I agree with dadiOH and haven't sanded paint finishes past 220 in years. If you are sanding correctly, you simply don't serve any purpose in doing so unless that suits your personal taste. I would say that 99% of people sand way too much anyway to make up for woodworking deficiencies, poor finishing, and for some reason it seems to make some folks feel like they are connecting to "fine woodworking" when they get to the sanding stage.

As far as sanding latex, I don't know any professionals that sand latex unless they are correcting the incidents listed above. It isn't necessary, and I have even gone weeks between coats and had no adhesion problems. Latex by nature is a porous finish and subsequent coats will adhere just fine. Stay with the same product and there won't be problems.

I like the idea of changing to alkyd finishes. If I can, I apply those.

If I have to prime, I like BIN over all other products. No thinning needed, you can put it on whisper thin, shoot it with the same tip (I use 1.2mm) that you use to shoot finish, and it doesn't foul the guns. Plus... it just works.

But Len, if you are in "production mode", why are you priming? Most of the time it adds nothing to the finish if you are starting with new moldings, trims, doors, shelving, plywood, etc. Priming is a good idea if you are painting dirty wood, over old finishes, or painting over contaminated finishes. It is also a good idea if you are painting over finishes in areas that have had a lot of cleaning such as in kitchens, baths, etc., where spray cleaners and soapy products or other chemicals might leech into your new finish.

If you are coating new materials, use the same paint you are using for finish as the primer, mid and top coats. NOTHING sticks to a finish like itself as it is specifically formulated by the manufacturer to do just that.

Put the sandpaper away, ditch the primer, and keep the Impervo. That is some really good stuff. I have only used it on one job but shot a lot of it, and it was like shooting liquid plastic. Shot clean, required little thinning in my pressure sprayer but none in my airless, and the finish tightened up to a glassy smooth finish when applied at 3 mil for the first two coats, then a bit thinner on the last.

I think in "production mode" you should load your gun and start shooting.

Robert