Epoxy for composite tank

[buzznichols]

Sooo...

I'm gearing up to tackle a composite (fiberglass and kevlar) tank build. I've been researching epoxies, and everybody seems to agree West System is the bee's knees. However, that stuff is damn spendy and I'm on a shoestring budget. Marpro makes an epoxy that says "compare to West Systems" and it's a heck of a lot cheaper. However, I don't really know what it is I should be comparing chemically. I'll be laying it up on an EPS foam plug, so vinylester is out of the question.

1st: does anybody know anything about Marpro epoxy, or what chemical properties I should be looking for in an epoxy for a composite tank?

2nd: If I lay up the first couple layers with epoxy (West System or whatever), can I then switch over to polyester/vinylester/whatever without the resins seperating or otherwise disagreeing?

 

[J-Rod10]

Poly and epoxy don't always play nice together.

If you are building a tank, spend the money on the material, your life may depend on it.

 

[cxman]

most builders and fabricators of fiber plastic and marine fuel tanks use caswells

due to its reliability and resistance to ethanol and other stuff

i think its this stuff but i dont know shit so call them they will tell you what to use and how to do it \

http://www.caswellplating.com/restoration-aids/epoxy-gas-tank-sealer.html

 

[buzznichols]

I'm definitely planning to coat the interior with Caswell's when all is said and done...I would imagine, given that, that I could get away with nearly any epoxy for the actual composite wetting out/buildup. It's just, as J-Rod points out, the stakes get pretty high when you're dealing with a gas tank.

 

[jpmobius]

I have bought from this guy exclusively for many years. Highly recommend you do the same. I do not believe you can acquire higher quality material regardless of cost. I use epoxies exclusively for bikes as the small scale makes the relatively high cost tolerable. For most of my own work, the fabrics are far less important, so I usually buy local, and generally don't waste money on carbon-graphite-etc (very cool, but not worth the trouble and expense for negligible functional benefits for most of my work) but ALL my epoxy comes from here:

http://www.epoxyproducts.com/

look in the marine section, the site is sort of expansive, but a lot of good info if you wander around.
I buy this: http://www.epoxyusa.com/Premium_No_Blush_marine_epoxy_p/me15.htm
and this: http://www.epoxyusa.com/Wet_Dry_700_epoxy_putty_p/te05.htm

I think he has smaller quantities, but remember, building a tank is a crazy amount of work, and the cost of materials will at the end be irrelevant. Also, these are high caliber chemicals and have for practical purposes an infinite shelf life, so they will still be good years down the road for future work.

I would respectfully add, that if you are not accustomed to engineering/fabricating with "exotic" fabrics (kevlar, carbon, etc), you may find life simpler and happier with fiberglass. The exotics are not significantly lighter (or stronger) without the engineering and fabrication techniques to go with them. Just way more expensive and harder to work with.

Also, use rigid urethane foam for your modeling, not EPS. You can use green florists foam, the last I used was impervious to epoxy. That stuff is rigid urethane, but hard to find big enough pieces to avoid a lot of joints, but you can glue blocks together with solvent based contact cement (not water base). The best economical foam is industrial urethane insulation foam which is gold (actually naturally tan) colored and comes in big (3' x 6'?) sheets. Much better for a tank and very cheap. It is low density 2Lb/CuFt or less but getting hard to find. Modeling foam is exactly the same material, and the absolute cat's meow at 4-6 Lb/CuFt, but it is very pricey.

 

[J-Rod10]

Yeah, Kevlar/carbon are a bitch to work with in a hand lay-up application.

 

[buzznichols]

Wow. That link really leads to a ton of information - it's like drinking from a firehose. Thanks a bunch!

So, the responses have led to a third question: does adding a couple layers of kevlar add any desirable properties to a 'glass tank, or should I just go straight fg/epoxy?

 

[jpmobius]

Well, it will be significantly harder to file all the way through when sliding down the pavement, but psychological peace of mind is likely the only true benefit. It's sort of like designing a crash helmet: Do you design for high impact at the great expense of everything else (super unlikely) or smaller impact (super likely) but give up the high impact protection? Very very hard to do both, so choose your odds. Bad if you bet wrong. For me, I'm thinking my tank will probably not get speared by something and punctured, nor will it get a hole filed in it. Probably it will get a heavy blow that will cause a seam to split or simply bash a crack in it, so I would design around the most likely scenario.

 

[J-Rod10]

Can you better lay out your process? And why vinyl ester is out? Vinyl is pretty much designed for petrol applications.

 

[buzznichols]

I'm going to lay it out over an EPS foam plug, and according to my research (such as it is), vinyl ester will melt polystyrene. I'm planning to build it in one piece, then dissolve the foam plug with xylene. Once the interior is cleaned out, I'll coat it with Caswell. My inspirations for the process were the hack-a-week VF750 Sabre build and (of course) Ringo's CB 550.

 

[jpmobius]

Maybe you will not have fun dissolving the plug. I did this ONCE, and it will not be attempted again. There are other reasons for an alternative method. Building in two pieces gives inside access to the filler neck/cap and outlet fixtures. However you have seams to join. Both schemes have merits and drawbacks.

 

[buzznichols]

That's what I'm finding.

I opted for the plug dissolve method because my bike has 2 frame rails, so it's relatively easy to create a jig to replicate the bottom of the tank. The 2 frame rails is, of course, also the reason I can't just snap up a tank I like and deal with fitment. Most of the really cool tanks out there (and, as nearly as I can tell, all of the off-the-shelf cafe tanks) fit a single frame rail.

I'm really curious what issues you (or anybody else) ran into with dissolving.

Thanks,

Buzz

 

[jpmobius]

Well it was a loooong while back, but I recall 3 things. It was crazy hard compared to what I expected (a Styrofoam cup may seem like it dissolves like a sugar cube in hot water, but my core did NOT). It was messy beyond description, and wasted a zillion dollars worth of solvent (think I used acetone - then gasoline maybe). But the worst thing was that I never felt like I got the inside really clean. Couldn't get that last surface clean down to the glass. I did get it done though, but think I abandoned the tank to go to something else not long after I made it. Damned if I can remember what ever happened to it. I'm sure I did not use epoxy back then too, which may have been a factor. I use urethane foam for everything now and either scrape it out, which is really easy, or cover it like a mold if big enough to be practical. Sometimes it just gets left inside like in a small seat hump - weighs next to nothing.

 

[buzznichols]

Interesting...

The hack-a-week guy (Dino something - neat guy, interesting build, very addictive YouTube show) settled on Xylene over acetone...he said it "worked better" but was not more specific than that. He used a single gallon, along with some bolts, to clean out a 4+ gallon tank, and it appeared pretty straight forward. of course, the magic of television...

Anybody else got insights on this subject?

 

[J-Rod10]

One, and the main, downside to it, is you will not have a gelcoat top coat. Gelcoat is hard, it keeps the glass in its place.

 

[J-Rod10]

Not to mention gelcoat keeps the glass fibre from poking out randomly and fucking up your paint.

With a $15-$20 quart of gelcoat from US Composites, you would have more than enough gel to make a proper mold, and then a tank.

 

[jpmobius]

Not really seeing any value to adding gelcoat to a mold-less composite fabrication, unless for some reason you want gelcoat as the final finish. If you are making a mold, or of course a part from a mold, gelcoat is practically a requirement if using conventional methods.

If you do decide you want gelcoat, make sure you know the difference between laminating and finish gelcoat.
Laminating gelcoat will not develop a hard surface if exposed to air.

Gelcoat IS really thick and would cover a lot of sins in the fabrication, but a little care eliminates this necessity. I use an epoxy automotive primer as a first coat directly on my fiberglass and epoxy fabrications, and proceed with normal finishing techniques. Never had any sort of issue. This seat cowl was made pretty much exactly as your man hack-a-week's tank (except w/urethane foam), and it couldn't have been easier to paint.