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Comparing different epoxy kits


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I'm doing some research to better understand the relevant characteristics of different epoxy resins that are available out there. I'm working off of a cozy mkiv kit, here's a quick comparison (attached). Some findings:
- I see a lot of discussion online that recommend using MGS L335 and L287 systems, but from the data it seems that these systems have considerably low glass transition temps especially if cured at room temp without extra heat treatment. I can imagine some hot summer with temps well into 100's, so that's dangerously close to L335 Tg (about 130F, room temp cure). Will probably only use what's left of my L335 resin for slurry, micro and foam work
- HTR-212 data shows numbers I like most, but no mention of the epoxy in the plans

I'd love to get the input of experienced builders, to me it seems that the HTR-212 is the best option, I don't want to deal with post curing, I want the simplest building process. If anyone know of caveats or gotcha's of using one resin vs the other, input is really appreciated


Screenshot 2024-07-01 at 2.34.15 PM.png

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I am not sure if you have seen this website. If yes, please disregard this post.



For epoxy info, have a look at





Gary Hunter is a highly regarded epoxy guru with industry experience. See his presentation (linked above) for an in-depth information on epoxy. Also, make sure the epoxies you choose are approved for cozy structural construction.

Good luck!!!

PS. Disclaimer. I did not build my current project. Bought it almost finished. So not experienced by any means of the word.

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So I asked Gary Hunter about the HTR-212 epoxy, because given the unbelievable stats shown above, I was extremely skeptical. Here was his reply (it's long):


Yeah a typical  after market supplier that buys drums of product from the big producers, like 3M, repackages it into quarts gallons, etc and quadruples the price.  

Typically, they don’t have the resources to generate their own Safety Data Sheets, so they plagerize their suppliers data sheets.  These SDSs are way out of date and probably not legal anymore.  
Part A ingredients are spot on for a tough, chemical and high heat resistant resin.  A blend of generic Bis-A epoxy, and a multifunction Novolac epoxy for the chemical and heat resistance.  Then some polysulfide epoxy for toughness. 
Part B MSDS sheets are somewhat inaccurate in identifying the actual chemical name of the components.  According to the CAS #’s the first and main ingredient is accurately described as Isophorone diamine (a cycloaliphatic diamine good for heat and chemical resistance). The second is vaguely identified as an Amine, but more accurately should be calked an “aliphatic amine” specifically triethylenetetramine (my favorite hardener I use religiously).  The 3rd and 4th ingredients are incorrectly identified as a modified aliphatic amines. The 3rd  is actually not an amine at all, but rather something called nonyl phenol (an accelerator), and the 4fh is  actually an aromatic amine called meta xylene diamine. ( also good for chemical (fuel) and heat resistance). 
But, this formulation will not develop any of those potential chemical and particularly heat resistance properties without a post cure.  They do not mention a Tg value typically measured by DSC (differential scanning calorimeter) or a thermomechanical rheometer. 
But rather they reference a heat distortion temperature, or heat deflection temperature.  Which is obtained from a mechanical 3 point flexural test immersed in an oil bath that is slowly heated.  A fixed load is applied  and when the specimen deflects 0.1 inches the temperature is recorded. This ASTM test was originally developed for thermoplastics like polystyrene, polyethylene, polypropylene and nylon.  It was later applied to thermoset systems like polyesters, epoxies and urethanes.  It was developed before the DSC and Rheometers became more common.   It provides useful data as to maximum use temperature (not a Tg) for the material.   On a pure or neat resin specimen, the HDT is about 10C higher than the Tg. 
However, some proprietors use a fiberglass or carbon fiber reinforced specimen to run this test.  After all, it is a resin system intended to make a fiber reinforced composite. As such, with a fixed load based on geometry, it can result in misleadingly high values.  This is how they claim such high numbers without a post cure. 
If you read the reviews, one user states it does need a post cure to get the high heat resistance. 
This resin system is about 2-3x the typical viscosity of most laminating systems.  As such, best results are obtained with a vacuum bag and a heated curing cycle.  Otherwise, the fiber to resin ratio will tend to run low. 
It’s a well designed formulation, but rather viscous and needs a post cure.
The Mako 305, at least, is not claiming insane #'s, although the Tg is still VERY high for a RT cure, and I'll bet a lot of $$$ requires a post cure to reach.
So, unless you're working in a heated space and are planning on vacuum bagging and post curing, those HTR HDT/strength/stiffness #'s are total BS in the context of comparing with other epoxies.
Use one of the approved epoxies, like 4000 people before you have done, and move along. MGS is good; Pro-Set is good; Aeropoxy is good; West Extra Slow is good; EZPoxy is good. Viscosity matters - lower is better for wet-out and weight. EZPoxy is the best for fuel resistance.
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