As the title says. I'm looking for the least toxic paint to go on a galvanized corrugated metal roof I installed some time ago.
It's starting to rust and I really need to paint it.
When I find a paint I'm willing to try, I plan on painting one side of the roof(two sided roof structure), letting the paint cure for weeks, then collect a sample and get it tested. All this while using the water of the other unpainted side. If test results are fine, I'll paint the other side and collect from the previously painted side.
I use this water for bathing(4 drops of bleach per gallon), cooking, and drinking(boil and filter throughly).
Am I being too paranoid about this? Are most roofing paints safe?
This might be a stretch, but if your roof is getting rusty, painting it will not stop the rust, but only slow it down.
One option would be to get up with an angle grinder or wire brush and physically remove the rust. Unfortunately this will also remove adjacent galvanized coating and make the underlying metal even more prone to rust.
Option two might be to chemically treat the rust spots with a rust converter. I have done this on some metal odds and ends and the rust chemically turns to a hard black coating that positively resists further rusting and acts like a primer surface for painting.
The easiest to use source I have found is Gemplers rust converter (from Gemplers.com).
I realize this is not the paint you were looking for, but painting rust is just about guaranteed to create little rust bubbles over time.
Off hand, I would think that a polyurethane pant possibly is the best option as it tends to form a very hard, stable coating. I honestly can’t say if this falls under the “organic or better policy” but as we are talking about paint, I don’t really know what is acceptable and what isn’t.
Fair point Eric, but when I hear people speak of painting rusty metal, I assume they will do it according to instruction, which will include,
removal of loose rust, use of converter and application of coats of paint as per the instructions.
The result will be a good quality repair.
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan
Actually I agree with you. The best way to use the rust converter is to first reduce to a minimum the amount of rust to convert. And yes, this usually involves physically abraiding the surface rust and removing the debris.
What I wanted to contrast was the practice of removing EVERY last trace of rust. Doing so inevitably removes excess galvanized coating and leaves the metal even more prone to rusting later.
If one can remove just the outer, flaky, easy to remove rust and convert the rest. One stands a good chance of halting the rust altogether. Naturally this also involves getting something on top of the galvanized surface to really shed/resident further water attacks. I would be tempted to use a good polyurethane paint/coating, but I just don’t know how/where this fits into organic or better.
John, thanks for pointing out my somewhat generalized description of how rust converter works and how to better use the product.
Permaculture. It’s a journey, not an event.
Location: Puerto Rico
posted 1 week ago
John C Daley wrote:Make sure you buy a roof paint that specifically says its safe for potable water - Dulux, Wattyl etc do make them
All the paints I found, even articles talking about safe paints for roofs, come from that area, AU and NZ(I think I saw one from the UK). Apparently, collecting rainwater is big over there.
In the US, and on this island, people depend on their tap water, heavily. The only articles I found speaking of rain harvesting and health are about studies on roof materials, things that come already treated, meaning if you want to collect good water, you might need to strip the old roof off, send to a landfill, and buy new roofing material. I'm not doing that, even if it was within my budget.
Doesn't look like they make a paint for old galvanized corrugated roofing material.
By the look of the site, their projects, and their products, it doesn't look like I could pay for anything they offer. Some high-end stuff.
I'm just trying to prevent leaks while being able to use the water for hygiene and drinking. The closest municipal water connection is like 800 ft away, and I really don't want to depend on those dumbasses.
The finish doesn't have to be nice, and I'm thinking of replacing the roof between 6 to 8 years from now. This roof was an emergency installation. The house had its old roof blown by Maria and I had a heavy duty tarp for about a year. Now we're here full-time and although no leaks are present, with this weather of intense sun(good for the PV panels hehe) and +120" yearly rainfall, I'm estimating leaks in 1 to 2 years. The galvanized coating is microscopically thin.
Location: Puerto Rico
posted 1 week ago
I'll keep looking and if I do end up painting it with some Home Depot rust inhibitor paint/primer, I'll test it and you'll know about it.
I can harvest enough water with one side of the roof, so I can afford to lose one side to a toxic coat.
I don't want to have to get Galvalume for the collecting side... But we'll see.
All further suggestions are much appreciated. Thanks, everyone.
Hey, sticks and stones baby. And maybe a wee mention of my stuff:
2020 Permaculture Design Course for Scientists and Engineers, June 14-27