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Scott,
Greg and James are right on. I used to own a business spaying
polyurethane and still have the equipment (except for the spray booth), and
I'm going to take it to a professional shop to do it according to my
specs. Getting it right on the interior is at least as important as the
exterior. You can hose down and wash the exterior; can't do that to the
interior.
Below is a thread from 14 month ago on painting a sub. It's well
worth reading the whole thing.
Have fun,
Jim
From: JimToddPsub@aol.com
Reply-to: personal_submersibles@psubs.org
To:
personal_submersibles@psubs.org
Sent: 3/21/2011 2:55:36 P.M. Central
Daylight Time
Subj: Re: [PSUBS-MAILIST] Paint.....Cheap or
Proper?
Vance and all,
One thing I don't completely understand is the need for
epoxy between the primer and the upper coats of polyurethane instead of just
applying more coats of poly. Is it because you can attain greater
total mil thickness with an epoxy sandwich than you
can with additional coats of poly? Is it because the hard epoxy
underneath improves the impact resistance of the poly topcoats?
I've never sprayed epoxy. When spraying polyurethane,
we were always careful to keep the coats thin enough to avoid skinning over
and trapping solvents within the coat. Trapped solvents will create
pinholes. Generally we were spraying a tack coat and two or three
additional coats.
Jim T.
In a message dated 3/21/2011 2:03:06 P.M. Central Daylight Time,
vbra676539@aol.com writes:
Immersion is a long-term consideration, a category we don't fall into.
UV really isn't a large concern for us in Florida, either, as most of
the subs I know about are stored indoors or at least under cover, and a few
hours exposure doesn't seem to do much harm. That said, any boat owner you
care to check with down here will tell you that epoxy SUCKS as a long term
outer coating. It simply will not put up with years of exposure. That
doesn't make polyurethane easier. In fact, it gets harder, as you have to
abrade the cured epoxy tie-coat to ensure a good mechanical bond
between it and the polyurethane top coat.
Jim, I'm sure your guys know their coatings. However, they are
misinformed as to overall serviceability. If you beat up the epoxy, then you
get zinc exposed at best, and your bare hull at worst. Nine times out of
ten, if you scuff the polyurethane, the epoxy underneath will survive and
protect you until you can get your paint brush out again. Each component
provides additional protection, something to be considered over time.
That said, the new coatings available today are so superior to the old
days that you can use just about anything and, with care, do pretty well. We
spend more time on the trailer than we do in the water, so if you pay
attention, then almost anything you use will provide adequate protection.
Except for Alex, of course. He invented a rust maker. Love to see
that.
Vance
-----Original
Message----- From: kocpnt tds.net <kocpnt@tds.net> To:
personal_submersibles <personal_submersibles@psubs.org> Sent: Mon,
Mar 21, 2011 2:30 pm Subject: Re: [PSUBS-MAILIST] Paint.....Cheap or
Proper?
Hi Jim,
I'm not sure of the correct answer! I know that it's done and do not
know details, however my paint reps were emphatic. I live in Wisconsin and
UV is a much smaller concern than for Vance etc. so I just used the
epoxy.
I would reccomend talking to a knowledgable rep before
purchasing.
Best regards,
Jim K
On Mon, Mar 21, 2011 at 1:13 PM, <jimtoddpsub@aol.com>
wrote:
Jim K,
Thanks much. Regarding polyurethanes, is
there a distinction between a few hours of immersion (2-10) for a small
sub versus much longer in the case of a larger sub, boat bottom, or
underwater structure?
Jim T
Sent on the Sprint® Now Network from my BlackBerry®
Date: Mon, 21 Mar 2011 12:54:03 -0500
Subject: Re: [PSUBS-MAILIST] Paint.....Cheap or Proper?
Hi all,
My two cents!
While there some exceptions, (most notebly moisture cure urethanes)
epoxy is almost always the prefered product for corosion protection
especially in immerssion situations. Corrosion protection is largely a
function of mill thickness and heavy epoxy mastics can be applied at 5 -
10 mils DFT dry film thickness per coat. Most polyurethanes can not be
applied over 5 mils. The rust inhibitive properties are very good with
Sherwin-Williams Macropoxy 646 and two full coats will easily cover the
blast profile of about 4 mils that you will probably end up with. If you
want great shine topcoating with polyurethane is good. I know phil does
this, however my tech reps tell me that polyurethanes do not perform well
in immersion situations.
Best Regards,
Jim K
Kocourek Industrial Painting
On Mon, Mar 21, 2011 at 10:02 AM, Stewart Gardiner
<stew@terminalsolutions.biz>
wrote:
Thanks for clarifying that Jim!
I did mean 2 part polyurethane…. Epoxy being a generic term for anything
using a hardener etc J the particular paint brand ive
used on fibreglass boats before is Norglass or Norcoat..
The
polyurethane primer came out so well I was actually contemplating
leaving it in primer and not worrying about the top coat! J but UV protection might not be
so good with the primer…also its slightly porous…
The
last time I worked extensively with coatings was 1983. We were
using two-part polyurethanes that cost $250 USD per gallon at
that time. Epoxies were considered older technologies that
were becoming obsolete, however I think the term "epoxy" is being used
generically to denote any type of two-part coating (color and catalyst
or hardener).
This is
one of the last places I would try to save money, and I would spend just
as much on interior primers and coatings as exterior for two
reasons:
1. Preventing corrosion is a
lot better than trying to cure it, and having to do that (and redo)
the inside the sub can be a bear.
2. After an operation, I can
wash down the exterior with fresh water and whatever else I chose to
use. That's not an option with the interior.
I've
also wondered about spraying the entire exterior with a wax several
hours prior to a mission but haven't investigated that. Seems
reasonable.
The
first time I sandblasted and painted Snoopy, I put lots of coats
of expensive epoxy on the outside, but had this same exact thought
about the inside. That surely won't get wet, therefore cheap
and ordinary paint should do! Well, when Snoopy was in Florida
the humidity was 100%, the temperature was something ridiculous,
and climbing in and out even splashed a little salt water inside. With
the combination of those three factors, when I was being towed out to
a dive site the inside rusted so fast I could actually see the rust
move. I mean that literally, you could see it popping up from under
the paint, rather like a paper towel that has been laid over a
counter that's sprinkled with water.
I
still don't use as expensive a paint on the inside as the outside, but
one paint I've found is economical yet tough is a two part
epoxy for painting garage floors. It's very thick, giving really
good coverage, and resistant to abrasion. The downside is
there aren't any rust preventers in it because it's intended
for concrete, so you want to spray a base for metals
underneath.
Best,
Alec
The contents of this e-mail are
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and then destroy it.
Im
going to paint the inside of my battery pods today. As
theoretically, the insides should not get wet, i was thinking of using
just a normal metal paint like Hammerite or something. A
straight forward paint that you would use to paint outdoor railings
and things with. Do you think this will be ok or should i go for
the "proper" 2 part epoxy marine primer? Its just really
expensive.
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