How to protect aluminum scupper from corrosion when aluminum is in touch with concrete or concrete block?
Bituminous coating on the backside?
I always recommend against using aluminum in contact w/ concrete or msry, since it’s difficult to ensure that it will be properly isolated. In addition, joints in aluminum scuppers are usually sealed, making them prone to failure. Stainless-steel or another weldable metal solves both shortcomings, so that’s what I always suggest to my clients.
Bituminous Coating has certainly been the “industry standard”, but its messy to use, Contractors hate using it so sometimes they use nothing.
Stainless steel is expensive, I spec stainless on the high end, luxury projects.
Galvanized metal does not last long in South Florida, with all the salt in the air.
Therefore I am looking for a coating that is relatively easy to apply, and “inexpensive”.
For a while I was specifying SW Loxon, but SW won’t warranty the use.
Latest possibility is a Fast Cure Epoxy like SW Macropoxy.
Automotive paint?
Lynn, I am not a car geek, care to be more specific?
Seriously, paint used on the exterior of a car, a lot of which is aluminum, and withstands pretty much anything that can be thrown at a car. Except maybe another car. You can get touch-up paint in spray cans. Candy-apple red, anyone?
Water based acrylic polyurethane paint is the most popular automotive paint, my SW Rep is looking into a spec.
Lynn,
My favorite color.
My 2016 H-D road king is candy-apple red.
I’ve had polyamide epoxy coatings recommended instead of bituminous coatings. They are two-part like many epoxies but are easier to work with than bituminous coatings and probably more environmentally friendly. I’ve been specifying polyamide epoxy for aluminum in contact with cementitious materials for a few years now and have had no push back from contractors. That doesn’t necessarily mean they are following the specification. 
One example of the product is Sherwin-Williams ArmorSeal 1000HS.
How about strips of self-adhered asphalt (or butyl) based membrane (Henry Blueskin, Grace Vycor, et.)? It is easy to apply (no waiting for coatings to dry) and the installer probably already has it in their truck.
I like David’s idea.
Self-adhered asphaltic membranes sound OK, clean solution, as long as they are on fully-concealed surfaces of the scupper; the membrane will degrade on prolonged exposure to UV. Also, it will act as a bond-breaker with concrete, so need to detail accordingly
I know we are refering to aluminum, the American Galvanizers Association states:
“Paint is not a reliable method of deterring the return current path of the galvanic cell; rubber or some other insulating material would be best for that.”
As David wrote, a rubberized self-adhered membrane.
Wayne
Aluminum is reactive in the presence of “fresh” concrete or mortar. I am not sure how reactive it is when the concrete or mortar has cured. I believe it is the free alkakis that could create a problem, but once the concrete or mortar has cured I don’t think it would be as much of a problem. Putting any kind of coating may be enough.
I always spec’d what David suggested - peel and stick sheets. It’s easy to get, easy to do, and reliable.
Thanks for all the input, I am going to provide 4 possible solutions:
Bituminous Paint
Epoxy Paint
Water-white methacrylate lacquer (called out in the Building Code
or Self Adhered WP Membrane
let the GC select the product.