|
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
intended for the named addressee only. It contains information that may
be confidential. Unless you are the named addressee or an authorized
designee, you may not copy or use it, or disclose it to anyone else. If
you received it in error please notify us immediately 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.
|