FW: [Canard Forum] Epoxy
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This came across the transom on the Carnard Forum, and I thought it was worth posting to the Q-list as well. Probably good information from an informed source for all of you who are new builders or are still building/repairing.
Mike B. and Charlie J. you guys probably have valuable comments on the material in this note.
Merry Christmas to you all. (I went flying this morning, but had to get down before the airspace filled up with flying reindeer and sleighs!)
From: mailer@... <mailer@...> On Behalf Of Gary A Hunter (gluegaru@...)
Sent: Saturday, December 24, 2022 1:10 PM
To: Canard Forum <forum@...>
Subject: [Canard Forum] Epoxy
My apologies for the slow reply. Wrapping Christmas gifts takes a lot more time these days.
Poly Epoxy is not one of the recommendations for building the VE or LongEz, but that is mainly because it is a rather late entry into the market and the viscosity is bit high. However..
The maker of Poly Epoxy is System Three, that was a customer of mine back in the days I worked for Shell’s Epoxy Resin group. They are a very good formulator in my opinion and know what they are doing. I looked at the Safety Data Sheets for the the product to see what the basic formulation is comprised of and it seems to be a well thought out system. Much like EZ-Poxy, the curing mechanism is based on an aromatic amine, and modified aliphatic amine, which is by far the best you can have with regard to chemical, or fuel resistance in our case. Unfortunately, as like many, they don’t report any relevant chemical resistance data other than moisture uptake. The mixed viscosity is definitely on the high side compared to most other systems. But, it should be OK if you pay strict attention to shop temperature control. I would say nothing less than 75F. But, with you being in Chicago, that could be a problem for you. The reported mechanical properties of the cured system seems to be in line with comparable recommended systems such as EZ-Poxy, Pro-set and Aeropoxy. And, as always with any system, I highly recommend a post cure to obtain that little extra chemical and heat resistance.
Although, quite a few people have used the MGS systems, it is not one of my favorite systems of choice. Particularly because of the curing agent chemistry is not renown for basic chemical resistance, especially MOGAS. The reason most people like the MGS system is the extremely low viscosity, and the fact they offer slow and fast hardeners to allow one to tailor the formulation their specific application by blending. If one uses this system, post curing is a MUST. It is very expensive, and sometimes hard to get because the components are made in the USA, shipped to Germany, and back to the USA. Technical help is good, if and when you can find it.
Pro-set is formulated by the same people that formulate West System for marine or non-structural applications (Gougeon Brothers, Midland Michigan) As such, their technical support is reported to be top notch. They have been around a VERY long time, and they were my customer for epoxy resins when I worked for DOW Epoxy Resins. I’m retired now. They definitely have skilled chemists and formulators and testing capability. A bit more expensive than Poly Epoxy, but many more options available. Their LAM-125/LAM-225 (medium speed) system, is what I would recommend. Their fast hardener, LAM-224 is excellent for small jobs like tabbing and bonding components together. They all have the same 3 to 1 by volume mix ratio, so making blends of LAM-225 and LAM-224 can be make to adjust cure speeds. Their technical data is excellent too. And of course, you will see they recommend a post cure to obtain optimum properties. It’s not a must, but highly recommended. https://www.prosetepoxy.com/standard-products/laminating-epoxies/
I know that you mentioned that Poly Epoxy is stocked in Aircraft Spruce’s Chicago location. I can see how that would be plus with regard to shipping charges. You can simply drive over and pick up more resin as you need it. But I wouldn’t make this a driving force on your decision towards which resin to use. By purchasing larger quantities of an alternate system not stocked in Chicago, you can save money and reduce hazardous chemical shipping costs. And you will get a more user friendly resin system. What about shelf life you ask?
Pro-set posts a 3 year shelf life the resin and 2 years on the hardener. This is simply to limit their liability and comply with certain government contracts. But, I can tell you for a fact, they are much more longer than that. Basically, forever - if you store them correctly. Don’t worry too much about the epoxy. It may crystalize, as the data sheet says, but it can be reconstituted. But, the hardener benefits greatly by being stored in a tightly sealed container - glass is best and with an inert head space. i.e., Nitrogen, or argon if you have a welding unit. So, if you buy a 5 gallon container of Hardener, you can break in down into 1 gallon glass wine jugs, or quarts - and just prior to putting the cap on, purge the remaining space between the liquid and the opening of the container with nitrogen or argon, and quickly put the cap on and tighten. Tape the cap in place with electrical tape. UV light will cause the hardener to darken, but will not affect the chemical composition or stability. But, to avoid that, wrap the container with aluminum foil, or simply place the containers in a dark cabinet. Repurposing, quart or gallon Paint Thinner cans is another option if glass doesn’t appeal to you. Plastic containers present a host issues over long periods of time. I would avoid them.
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