I am planning to paint my shed. Could I use some leftover primer as the exterior finish coat? -Aaron
Primer is not formulated to stand up to the elements and should be topcoated within several weeks to ensure proper bonding. If left uncovered for an extended period of time, primer will tend to deteriorate and chalk, which could prevent future coats of paint from adhering properly.
Also, primer comes with a flat sheen to promote bonding between the substrate and top coat, which does not hold up as well to sun, rain, and dirt as satin or glossy paints.
Good luck with your project,