I prefer glass beading because it's easier on the steel,but.Here's my philosophy on etch primer:if you blasted it or sanded the bare steel with 80-150 grit,you really don't need etch primer because the surface is etched very good already.Some etch primers have some zinc in them so it is a slight benefit.I'm a PPG man,so I believe the equivolent is 1790 wash primer.Here's what I do and don't have probs.The surface is pure clean blasted or sanded steel.One coat of DP40 (green).There are about 6 or 7 colors to choose from,but green has the highest zinc content,and white is junk on bare steel.You can use it as a wet on wet sealer or wait an hour and do your mud work (bondo or putty) right over it-much better than over bare steel.I let it sit overnight to a day before I touch it for this reason:it has a window of 1-3 days depending on which hardner you use(also the reason I dislike it as a sealer).What this means is that anytime in that window,you can topcoat it with mud or paint without sanding it-it stays soft a long time.I let it breathe 12-24 hrs before scuffing for mudwork or if it's paintable,I lightly 600 it and let it set another day before sealing it.There might be something better than DP,but I haven't found it.Alot of people snub their nose at this but it can't be said enough-don't mix products or paint lines.If you pick PPG,DuPont,HOK,etc.,stay with their products.There is a touch of room to play,but you have to know what your doing and test it long term,plus it will void any guarrantee the paintline has.
Newbe,I might be off a bit,but someone will clarify if need be.Etch primer will actually etch the metal very finely to give the next product some mechanical adhesion,like sanding it.Great if you chemical strip something and don't want to sand the bare steel-it's hell on a piece of sandpaper.Some (all?) have zinc in them to help prevent rust from forming.I have used them a little,but I can't tell the difference in using it or not.
