Ah yes. Appears to be N357FR. I dunno about the vinyl ester. Here is a post from Gary Hunter--usually our go-to guy for anything-epoxy. Bottom line seems to say stick to the recommended building epoxies.
Having worked in the epoxy AND vinyl ester industry for over 32 years now... I feel I am qualified to do so.
Many of you have read my inputs to the group over the years. One thing you should remember is how adamant I have been about a "POST CURE". i.e., a secondary curing step using elevated temperatures to promote complete cross - linking.
Epoxy resins will not cure completely on their own under ambient temperature conditions. Once the polymer network gets to a certain point, the cross-linking slows dramatically - almost a complete stop. Over the next couple years as the project or flying article goes through seasonal and regional temperature fluctuations, it will creep along and cure a little more. Basically, these temperature fluctuations are POST CURING the laminates. But, it will never EVER completely cross link, even under these type temperature conditions. From a mechanical properties perspective, the polymer is plenty strong. But, from a chemical resistance stand point, it has vulnerabilities.
Epoxies are used to manufacture chemical resistant fiberglass pipes, tanks and structures every single day. The most chemical resistant formulations used in the industry are cured with AROMATIC amines. And, every single article is heat cured and/or POST CURED. Believe you me... if they could get away without heat curing - they would. Nuff said?
Vinyl esters are used to manufacture these same articles, but most importantly, they are used to make underground storage tanks for gasohol - which is probably why we are interested in using vinyl esters for our fuel tanks. Many of these articles, do NOT receive a Post Cure, and perform as good as or better than a post cured epoxy. WHY?
Vinyl esters cure under a different mechanism. A free radical cure mechanism - will develop a much more complete cure without a Post Cure than will an epoxy for a couple reasons. First, it is a very fast reaction, as noted earlier. And as such, it generates quite a bit of heat in the process. Depending on how thick the laminate is, the heat build up in the laminate from the exotherm can be quite dramatic - and provides a POST CURE effect. In fact, the exotherm can be quite problematic in some cases. But, as noted earlier - the free radical cure mechanism is inhibited in the presence of oxygen - i.e. it is anaerobic. This is why there is almost always a sticky or soft surface on cured vinyl ester laminates that are exposed to the air during cure. Even though this under-cured layer is only 2-3 miles thick, it is NOT going to provide the same degree of chemical resistance. If your laminate or coating is only 10 mils thick, your are in trouble.
Most important to understand, underground storage tanks for gasohol do not have to deal with this issue because they are built from the inside out. i.e., the surface that is going to be exposed to the gasohol, is the surface next to the mold surface. So, there cannot be any air inhibition of cure.
However, the FRP tank "LINING" industry is more relevant to our situation because the final layer is exposed to chemicals. However, there are some important things to know. There is no reason to line a steel tank for resistance to gasohol. And, the chemical resistant FRP industry, in general, uses a special surfacing veil on the exposed surfaces. This surfacing veil can be a special "C" glass or a synthetic material called "Nexus". These veils are ~ 10 mils thick. The area weight of the veil is such that when saturated with resin, the layer will be about 10% reinforcement, and 90% resin. This 10 mil thick surface layer provides a RESIN RICH layer that will cure more completely, and provide a more resistant surface layer. Plus, these laminates are usually a minimum of 1/8" - 1/4" thick. As such, they generate quite a bit of exotherm heat energy to Post Cure the laminate somewhat.
Now, if your are using a vinyl ester to make a 1, 2 or even 3 layer laminate to line your fuel tanks, chances are, these laminates are way under-cured for at least two reasons. #1 - the laminate was too thin to develop any exotherm energy to promote a post cure effect (a post cure would fix this). #2 - the inhibition of cure due to the presence of oxygen and your laminate is too thin. # 3 - Chances are you are not using any kind of surfacing veil. This, I believe is the reason gasohol is destroying these vinyl ester laminates in our fuel tanks.
To combat this "air inhibition", the FRP industry at one time, used a special polyester or vinyl ester resin formulation that contains a small amount of "paraffin wax" dissolved into the resin. As the resin cures, the paraffin wax will phase separate and migrate to the surface forming a thin barrier film to the oxygen. However, I don't believe this is being practiced any more. The wax reduced the chemical resistance of the entire laminate and obtaining secondary bonds to this "waxy" laminate was impossible. This caused a lot of problems in the marine industry, but makes for nice artificial reef.
So.... We are fortunate that EZ Poxy is in fact cured with an AROMATIC amine. And as such, has the potential to be THE most chemical resistant epoxy available to home builders. In the past, without a post cure, it has demonstrated resistance to mogas, (sans alcohol), while others did not. I firmly believe that EZ Poxy, with a POST CURE, will resist mogas with alcohol - even without a surfacing veil.
POST CURE !