Date: Sat, 4 Jan 2003 15:13:17 -0500
Reply-To: Jonathan Farrugia <jfarrugi@UMICH.EDU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jonathan Farrugia <jfarrugi@UMICH.EDU>
Subject: Re: LP tank--Epoxy paint V.S Urethane paint
In-Reply-To: <e6.33ecd553.2b4830b3@aol.com>
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the rust moving under the paint while the paint is still intact is
referred to as creep. creep is very common in most powder coat
applications, that is why i would suggest against powder coating the tank.
powder coat looks real pretty and has a hard surface but has poor creep
resistance characteristics. i did some reading about powder coating in a
paint research journal (i don't recall the name) and there are some powder
coatings designed to resist creep. i think that you would have to buy in
larger quantities to obtain them.
the red "lead" primer is still available from sherwin williams or a least
it was about a year and a half ago. i personally use acid etching primer,
but you should be careful when using it because it only has a short pot
life. it will spray and look okay after its pot life is over, but the
acid will no longer be doing its job. the primer is a two part basically
an acid and a vinyl. the vinyl encapsulates the acid so that you can top
coat it with out having adverse reactions. the acid primer should be top
coated 8 to 12 hours after final primer application.
i use the acid primer because of it superior creep resistance. there are
better primers if you want better protection from creep. the best in my
opinion is zinc primer. this stuff is basically galvanization in a can.
the problem with using this stuff is that it is a suspension of zinc
flakes in a solution. in order to keep it in solution it has to be
constantly stirred, so you need a spray gun with a stirrer. if you were
really cheap you could probably get by with constantly swirling the gun
around to keep the flakes in solution.
one final note when selecting coatings to resist rust. you want to get
the manufacturers data sheet and look at their salt spray testing numbers.
the salt spray test is commonly conducted by most coatings manufacturers.
they stick some coated piece of metal in a plastic chamber filled with a
calibrated salt solution and spray salt water on it until it starts to
rust. they then record how many hours of spraying it took to rust. this
is certainly a simplification of the process but it should suffice to get
the point across.
finally no good coating will work unless the surface is properly prepared.
i would suggest that you have your tank bead blasted with some where
around a number 10 glass bead. if you use a coarser bead make sure that
you can spray your coating over it, check the manufacturer spec. the acid
primer isn't supposed to be sprayed over a blasted surface. the blast
profile is to jagged for the vinyl to reliably cover. i have used the
number 10 bead with fairly good results, because its blast profile is
fairly small. the other option is to use coarser media and hand sand it
after blasting, which i find to be a bit annoying.
jonathan
> Phil, my man, epoxy paint is certainly tough as nails and it will stick to
> nearly anything, still, it is not infallible. Years ago in the Salt Belt,
> when epoxy paint was the latest and the greatest the guys who used it on
> their cars found that it posed one major drawback. If it gets chipped, a
> rust center can start and under that tough protective coating the conditions
> are just right for the rust to spread. I've even seen rusted through panels
> with the epoxy paint still intact. Also, it is a major bitch at refinish
> time.
>
> >From my own experience, there is nothing better for rust prevention than red
> lead primer, but if you do not have any already it may be impossible to find.
> If you talk to an industrial coatings guy he will surely be able to
> recommend some less illicit alternatives.
>
> George
