They recommend the first two coats over metal be full strength, following coats can be reduced up to 50% for a smoother finish/less peel. I use it full strength and if I have any left over thats four days old I add a shot of reducer to start my 5 day window over. Mostly now I just mix what I need but early on when I was stripping and getting things sealed back up it was handy to have a batch ready to go. Plus it makes nice hockey pucks if you leave an inch or so in a jar for a month!
