Well I think I'm at the point where my 53 needs to be coated with primer. I have stripped the cab to bare metal, welded in new cab corners and driver floor. I added body filler over the bare metal to smooth out the welding repairs. Why did I go with filler over bare metal you ask? It seems the forums are split over primer first then filler or filler then primer. And out of necessity ( I don't own a spray gun yet) it was easier just to continue on with the body work, spread the filler and sand.
I want to spray some epoxy primer over the cab. The cab is random orbital sanded to 60-80 grit. The filler is at about 220 grit. Is that enough bite on the filler for the epoxy primer?
FYI, I will be using either the Summit or Eastwood epoxy primer for budget reasons. The epoxy primer will be followed by any additional filler needed and then highbuild primed. I think I will be going with the satin black look for now but that is subject to change when the time comes.
You should be fine with the prep that you have done. I was not familiar with the Eastwood product so I looked at their website and found out how much this primer cost. At $60 a gallon for the primer and $40 for the catalyst you are in the price range of many quality products. I use SEM Metalock 010 for all my primer needs. Mixed without reducer it is a high-build direct-to-metal (DTM) primer; with half reduction it is a primer surfacer; with full reduction it is a sealer. This primer drys fast and is easy to sand. I pay about $85 at my jobber for the kit...1 gal of primer and 1 qt of catalyst.
As far as the filler over metal goes...many years ago the fillers would not adhere well to anything except bare metal. Today the fillers are formulated to bond very well to primers. The primary reason that you should prime first and then fill is that you are reducing the chances that moisture will get under the filler and spread across the unprimed metal. The filler itself is not porous but if there are any cracks in it or any way that corrosion can get a foothold then there is the chance that the corrosion will spread more easily if the metal was not primed first.
Charlieled is right. In the acrylic enamel and lacquer days of yor the filler would not adhere to the primers. It is easier in my opinion to blast or grind and sand/then fill and form your filler and then epoxy and then high build primer.
I have a relative at ppg so I get some good deals.....but you should be fine with your prep work thusfar.
I've sprayed both Eastwood and Summit. Eastwood's Epoxy primer is pretty good stuff, but the high build primer is like spraying snot. I also shot their red urethane top-coat and then put their clear on top. Considering it was done in my driveway, I'm happy with the results. I only shot Summit's top coat(over Eastwood's Epoxy without issues). I did not like shooting Eastwood's paint as it ran too easily on vertical surfaces. I'm far from a professional painter, but I'd pick Eastwood's over Summit's any day.
Make sure it's as clean as it can possibly be, wipe it down with a good pre-paint cleaner while wearing gloves before you spray. Things like finger prints leave oils, which can cause problems down the line.