Painting inside of galvanized stock tanks (underwater use)
Use as swimming pool?

A. Hi folks. Galvanizing can be very difficult to paint for several reasons, but one of the problems is that zinc (galvanizing) plus alkyd (oil paint) "saponifies" (turns into soap). Obviously this soapy layer at the interface of the galvanizing and the paint makes for an impossible situation, and you may have seen paint slide right off of galvanizing because of it. You must use a latex self-etching primer after scrubbing the surface down and rinsing it, but preferably after letting the galvanizing age for a year.

This is still not an absolute guarantee of success (in industry, zinc which is going to be painted is first zinc phosphatized), but at least you'll have fair odds with the latex self-etching primer :-)

Regards,

A. Hi Cynthia. I am not familiar with that, so I can't call your hardware man wrong. But the American Galvanizers Association has a nice webpage explaining the situation and the suggested approaches ==>

Luck & Regards,

A. Hi Brooke. Zinc boils at 1665 °F and is emitted as clouds of vapor in the air at higher temperatures than that.
Zinc is not a poison or a toxin; rather it's an important micronutrient. Cold-easing tablets for example are zinc and are deliberately ingested. But if your husband were to weld zinc-coated things with poor ventilation or an improper welding hood he could inhale those clouds of zinc vapor and get sick due to the huge overdose. The hottest of hot summer days can't get the tank to anything remotely approaching that temperature; your house and yard would burst into flames long before you were halfway there :-)

Luck & Regards,

A. Hi Lonnie.

When it is known that a galvanized surface will be painted, it is always zinc phosphatized or annealed in a factory ... and that is the "correct" approach to the problem, as universally practiced on automobiles and other mass produced items.

Paint, even specialty primers, sometimes sticks poorly to galvanized surfaces -- which can have varying degrees of weathering, variable degrees of chromate quenching, and a tendency to saponify (turn to soap if exposed to alkali), etc. All you can do is your best and keep your fingers crossed; often it works fine.

I think a scrub brush [on eBay or Amazon] and powdered pumice [on eBay or Amazon] for cleaning, followed by a 1:1 vinegar/water neutralizing/etch, followed by rinsing, followed by a latex primer designed for painting on galvanizing are your best bet; I am not personally familiar with any specialty primers designed for under-water use on non-phosphatized galvanizing, so priming as described followed by your epoxy paint may be best for indoor use. But epoxy has no UV-resistance, so if this is for use outside you may want to put a top coat over the epoxy or go with a polyester or type of paint instead.

Luck & Regards,

A. Hi Franny. Millions upon millions of infants, and older people as well, bathed in galvanized washtubs. Further, if this tank was intended for feeding or watering livestock, it's reasonably safe to assume that it won't leach substantial amounts of toxic materials. And as Paracelsus told us 500 years ago, the dose makes the poison.

Still, as an engineer, I must repeat the mantra that the designer intended this tank to be used for a different purpose and when we repurpose something we do not know for sure that the choices he or she made are compatible with the new application. Livestock feed tanks are probably sufficiently resistant to low concentrations of chlorine, bromine, and other water treatment chemicals used in hot tubs to not pose any danger beyond the Paracelsus point, but the designer did not have those chemicals in mind.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey