: Look for the 4-in-1 formulations to skip the primer stage on tricky surfaces like aluminum or brass.
Since "U90" is often associated with industrial standards (specifically the USS U-90 submarine specifications or generic industrial undercoats) or architectural color systems, this guide assumes a hybrid approach suitable for a professional paint brand. You can adapt the specifics based on whether this is for industrial, automotive, or decorative use. u90 paint catalogue