RE: [PSUBS-MAILIST] goop and sealers

Jim makes some good points which I support. We use an aliphylactic (SP?) two-part polyurethane epoxy on and in our tanks that hold brine water that is used in our RO production of potable water. This is several thin coats sprayed over a zinc-rich primer on the outside (a plain primer compatible with the epoxy is used on the inside that is suitable for drinking water systems). The thin coats allow proper curing and venting of VOCs. As Jim noted, there is some minor chalking after 10+ years exposure daily to the bright sunlight of the tropics on our white paint (much heavier chalking and fading on the contrasting orange but this may be due to improper application). These were applied by specialists in the field and the more recent touch up, I observed that temperature and humidity was noted in the preparation of the proper mix of the epoxy and thinner. Adhesion has been excellent in the brine tank, especially at the air/water interface where the most corrosion is expected to occur in the 100% humidity of the interior. These paints are pricey but more than pay off in their longevity. They would not be suitable for the thick protective coating for wiring penetrations that Frank speaks of. If the exterior of the sub painted with one of these epoxies was waxed every once in a great while, chalking would not be an issue.

R/Jay

Respectfully,

Jay K. Jeffries

Andros Is., Bahamas

Vive vt vivas
— Live that you may live

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jim Kocourek
Sent: Saturday, May 10, 2008 09:57
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] goop and sealers

Hi Hugh,

In the US the paint that you are refering to is called Direct - to - Rust or Epoxy Mastic. It is a very heavy bodied paint and works well. Of coarse, it is still not nearly as good from a longevity standpoint as sandblasted profile coated prior to flash rusting. While I'm not sure what you are painting, the best system for our uses is Sandblasted profile coated with zinc-rich primer first. The zinc rich primer is a sacrificial primer which primer gives itself up in stead of rusting when conditions are suitable for rusting, such as high humidity, alkalinity etc.and acts as an anode. This first coat should be coated with a second intermediate coat of high solids epoxy similar to the Epoxy Mastic described earlier. After adequate cure this shoud be topcoated with the approprate topcoat. The topcoat that will perform well is a good quality epoxy also, however they tend to chalk and fade quickly. Polyurethanes are much better at retaining gloss and chalking resistance, but do not perform as well in immersion envionments I am told. I am still not sure what I will use as a final coat. Possibly a moisture cure polyurethane.

Best Regards,

Jim K