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Hi Stew,
True epoxies tend to be brittle and have poor UV resistance. But
remember my experience ceased about 28 years ago. The deterioration or
defects in coatings start out as being microscopic. The damage is
happening before you can see it.
Primer only looks inward and is designed to adhere to, seal, and protect
the metal or other surface and provide adhesion for the next layer of
coating. It's generally lacking in components to protect it from the
outside world, although there are some that claim to combine primer and
topcoat. That claim would have to be proven to me especially in such a
hostile environment as sea water or even fresh water for that matter.
Bonding between materials and coatings can be either chemical bonding or
mechanical bonding or a combination of both. One of the considerations
that affects that is time between the different types of coatings (primer,
secondary coating, and any subsequent coatings. By coatings I mean
different materials as well as multiple layers of the same material.
Either too little or too much elapsed time between coats can adversely affect
bonding. Temperature, humidity, and ventilation can affect that
time.
I will likely contract much of my coating work to someone with the
equipment, facilities, and commitment to do high quality work. Most
businesses want to minimize the time their spray booth is tied up on one job, so
they recoat as soon as possible.
One hint I would offer whether you're doing the work yourself or
contracting it this: Alternate the color of your coatings between
layers. This makes it much easier to ascertain that you have even,
complete coats. It also makes any subsequent scratches show up more
easily. That's might be bad for cosmetic appearance, but it's good for
finding and correcting breaches in you coatings.
As Vance mentioned, there have been some real developments in the
engineering of marine coatings in the past few years. About a year ago I
was reading of a bottom paint that has extreme resistance to barnacle adhesion
and other nasties of sitting in water. It was not yet released to the
market at that time. Sorry I don't have any more information on it.
Cheers,
Jim
In a message dated 3/21/2011 10:11:01 A.M. Central Daylight Time,
stew@terminalsolutions.biz writes:
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…
From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
JimToddPsub@aol.com
Sent: Tuesday, 22 March 2011 1:27
AM
To: personal_submersibles@psubs.org
Subject: Re:
[PSUBS-MAILIST] Paint.....Cheap or Proper?
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
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From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of James
Frankland
Sent: Monday, March 21, 2011 6:06 AM
To:
personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST]
Paint.....Cheap or Proper?
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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