I stumbled across there website and was curious, Has anyone here used it?
Yup,
The mix ratios of the Greenroom epoxy are complicated. You have to mix both fast and slow hardeners with the resin component to dial in the curing time. There’s a chart of hardener mix ratios included with the resin. I needed a calculator to figure out the right amounts.
My first lamination with the stuff started to kick before I was done lamming and I got a big dry spot. My fault though, it was in the summer and I probably didn’t account for the increased ambient temperature to accelerate the gel time.
Finished laminating the board with Greenroom and hotcoated with Resin Reseach.
I still surf that board on occasion (with the dry /delam spot) and it works well.
Overall not a bad product, clear and strong, but I would rather stick to a simple 2:1 mix ratio though. Just my opinion.
~Brian
Brian,
The mix ratios for Greenroom epoxy are 2:1 by volume or 100:44 by weight. I highly recommend that people use a scale and measure by weight.
There are two hardeners, a FAST which almost everybody uses for laminations and hot coats and a SLOW which was designed as a low exotherm hardener for fin boxes etc.
The two hardeners are completely compatible and can be mixed as you said to dial in gel times. (EDIT ADD: the mixing of fast and slow hardeners is only for convenience to make gel times to your personal preference, HOWEVER most people use the FAST only for laminations and hot coats. The FAST gives a 15-20 minute gel time @ 77°F)
For example, with a 100 grams of resin, you would use 44 grams of FAST hardener for a quick gel OR 44 grams of SLOW for a slow set.
To get an intermediate gel time with a 100 grams of resin you would add 22 grams of FAST AND 22 grams of SLOW. Notice that the total amount of hardener still adds up to the 100:44 ratio (22 fast + 22 slow).
Here is the simplest way to ensure perfect ratios every time when using a scale. First get a scale and then tape a $1 calculator (I like the one with big buttons from office depot) to the wall next to the scale.
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put your empty container on the scale and tare the scale. the reading will be 0
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pour in your resin and take the the weight and enter into calculator. Say in this example it is 250 grams of resin.
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multiply your resin weight by 0.44 so, 250 x 0.44 = 110 grams
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without removing your resin container, tare your scale again. reading goes back to 0
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add amount of hardener from calculator…in this case 110 grams.
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mix well and a you get a perfect batch.
If you have any questions, feel free to email or PM me.
Rob
I have made 3 boards with it so far. The resin is fantastic. No additive F to mess with. sands great.
The BIGGEST advantage to me have been that it mixes up clear and bubble free.
I had a lot of problems with froth and bubbles with the Resin Research epoxy.
Getting near perfect bubble free gloss coats now with GR epoxy. Latest one had just a few dust specks in it.
Recently made an 11 ft board in 95 degree heat. No problems with wetting out the cloth in time. I did the lam coats in 2 steps. First mixed just enough to do the top . then a second batch to tuck the rails. I think I will do all my longboards like that now.
Been using the fast hardner so far but next time plan to get some slow for one step exotherm free finbox installations.
Staff at Greenroom has been very good at answering any questions I have had about using the resin. Michael
Hey Rob,
Don’t get me wrong, Greenroom Epoxy IS a good product.
I just posted my experience with it from 2 years ago. The fast hardener kicked much faster than the 20 minutes listed on the mixing sheet, not to say any other epoxy system wouldn’t do the same thing in the same conditions.
Since the instruction sheet advises not to use slow hardener (gel time approx. 160 mins) for laminations since “significant drainage off the rails will occur” I needed to mix some fast harderner in to get the working time up. So essentially you need to have both harderners on hand to lam in higher temps. I guess there might be advantages to adjusting working times in certain situations…
Again, good product, keep up the good work!
~Brian
Hey Brian,
I like to get real world input, so thanks for your post. We are proud of our current products, but are always working to improve things based on user input.
I just wanted people to be sure and understand that GR epoxy is a 2:1 by volume ratio mix.
I tried to design the system where people could dial in their gel times to their specific needs. I can easily make a medium speed hardener, but have not had many people ask for one.
Speaking of gel times (and how they do or don’t relate to actually building surfboards), the industry standard for measuring gel times is in 100 gram mixed batch in a cup at room temperature (ie 77°F). This is how we measured gel time for our tech sheets. Gel times are a function of cure rates, but cure rates are also a function of the mass (how much) and area that mass is spread over. (From an earlier post of mine) For example, you cannot compare the cure rate of a 100 g epoxy mix in a cup to the cure rate of that same 100 g spread into a thin film. Anybody who has left a large epoxy batch in the cup can attest to this as the exotherm in sufficient mass can be compared to a self-fulfilling apocalyptic prophecy!
So if you are comparing the same mass to area ratio, then the general rule of thumb is doubling of reaction speed (cure rate) for every 10ºC (18°F) for most room temperature curing epoxy, but that is a very general rule and doesn’t take the heat generated by the exotherm into account. 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) and GR does not exactly follow the general rule of thumb. Nevertheless, what that means for board building is what everyone knows, when it’s hotter the epoxy will kick faster. So, with our FAST hardener gel times vary from ~35 minutes @ 60°F to ~12 minutes @ 95°F. But again, these values can and will vary considerably with the mass/area ratio changes from the standard method of testing.
Wow, I sound like a geek.
Rob
Thank you all for the info, i will be trying it on my next batch of boards.
Hey Rob,
Thanks for the geeky wisdom 
I can definitley see how the exotherm of potted resin makes the cure non-linear, especially when you have a larger mass of mixed epoxy. Makes a lot of sense.
Take it easy,
Brian