I guess we are going down this rat hole...
First off, let's try to keep things factual - you mention quite a few things that have some technical basis but statements like "There is just no competition.." are your opinion, and I definitely disagree with you. There certainly is competition between the two materials; and as I've said before, I have no problem with epoxy, but let's stop saying polyester is "unsafe" or that it doesn't stack up.
mmm... Where did you get that I said it was unsafe? You seem to be putting words in my mouth there? I'll stand by Epoxy being a superior product over Polyester all day long though. In truth, Polyester is the lowest grade of all resins. That is not opinion but just simple fact. There's a reason Epoxy cost more.
1) most of your pro/con arguments have to do with mechanical properties that don't really matter much in these applications. (Abrasion resistance, really?) The tensile strength, fatigue resistance (again, really?) and so on of both materials are more than adequate for the job, provided a half decent plywood base structure is in place. Kevlar cloth has better mechanical properties than glass cloth too, are we going to start lining tanks with that? No.
How does abrasion and tensile resistance not matter in an aquarium. Better abrasion resistance will give the tank better wear over the years. Better tensile strength means the tank will be less prone to damage from dropped rocks, ornaments or objects that could cause damage with in the aquarium.
2) Several other of your pro/con arguments (Pot life, ambient temperature, mix ratio) have a lot to do with application technique and personal preference, so are hard to consider an advantage either way. I personally find Polyester easier to mix than Epoxy as you have to screw up the ratio pretty badly for it not to cure at all, much less thorough mixing is required as well. Also, ambient temperature affects ALL thermoset plastics, including epoxy. If it's curing too slowly for your taste, add a space heater.
Yes, you are correct. Ambient temps affect all resins but Polyester more so than Epoxy. Hence why the use of a light-box to pre-warm Epoxy before use is a common practice. No one in their right mind would apply this practise too Polyester. I'll give you personal preference on mix ratio.
3) In my neck of the woods epoxy tends to be more like 3 to 4 times the cost of polyester, if it's available at all from local vendors, and no, you don't need to use more polyester unless you're making the whole tank structure out of FRP. The point is to create a barrier, not a structure.
At 4x the cost I can understand why one would choose polyester. If this were true, I would probably be shopping elsewhere or maybe online. As for not needing more Polyester unless structural. That's just wrong. You don't line the inside of your tank with fiberglass for structural reasons but you do want to know that that impermeable barrier will still stand up to damage from fish, rocks, substrate or anything else that can cause damage in the tank over time. As stated, the same strength barrier can be achieved with a thinner laminate when using Epoxy. This point is very relevant, especially when one wants to compare prices.
4) You mention styrene - and that is a consideration for people who have to work indoors. You left out however that many people have (or can develop) skin and lung sensitivities to uncured epoxy, which is why most manufacturers recommend against spraying their products (A significant disadvantage IMO, as there's no better way to get a nice even coating). I for one can say I was covered in unpleasant hives by the time my first epoxy tank was complete, but I was dumb enough to get it all over myself, so... anyway, moving on.
Correct. I did leave that out as it is not a common thing. Especially as it also really applies to more of the earlier Epoxies that use a high ratio mix. Use a low ratio mix Epoxy and this will pretty much be a non issue nowadays. As for getting it all over yourself...I think you could guess what I'm thinking.
5) Polyester Gelcoat IS polyester. It is not required for water barrier, it is added for color and UV protection. I also fail to see this as a disadvantage - Gel coat is cheap and looks good once applied; in my polyester build I applied gelcoat directly to lumber in quite a few places where I didn't add fiber reinforcement. You will note that most epoxy construction boats use epoxy gelcoat to finish as well for similar reasons.
Polyester Gel Coat is not the same as Polyester resin. It has the introduction of other pigments, modifiers and other components to make it a better water barrier. Polyester resin is not waterproof at all. Epoxy resin is completely water proof on its own.
6) The final layer of polyester does NOT require wax. In my build I used a product called PVA that is dirt cheap - you spray on, let sit, wash off, done. If you do take the easy route and use waxed resin, it's no more expensive and does the job in one step. I fail to see how this is a noteworthy disadvantage.
Not trying to be rude but I remember someone getting water marks, blemishing in the surface of their last layer because of not having the correct addition of 'wax in Styrene' and then covering it with PVA to try and get the last coat to cure correctly. The end solution was to paint over it with Krylon Fusion paint. Sound familiar? If that does not give an example of why my statement is relevant, I don't know what is.
7) Epoxy products cannot be used with a chopper gun. This is not really of concern for most of us, but for larger scale projects like Pete's here it becomes a consideration.
A true statement for the most part.. Personally, I would hand lay a build like Pete's as chopper guns tend to use a higher resin to reinforcement(Chopped Strands) ratio. A hand layed lamminate is also stronger.
8) Epoxy products are not compatible with chopped strand mat; they require a special stitched or woven fabric, which lacks some of the workability advantages that regular chopmat has.
Totally correct.Woven mats are harder to manipulate but are much stronger
9) Where did you find your 7-9% number for shrinkage? That is a totally ridiculous overstatement of reality. It does shrink a bit as it cures, particularly if you mix it hot, but nowhere near that much. If that was the case the entire lining in my 600 would have pulled away from the walls by 6" or more.
It's common knowledge how bad the shrinkage rate is with Polyester. It's one of the reasons more have switched to Vinylester over the years. In saying that, I think you may be taking that as shrinkage from end to end. It's more so shrinkage from front to back. It's why you end up seeing the reinforcement imprints etc photographing through to the outside. Even through Gel Coats over time.It is also one of the reasons for micro cracking.
Anyway - this is all good information to consider, and once again I'm not trying to dump all over epoxy - it IS a superior finished material, but the real world tradeoffs are cost and difficulty of use (IMO). It's a totally legitimate choice for a tank lining, but it doesn't blow polyester out of the water, it's not "No competition", and polyester is definitely as fish safe as any of the other products the MFK userbase has generally accepted.
