Your foundation is the most important step for any project or repair.
HP-5310 builds like a polyester, is a true direct to metal, doesn't crack, won't shrink on sand scratches, is easy to sand, can be "value shaded", and can be used as a sealer (when reduced).
This primer has a perfect amount of flexibility built in. It's not brittle or prone to cracking (like poly filler "primers" are).
This primer will not shrink. It's 65% solids. Builds like crazy, can be sanded in as soon as 45 minutes. Blocks like butter! Temperatures come into play with sanding times.
This primer should be topcoated within 2-3 months.
Do not leave it in the elements unprotected, store inside only.
It's extremely thick. Most spray reduced at about 10% with a urethane reducer. If spraying 4:1 use a 2-2.2 tip no reducer.