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
 
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