MITRA Forum Question Details

The main concern with painting on ACM panels is always adhesion. You want to ensure the surface is prepped in such a way that you do not encounter scaling, flaking, delamination, etc. down the road. In the meantime we have sent your query out to some who are more knowledgable in this area who may be able to weigh in with their expertise.

So anodized aluminum surfaces can really range in the sense of composition (e.g. is the aluminum sheet itself an alloy as opposed to pure aluminum? You might want to avoid any zinc-containg alloys for example), pore size, and the method used to seal the pores after the anodizing process has been completed. So it is really hard to say whether one particular brand/type is better than another without doing a number of tests.

In principle we feel it that painting on these surfaces would not pose too many risks if the surface is properly prepared. For surfaces that possess polyester coatings (an alternative to anodizing that industry uses to counteract potential corrosion) we recommend degreasing, lightly scuffing the surface to provide tooth, and then applying subsequent layers of primer and paint. We are unsure at this point if lightly sanding the surface of anodized aluminum would be necessary or even a good idea (just as with polyester coatings you do not want to abrade TOO heavily as you risk removing this protective layer entirely). This may very well depend on the thickness of the anodizing layer. But you could certainly ask your manufacturer whether using a 320 grit sandpaper (which is what we recommend for polyester coated ACM…you may need to use a finer or coarser grit depending) would ever get you close to the bare aluminum underneath for a particular brand of anodized aluminum. As for painting directly onto the surface without sanding, again this would require additional tests for any given brand. If the manufacturer states that it is alright and you chose to forego performing any tests yourself then things might work out fine….if not then the manufacturer should not be surprised when they receive an unfortunate phone call from you.

Even though we tend to advise folks to steer clear of most industrial products, sometimes there are certain instances when one actually SHOULD turn to industrial products to ensure the longevity of their work and with ACM this can certainly be the case. DTM Bonding Primer by Sherwin Williams has been tested and found to be a suitable primer for ACM, a primer that can then be covered with a layer of acrylic gesso (followed by acrylic or oil paints).

For piece of mind you can always adhere a canvas to the support first before applying any size/primer, ground, paint, etc. That way should there be any issues in the future the canvas support can be safely removed from the problematic ACM panel and simply re-adhered to another rigid support. There are instructions and additional information relating to this process as well other aspects of ACM that can be found in our "Rigid Supports" document in the Resources section. 

​These are all very good questions...in the sense that they are unanswerable from the point of view of a conservator simply because not enough time has transpired for us to say one way or the other. This is why we tend to lean towards the more "conservative" suggestion of adhering a canvas down first JUST in case there are issues later on down the road. But there very well may not be any problems...in either case do consider recording whatever you choose to do on the back of your panels.
The point of the primer coat is to promote better adhesion...but if tests demonstrate that certain methods are working fine without a primer (I recall that earlier tests using true gesso, meaning animal skin glue, did not pan out and lead to cracking and delamination) then the primer coat may not be necessary for certain layering systems and/or certain types of aluminum substrates. Hopefully some of our other moderators will weigh in on this...I will also try to reach out to some objects conservators who may be able to shed some light as well.

​The last User comment (with time stamp 2017-04-10 23:55:32) would be George O'Hanlon from Natural Pigments...
But I would say "Yes," anodized aluminum is likely fine but we really cant say for sure without doing more testing.