overnight bake though.

aloha,

Charlie

 

ES,

I use the part A aluzine resin and heat in the microwave. I add my part B fast hardener and stir then my additive F or equivalent.

I am not sure what you mean by "thick and fast" or "fast"(unless you have been talking to my wife)

Sounds like there is a new product out I am not familar with at FGH

aloha,

Charlie

They make a “Thick and Fast” for hot coats.  The label says Fast on the top, and then in a white box it says “Thick and Fast”.  Then they also have a hardener that just says “Fast”  It is thin like their slow hardener.  It might be new.  The first time I saw it was last month.

Even old dogs learn new tricks.

Where do you work?

I used to post cure or whatever you want to call elevating the temperature during the epoxy curing process. Multiple boards at a time… Definitely feels a bit more solid to the touch. However, I no longer post cure because I feel the extra energy involved in heat (at least electric) is not worth the result. Epoxy is strong enough for surfboards without postcuring. If you’re hitting a board hard enough to ding epoxy, it’s gonna need some repairing postcured or not.

Old Post cure box

Also, wait about 2 days after hotcoating a board with epoxy then sand. The cure slowly ‘creeps’ to a point where the hardness is high enough for the sandpaper grit to cut it clean.

But, you can sand an epoxy hoatcoat shortly after is has initially cured with fair results, it’s just different than waiting a couple days.

~Brian

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I know this topic has been kicked around, but always having to do with questions regarding what type of epoxy, post-curing rates, and glassing.  I just picked up an epoxy board that was glassed a few days ago, sanded finish.  How long should I wait with the board in a garage at 70+ degrees before I should ride it?  Any data on this?  Thanks for any info.

[/quote]

 

Hello Ron....your board is already post cured and ready to ride...post...aka after....get it? The board continued to cure after it was glassed. I own the Low Tech Lab. Don't be fooled by internet posters. The shaper / glasser would not have delivered the board if it was not ready to surf.

Stingray

There is some great first hand info on this thread. First, let me say that I tend to agree with Charlie in that “post cures” are not essential for a well formulated room temp cure epoxy. This is especially true for an environment like his that really hits the sweet spot of curing temp and stays there day and night. For other shops, where temps may routinely drop in the 60s or even 50s for extended periods, the benefits or even necessity of an elevated cure temp become more apparent. The goal of a formulator of room temp cure systems is to produce a system that will achieve its maximum properties (or at least very close to max props) at room temp and most everbody defines room temp as 75-80F. Many of the products that are on the market today do an admirable job of achieving this goal. What many people don’t realize is just how good surfboard epoxies actually are. They are on par and in many cases better than products used in aerospace and military applications.

With all that being said, there are some measurable properties that all improve with even a moderately elevated (100 - 130F) temperature cure schedule (at least for the systems I have tested). The most important for surfboards is an increase in the heat deflection temperature, increase in % elongation and increase in hardness (barcol or shore D). These are all positives and the degree by which they improve depends on the specific formulation, but they all improve somewhat. The question is whether the extra effort is worth it. Well, some of the benefits are less likely to warp inside a hot car (higher HDT), less likely to suffer shatter dings form car doors etc (more elongation) and easier sanding (hardness). In addition, most all formulas show better color stability (less yellowing). So from a durability and cosmetic aspect, post cures do good things. What it means as far as resistance to snappage and the always elusive “flex” properties…well that’s for the marketing gurus to spin as I haven’t found a good way to quanitify those properties yet. And I think that marketing a surfboard as unsnappable (I’m not sure that is a real word…maybe marketing is in my future) is probably not the way to go anyway.

Many people have asked how long can you wait before you post cure. There is no set answer for this because it depends on the cure history before the post cure. If you laminated and have the board continually at say 80F, then you probably have around a 24 to 48 hour window to get maximum benefit, but if (god forbid) you lam and hold the board at 50F, then you probably have at least a 3 to 5 day window and possibly longer. Another thing that is generally advisable (although with only moderate temp isn’t essential) is that you should ramp up to your post cure temp rather than throw the board directly into the pre-heated room.

If you are happy with your boards without post cure, great you are just reaping the benefits of modern chemistry, but if you have the means to post cure without too much added effort, I would and do.

Rob

Charlie, I love that response about your wife.

When I did boards at Dad’s house in the garage, it would get damn hot. I’d say in the high 80’s or low 90’s. Helped that Bernie and I would tag team it and do one side each. When we took boards out in the sun after we did the fill coat or when we did the final coat, the resin would start to bubble. I have a couple of boards with tiny bubbles in the final coat, lots and lots of bubbles. PU cores with wood veneer.

Great advice Rob,

Just got an email from the GR  distributor here and they say I have the “original fast” and there is a “WC Fast”(1 gallon) avialable. Can you explain the difference??

 I just did my deck gloss final coat and it is looking sweet. Took 8 ounces of GR resin and heated it to 120 degrees F and added 4 oz of room temp original fast and a splash of xylene/parrafin surfacing agent. Removed tape at 1 hour and it was on the uncured side of tacky. The cool thing about exposed cork decks is you can flip to bottom up and gloss final coat after you blade off the resin line from the tape off on the rails. This would occur at 40 minutes with aluzine. At two hours post application of heated, origianl fast, the GR epoxy is still too tacky to blade and tape off for the bottom to be done.

Is it at all possible that I have slow cure that is mislabeled?? Slow aluzine would be ready to go in 90 minutes. I have had a problem in year 2000 with RR and the local distributor took it back and said I was crazy. In 2002 I was sold 5 gallons of aluzine fast labeled in a slow container. I started using it and realized I could do most of my work with fast.

I so want this product to work for me for many reasons.  But after hearing that most GR users in hawaii use medium cure I am totally baffled using the original fast.

 

Harry,

 Since I made some boards with you in 2003-2005, the resins have been reformulated. I also soap and water wash boards prior to gloss/final coat with great results.

Fill coat bubbles  really don’t happen that much with the new resins. The GR was great in regards to this with 42’ feet of filler coat done so far.

 

Thanks for this Post Rob… Lot’s of good stuff in there.

I would wait at least a week from the time the final sanding was done.  Keep in mind that the heat from sanding and polishing contributes to the curing.  Post cure that I recommended is done when the hotcoat/fillercoat is not sticky to the touch.  It doesn’t have to be anything fancy, any small room with a 800w ceramic heater works and it doesn’t take long to attain 100F.  Get a non-contact thermometer and check the surface temp of the board to work out the timing of the heater.  If you have the space, just enclose a horizontal wall rack with Home Depot insulation panels and put the heater in there (like the Greenlight photo).  In very small enclosures run the heater at fan only for a while once the temperature is reached to eliminate hot spots.  I must agree with the others that boards cured for a couple of weeks at normal temps aren’t drastically reduced in strength from those which are post cured 24 hrs.  However, in a production environment post cure makes sense to shorten your overall cycle time to deliver a product without any concern of when it may be used.  Personally, I’d post cure only for the improved sanding anyhow.

Charlie,

Reading all these replies is helping me understand why my methods are working for me.

My methods.

I build only in the Fall and Winter. I start a board when I know temps will max out in the 70s. Dipping into the 50s or 60s at night and early evening. I use space heaters in the garage when needed to keep temps near 70.

I built twelve 14 ft race SUPs before I ever built a single normal board. I learned building 14 footers! All were slightly flexy in the skin for a least a week after building. They were all vacuum bagged. They sanded fine, or so I thought.

When I starting building smaller boards, I was thrilled to finally be able to try post curing. The boards skins were rock hard after curing and I could sand an entire board with only one or two sheets of sandpaper. I had finally experienced the beauty of post curing, for my environment.

My timing runs like this.

Lam bottom at 6am before going to work.

Lam top at 5 pm when I get home from work.

Hot-fill coat bottom at 9pm, before I go to bed.

Hot-fill coat deck at 6am the next morning.

Place in laundry room for post cure when I get home at 5pm.

 

My hot-fill coat is probably different than most. Here is why…

I wet my cloth on a table, then transfer to the board. Cloth is rolled on PVC pipe for the transfer. This allows me to get my coth/resin ratio near pre-preg levels. I wet over black blastic sheet, so I can see the wetness better. My cloth is very dry. My boards come out much lighter than boards built the traditional way. Even when I don’t vacuum bag. I have stopped bagging recently.

Where this messes with the hot-fill coat, is all that dry cloth needs a lot of filling. So I fill coat with a squeegee, then immediately go over the board again with a brush applied hot coat. When I try to hot-fill coat in one step, I end up with weave showing. It may sound weird, but the boards come out crazy light and no dings. In fact, my boards have one extra layer of glass compared to boards built at the local factory and I’m still much lighter.

I credit this guy (Pat) with helping me understand the value of wetting on a table. http://www.lmshape.com/about.html

 

 

 

 

 

Check out the Nelson composite videos from maui. Having the space for a huge wet out table is great.

When I vacuum bag I do my pull in my hot house for 90-120 minutes to get quicker turn over times. temp is 100 to 110 if I time it correctly.

Seems like you have a great system to get the job done.

Thirty days.  Sleep with it. Hang it up. Look at it.  Touch it.  STAY OFF IT if you want it to last!

 

This thread alone has cured my recent avoidance of Sways (pun intended). And Charlie’s aloha spirit shared through some PMs…simply amazing. I look forward to meeting you in person Charlie.

Rob