Metal Roof Coatings

[1voyager1]

Our roof is about 10 years old now.
It is beginning to form large black areas that appear to be something similar to the steel corroding under reducing conditions, or a residual from the original finish degrading.
I'm certain that it is not mold, mildew or other similar type growths.
It is also forming minor rust areas along the lower edges.

We are looking into refinishing the roof's surface.
The problem I'm running into is finding a coating for the metal roof that is suitable for a potable water catchment system.
Nothing that HD or Lowes carries is obviously suitable, or is obviously unsuitable.

In looking around, I am drawn to GAF's TOPCOAT Membrane WOB, but cannot find a source for it in Hawai'i.

Anyone know of a local source for this product or others suitable for this use?

[Tink]

Check the areas that are black for blistering, if so, panel is shot, as corrosion is too deep.
As far as painting, I would investigate an acrylic enamel, or enamel base paint, both used in automotive and roofing panels that are not anodized or powder coated, as adhesion and wear are excellent. Residuals are I believe, a minimum. Check the Material Safety Data Sheet (MSDS) when you find the product you are interested in. These paints use a reducer/hardener to make that impermeable surface like an epoxy paint.
Don't know if HPM sells it under their Sikkens paint line, but you could also check the Auto Supply Center in Hilo, or maybe Napa in town.
These are all spray based paints unfortunately, when you use the hardener, although you may find brushable or roller applied enamels there as well.
Best of luck!

Community begins with Aloha

[Bullwinkle]

EDPM rubber based sealants may be a good solution ...I have been researching the same issues - https://secure.websolhost.net/@epdmcoatings/order-v2/

[EightFingers]

I'm amazed a ten year old roof is having the problems you describe. Ours is also ten years old and we don't have any of those problems. Maybe the contractor installed some used panels. Metal roof should last at least 30 years.

[1voyager1]

I've been a bit busy and have just come back to see what replies I've gotten.
I wanted to get some down spout screens installed and my catchment tank vacuumed before Hilda comes to visit.
By everything right and proper, we should have no more leaves and other odds and ends going into our tank.

@ Tink
The black areas do not seem to be actual corrosion.
The surface is smooth, hard and covered by a very thin layer of a dusty type substance.
I think it is likely to be the primer coating under the original paint of the panels.
The only actual corrosion seems to be the lightly rusted areas along the bottom edges of the panels where they were cut to fit.
The raw edges were undoubtedly not sealed from the weather.

I do not trust automotive finishes to do a proper job for a potable water collection surface.
Nor do I trust the MSDS's to give the proper information needed to identify it as suitable for that use.

@ Bullwinkle
Yep I agree, an elastomeric type coating is the way to go if it has certifications for catchment system use.
I'm still partial to GAF's TOPCOAT Membrane WOB.
There are certified installers for it in Honolulu, but no where else that I can find in Hawaii.
I wonder if they might be a source to obtain the coating.
If not, there is probably a source in California convenient to Matson's facilities that could ship it here.
A quick and dirty calculation that may have errors gives me 2500sqft roof, not considering slope.
With 1 to 1.75 gal / 100sqft at 12.5#/gal gives 5 to 10 65# 5 gal buckets making a 350 to 650# shipment.
I think it is doable.
I still haven't checked on the cost of the coating and comparing it to the cost of a new roof.
Nor have I looked at alternative coatings yet.
We're a long way from making a decision on this.

@ EightFingers
This is the original roof from when the previous owner had the house built.
The panels are probably the cheapest the contractor could get from HD with no concern for longevity.
I'm convinced the finish is degrading, and want to get it refinished before extensive corrosion sets in.

I might add that I walked the roof with the home inspector about a year and a half ago.
He said that the roof's condition was not out of line for its age, but the rusty edges would need attention before the rust got too bad.

[Malapuaao]

>>Metal roof should last at least 30 years.


Drive up by Volcano Village sometime, you'll see either brand new roofs or else totally degraded roofs only 5-10 years old.

aloha

[Tink]

Check out the MSDS on the GAF topcoat. Interesting. I would check thoroughly whatever product you choose by reading the Safety Data Sheet first, and use it as a guide for your coating choice. Also consider "breakdown" particulate of whatever you use from VOG, UV, etc.. Original panels were probably powder coated with an epoxy base application, thickness of powder coat determines "life" under testing of normal UV and climates, but not VOG.

Community begins with Aloha

[1voyager1]

@ Tink

MSDS's are very useful and have good information for using what ever it is describing. But, unless it is for a material specifically designed for potable water systems I think you're giving too much credence to the info contained in them.
You will not get the applicable information you need to make that decision.

From GAF's website:

"TOPCOAT® Membrane WOB White is included on the list of approved potable water catchment coatings by the Bermuda Department of Health. TOPCOAT®Membrane WOB White has been tested and certified by the NSF International as an approved potable water catchment coating that complies with requirements of “NSF Protocol for Health Effects of Rainwater Catchment System Components dates August 1, 1995.” The ingredients of TOPCOAT® Membrane WOB White are listed by the U.S. Food and Drug Administration."

Before actually committing I would verify these claims.
For now, I accept them in deciding which ones to consider.

Plus, I had forgotten to mention that the white non pigmented coating is rated at 85% reflective for cutting heat transference through the roof.

[Jay Bondesen]

I'm not sure how much luck you will have finding many choices that can be field applied and also labeled suitable for potable water. Or how long that rating will stand after exposure to weather. The coating would likely need to be re-applied regularly. I didn't check but I don't think new roof panels from HPM carry that 'suitable' label. I guess the problem is that most coatings degrade over time and leach out components that individually are considered hazardous. The GAF product has either a 5 or 10 warranty based on how thick you apply it. Meaning it gets thinner over time and some of it blows or washes away. They did leave out a couple of heavy metals that most exterior paints have in them to reduce mold growth.
The most weather resistant coating material I have experience with is silicone. On the other hand there are filters that remove most or maybe all contaminants. So there is roof integrity and drinking water. Maybe they are separate issues.


Jay

[1voyager1]

@ Jay Bondesen

The warranties are only available if applied by a certified applicator.
If I apply it myself without having become certified by GAF, I will be providing my own warranty.
I screw it up.
I fix it.
If properly applied as GAF would train an applicator to do, a ten year life would be the minimum I would expect from it.
That looks to be better than what I'm getting from the present roof panels.

I can read specifications.
I am capable of making the application as GAF requires it to be done.
The only question is:
Do I want to?

In my searching around I only found, I'm guessing right now, maybe about 3 or 4 products suitable for this application.
The only one I've begun to run down info on is the "TOPCOAT Membrane WOB" product.
My first impression was that it is likely the best product choice for the job.

Note that WOB stands for Without Biocides [no mold, fungi or other vermin inhibitors]