Painting defect cause?

the caliper paint is great in specific applications (calipers!) but it dries rock hard and any kind of flex what so ever and it'll crack and chip out.

like harrison said, you're likely having compatibility problems between the products and that's only compounded by poor prep and unfavorable application conditions.

if you're looking for a matte black that's durable, sprays easy, covers well and is forgiving look at chassis paints. yeah, yeah, i know they're $25 a can but you get what you pay for.

or hit it with some rustoleum bbq black and wax it. presto soft matte and you can touch it up!