Temporary Primer / Paint system for sandblast then weld then later paint

I have to do a pass of sandblasting on the exterior of my (likely corten) steel hull to find and then repair damage via welding. I will be doing this in sections, with some weeks in between sessions. There may be areas I sandblast and leave for a while before I weld it closed. Should I just primer everything after sandblasting, even if I will then come back, grind off the primer, then weld my repairs? I haven't settled on an epoxy paint system yet, so I am not sure what primer I should be using. Does the specific primer matter or can I use a generic primer to cover after sandblasting. I know I should really chose an epoxy system before I do anything, but I am a bit daunted by making that choice correctly. Any help would be great.

 

You should sandblast after welding for better paint adhesion. If you are repairing sections that are corroded, an ultrasonic thickness tester can identify the areas. You can then only sandblast those areas for repair.

 

I concur with gonzo.

If the hull is corten, then just blast with walnut shells to remove the paint in the immediate area prior to the repair and wait to do a cutting grit blast to "clean metal" prior to paint. It won't rust more than a blush. Remember, corten has the anodic protection in the interstitials already...which is why paint voids (i.e. "holidays") can activate it if using a zinc-chromate or zinc-phosphate wash.

Here is a test, blast a small area with an cutting grit to bright metal, then wet with a 50/50 water/isopropyl mix and let dry. If you get an immediate rust blush, you might want to think about a wash, otherwise you won't need it.

 

Good suggestions on this already given. For your work style, the primer I would suggest is zinc-rich epoxy with a long re-coat interval (many weeks at normal temperature). The long interval allows the next coat to go on with no further prep (unless contaminated).

Another approach is to spray on a thin zinc primer immediately after blasting. Then plan on a light sweep blast to remove that coating back to white metal before your final coating system. It is preferred to never allow the steel to flash rust, despite what some sales people may say. This would give the best assurance of a good quality job.

I prefer to paint any steel as fast as recoat intervals allow, keeping a sure chemical hook between coats. This is always how commercial boats are painted.

Best luck in the messy job