Fek, arse, bollocks.

Undersealed my rear end (oh err) last week, and just re-inspected, its pulling apart at corners and seams.

I used Epoxy mastic 121, which worked fine, then Dinitrol 447 grey rubberised. Didn't get a great thickness, 3 tins not enough. Normal shutz gun at about 75psi.

Any ideas what I did wrong?

Looks like it's gone on to thick and shrunk to me... though as to how long that stuff needs between coats is anyones guess! I've certainly seen factory stuff with similar cracks in it, maybe another thin (hah, like thats possible) coat now?

I thought it was on pretty thin, the big lumps BTW are welding. The big vertical seams in the wheel arch are really bad aswell and I used and fair bit extra there. Maybe you need to brush it in there?