I've stripped this hood down and found large sections of black and brown rust under the paint. .
The underside of the hood is much worse with large crusty flaky rust
I am concerned about sand blasting this due to how large and flat it is.

How should proceed to get this ready for epoxy primer?

 

Take some 80-100 grit on a DA and sand down to get into the pitting. Then clean it and put a mask on, spray OSPHO on it liberally and with gloves on scrub it into the metal with a scotch pad. Wipe it off real good, dust with OSPHO spray and leave it over night. Next day neutralize the acid by spraying a light coat of Ospho on and scrub it down wo\ith water. get your epoxy primer on as soon as it’s good and dry. You can take it and have it soda blasted too, I have used the Ospho method for years with excellent results
Ospho is phosphoric acid with metal conditioners in it.

 

Andy,

Thanks, Ive been reading on the ospho process and wasn't ready to give it a shot. Its good to hear that it has worked for you. It seems the most important step is re-wetting it with more ospho before cleaning..

I'll let you know how it turns out.

 

That doesn't look too bad. What's the bottom look like?

You can always use 80 grit sandpaper to remove the rust. Then use wax remover/degreaser and spray your epoxy primer.

 

yea, reset, scrub clean and dry then epoxy. It will be fine..just use your DA to sand deep into those pitting areas. Don’t overheat the metal with the sanding process. It looks like a fair amount of pitting so use 2-3 coats of a good epoxy build primer..I USE PPG 2050 HIGH BUILD, NOT CHEAP BUT GOOD ****..Best to you.

 

this is the underside...

 

That is worse but not cancerous.

x2 on using the chemical rust neutralizer. You guys are quicker on the draw than I am.

 

Ive used phosphoric acid before on a frame, but it was just the home depot prep and etch. I never tried real paint over it, and to be honest i never mixed it right. I definitely wont try that under the primer but reading the ospho procedures it all makes much more sense. I dont think i was ever cleaning it properly

 

The underside of that hood may be best if you get it soda or media blasted, that’s pretty crusty.. if you don’t then wire wheel the crap out of it and then follow the same procedure as the top side as explained.

 

I haven found soda or media to remove rust satisfactorily. And yes, it's a delicate process to sandblast, so I don't like recommending that. As for acid scrubbing, that's my choice. I use phosphoric acid, sometimes available as concrete cleaner in the box stores. I prefer to dilute it a bit, scrub the metal with a Scotchbrite pad. Rinse and evaluate. I do it until ALL the dark material in the pits is gone. The dark stuff is still rust deep down. Once it's all "white metal" you need to neutralize the rust, esp. if using epoxy. Rinse with plain water, a couple times, spray with air, and then spray it with alcohol, to remove any stray water, and prevent flash rusting.
It's super important to get rid of any residual acid, as epoxy does not like to go over a surface treated with it. It may go on nice, but adhesion will suffer, to the point of peeling off later in it's life.

 

before sanding I make sure panel is 100% oil and grease free otherwise you just grind it into the panel. Dawn soap and water and wax and grease remover to be sure... after phospho trreatment , yes scrub it down with water and ASAP use lint free paper towels and blow off completely dry I've even run a heat gun on rusty bad areas to make sure it is 100% dry in the pitting areas. and epoxy paint asap later rough up epoxy primer and fill pits with a quality two part glazing putty or polyester primer surfacer depending on how bad the pitting is.

Fred

 

Fred. I’ll definately clean it first I have some wax and grease remover here


i messed with it some last night and I think the black areas I’m seeing may be paint/primer that got hot. It’s not gummy to the touch or anything but it kinda smells like paint when I go after it.

I used the Eastwood Sct drum tool with a stripping drum to take it down to where it is now and I have not used that before. So that could be related to the black areas

the brown is definately rust

 

Here’s the Ospho process…I think I hit it twice with the Ospho and a scotchbrite pad…let it soak in.