Afterblast

Old school JW

New Member
All, I sand blasted firewall a year ago and wiped Eastwood afterblast on surface to keep it from rusting. It seemed to work fairly well. Now I'm preparing for epoxy and some smoothing. I'll be sanding with #80. Is there anything specific I should do before 700 and 710 wipe to assure surface is clean? Thx
 

Jim C

Oldtimer
yes, that is a zinc coating. it all needs to come off. you really need to blast it again and put it in epoxy. zinc coatings are a bunch of bs. the paint will peel off in sheets if you just wipe with cleaner and spray right on it.
 

crashtech

Combo Man
I would be willing to bet that Ospho would be a viable alternative, IF @Barry agrees and you follow instructions exactly. Zinc phosphate itself is not actually a problem imo, but acid residues from untested products are, and Ospho can remove those. it will also replace the zinc phosphate with dichromate instead, I think.
 

Jim C

Oldtimer
i have not used ospho but if it removes the afterblast then by all means, that would be much easier but you need to rinse off the ospho. if you have bare metal that doesnt rust when it sits out then that is a red flag right there. you know something is on the surface sealing the metal. paint directly over it and your paint is only stuck to this coating or film that is sealing the metal.
 

crashtech

Combo Man
The zinc in AfterBlast is just a thin layer of zinc phosphate, which should be able to be dissolved and washed away by a subsequent application of an acid product like Ospho, which has been tested to work with SPI epoxy if the technique on page 13 of the Tech Manual is followed.

The main problem with acid treatments is that they are often improperly neutralized. An acid film means death to epoxy primer. The technique in the manual is very clear about thorough water rinsing, this is not optional!
 

chevman

Oldtimer
I use a similar product that is phosphoric acid with zinc phosphate then wipe it off for bare metal protection all the time. Keeps it from rusting for well over a year, maybe a lot more, just depends on your environment. I always keep my shop heated, but the summer can be worse if you have a well insulated shop. Cool shop, hot humid air outside, and when you open the door the humid air will come in and condense on the cool metal.

To remove the zinc phosphate it just takes a reapplication and keep it wet long enough to wake up the first application, then it can be rinsed off. I like to keep it thoroughly wet for about 15 minutes, then use a red scotch pad wet with the acid to scrub it before rinsing. It also gets all the loose carbon off and leaves a really clean surface. You still have to do a 80 grit DA scratch though. Eastwood gives some bad info in their video.
 
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Barry

Paint Fanatic
Staff member
Just went through this for a guy this week, it has phosphoric acid in it, so he bought ospho to treat it and neutralize it.
Never paint over an unneutralized acid.
 

Old school JW

New Member
Thx. Got Osphos. Spray bottle wetted. Waited. Wetted and scrubbed with brush and red scotchbrite. Wiped. Squirted with water and scrubbed with different scotchbrite. Rinsed and wiped dry and air gun. Some extra water came from seams. So wetted with Osphos again and went through same process again. Seams seemed cleaner second time with air. See pic. Does this look about right for proceeding to # 80 and 710 wipe and dry before epoxy. Slight surface rust toward bottom. Does that need to be removed completely with sanding? Thx to all.
IMG_20200725_084158025.jpg
 

elskeptico

New Member
Never paint over an unneutralized acid.
Barry - I've seen and appreciated your many posts about neutralizing ospho before putting anything over it. I have a question about timing with regards to neutralizing. Is it important to neutralize just before painting or coating with epoxy, or is the timing irrelevant? Let's say I used ospho on a section and the next day I neutralized it (using your method), but then didn't coat it for another couple of months? Would I need to neutralize it again just before coating? Thanks!
 

Chris_Hamilton

Trying to be the best me, I can be
Barry - I've seen and appreciated your many posts about neutralizing ospho before putting anything over it. I have a question about timing with regards to neutralizing. Is it important to neutralize just before painting or coating with epoxy, or is the timing irrelevant? Let's say I used ospho on a section and the next day I neutralized it (using your method), but then didn't coat it for another couple of months? Would I need to neutralize it again just before coating? Thanks!
Not sure from reading your post so I'll mention that "neutralizing" ospho or other phosphoric acid treatments, means re-wetting your work with Ospho and then rinsing off with water while the Ospho is still wet. If it dries you need to make sure you re-wet it, then rinse.
 

elskeptico

New Member
Thanks guys. I think I understand now the purpose of neutralizing. If it dries it leaves a film and the only way to get it off is to re-wet it with more ospho, then rinse thoroughly with water and then no more acid film. This has probably been said various ways but I wasn't quite getting it until now :rolleyes:
 

crashtech

Combo Man
Can I add that leaving stuff in bare metal for long periods of time is just not the best practice? Strip the area, do the metalwork, then prime it. Don't strip more than you can handle within a short time frame. That way, you don't have to worry as much about contamination and corrosion.
 

elskeptico

New Member
So, in my case, the reason I'm planning to wait on priming is that most of the areas need filler and I understand the filler will bond with the epoxy primer better if it's done within 7 days of priming. But maybe my priorities are off. Maybe I should prime as I go as you suggest, then when I'm ready to do filler, sand the cured epoxy primer first? Or sand the primer and shoot another epoxy coat and then do filler?
 

crashtech

Combo Man
I can only speak to the way we do things, which is to do metalwork, prime, fill, then prime again. One or two panels at a time, maximum. Once all the panels are done this way, larger numbers of panels can be blocked and primed to get ready for paint, but having large amounts of bare metal remain unprimed for long periods of time is something we never do.
 

crashtech

Combo Man
I guess I wanted to add that we do sometimes have large amounts of blasted metal around, in that case we prime it all immediately without worrying about metalwork. That way, metalwork can proceed at any pace without worrying about contamination and corrosion.
 
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