The expanding foam will either hold in heat or keep it out. I understood the substrate to be aluminum and the goal is to transfer the heat from the substrate. More details on what you need the coating to do would be appreciated. The ceramic fillers will provide the durability you desire and act...
There are several ceramic filled products out there that do exactly what you describe. Do a search for ceramic filled heat resistant coating, you may find a few to test in you application.
Step 1 - REMOVE THE SALT!!!
Then remove as much of the coating as possible. Abrasive blast to near white metal if you can, then re-clean the surface.
Apply a coat 2+ mils thick [enough to fill the profile and cover the peaks by at least a 1/2 mil] high quality polyamide epoxy that is surface...