Etch Primers Supplied as primer base plus activator, to be mixed before use. Provides maximum adhesion to bare metal and better corrosion resistance. Absolutely essential for aluminium or galvanized steel. The activator is usually phosphoric acid based, therefore do not store activator or mixed primer in metal tins. The useful life once mixed is about 48hrs. There are two general types available;
Etch Primer-Fillers have moderate filling properties similar to cellulose primers, and are applied in two or three wet coats, leaving 10 - 20 mins between coats to allow solvent to evaporate. Suitable for minor filling uses, or can be overcoated with cellulose or 2-pack primers.
Wash Primers, that is, with no filling properties at all, are usually applied as one single wet coat over all bare metal areas. These are used simply for maximum adhesion and must be overcoated with cellulose, 2-pack or synthetic primer filler to achieve the required build and moisture protection.
If any etch primer is used under a conventional primer filler, then one single wet coat is sufficient The etch coat must be dry (resistant to a light fingernail scratch) before continuing with either primer filler or paint.
Etch primers are sensitive to moisture, so must NOT be left for more than a couple of hours without either primer-filler or paint being applied.
