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Metal Prep Question Prior to Epoxy.

#1
Not sure this is the appropriate place to put this but I'm hopeful that it will fit in. I've stripped my car to bare metal with plastic media, cleaned it with SPI cleaner, and DA'd it with 80 grit. It's ready to prime with epoxy. My concern is an area on the roof that I guess is residual rust. I've sanded the roof with 80 grit and this is what I get.....see photos. Not sure I want to sand on it much more. Would I be okay to go ahead and shoot epoxy over this or should it be treated with something prior to the epoxy? Thanks!
 

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Barry

Paint Fanatic
Staff member
#2
From what i see we need to treat with
Some ospho and help it with a wire brush.
Looks like to big a gamble to epoxy.
 
#3
I personally wouldn't shoot epoxy over that. IMO really needs to be blasted with something more aggressive than plastic to get down in those pits. Those look to be too deep for Ospho. (Barry was too quick for my hunt and peck):)
 
#4
Ok, but I've been trying to do my homework and found this:*Never use a rust converter of any kind. NO MATTER WHAT IT IS.

Isn't Ospho a rust converter?
 
#6
Here I go again, jumping in where I don't belong. :)

If you are going to use Ospho, the key is to neutralize it well. rinse with lots of water and NEVER let the Ospho dry.

Personally, I like to use the Ospho mixed with sand blast media scrubbing it into the pit until they are bare metal. It may take numerous applications but you will know the rust is gone and NOT converted when you can scratch the bottom of the black rust pits and not uncover brown residual rust. Use a scribe or similar pointed object to verify the rust has actually been removed.

Again, be sure you get all the acid removed with lots of water. It won't hurt if you dry the car when you are done. I have a '36 Ford roadster right now that has blisters in the paint that may be caused by residual acid left on the surface.

John
 
#7
Here I go again, jumping in where I don't belong. :)

If you are going to use Ospho, the key is to neutralize it well. rinse with lots of water and NEVER let the Ospho dry.

Personally, I like to use the Ospho mixed with sand blast media scrubbing it into the pit until they are bare metal. It may take numerous applications but you will know the rust is gone and NOT converted when you can scratch the bottom of the black rust pits and not uncover brown residual rust. Use a scribe or similar pointed object to verify the rust has actually been removed.

Again, be sure you get all the acid removed with lots of water. It won't hurt if you dry the car when you are done. I have a '36 Ford roadster right now that has blisters in the paint that may be caused by residual acid left on the surface.

John
Thank for jumping in, John.
 
#9
Hey fellas, thanks for the responses. Regarding the neutralization process of Ospho, I've read just water and also soapy water. I don't want to screw this up. Would I be find neutralizing with just water or soapy water? If soapy water, what product in the water?
 
#11
Ospho is formulated to leave a film after rinsing for rust protection, so when you are ready to rinse, you will get a cleaner rinse if you apply fresh ospho then use a red scotch pad to scrub the panel good to get all the acid in suspension before rinsing. Then its important to dry quickly and do a DA scratch and prime right away to prevent flash rust.
 
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#12
Hey fellas, thanks for your input here, very much appreciated. I spent about 4.5 hours removing the rust shown in the above and previously attached photos. I used Ospho and a combination of wire wheels. I then rinsed with water and a scotch bright pad three times to ensure complete removal of the Ospho. This was not a fun job! Also, in the rinse, I was amazed at how fast flash rust would appear. I'm talking minutes. Last rinse, I dried her off, cleaned with SPI cleaner and DA'd with 80 grit. She sports a couple coats of SPI epoxy now. Thank you, Gentlemen!!! Car Roof 1.png Car Roof 3.png
 
#13
What is crazy to me is putting epoxy over flash rust, then sanding through the epoxy a couple days later and the metal is snow white clean. Where did the flash rust go?
 
#14
I then rinsed with water and a scotch bright pad three times to ensure complete removal of the Ospho. This was not a fun job! Also, in the rinse, I was amazed at how fast flash rust would appear. I'm talking minutes.
You left it wet too long. If you do the scotch pad scrubbing on the wet acid before starting to rinse, then when its ready all you have to do is rinse and dry. But you will still need to get it in epoxy the same day because you will have removed the zinc phosphate.
 
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