Have a glass blasted car in for paint. Needed to apply Ospho for surface light rust that developed. We are trying to determine how to neutralize before epoxy primer goes on.
Instructions say brush off dry powder then wipe with mineral spirits. In another section it says to etch wet with Ospho for 30 minutes then wash down with water.
That seems risky due to flash rust.
Anyone have experience to recommend which way to go.
TIA
Terry

Ospho website says apply thin coat and let dry 24h before applying paint.

http://www.ospho.com/directions.htm

Older bottles of Ospho I bought said to neutralize with water or mineral spirits, but the last bottles I bought just said to let it dry. I found spraying with water and wiping with a damp rag worked best (see the etching clean metal instructions in the link
@Montreal914 posted). When the Ospho coating is wetted with water, it develops a phosphorous powder coating. I removed the powder with a red scotch bright pad which left a smooth, etched surface. Just letting it dry sometimes left an uneven coating and I still worried about not neutralizing. Just try a small area with water and see how it goes. I didn't have any trouble with flash rust. In fact, after Ospho treatment I left the car bare in our dry climate for months and still no rust.

Personally, I belieive it needs to be neutralized. Go look at the various technical literature for your specific paint - don't belive me. Don't belive others opinions.

Ospho is not really designed for use under automotive finishes, especially 2K which doesn't like an acidic base metal that will be left by Ospho. I've never found it referenced by name in paint technical info. Ospho is basically designed for industrial and/or structural use with an acrylic enamel topcoat - I belive that is where their instruction to let it dry come from.

All I can tell you with certainty is that base surface prep is critical to paint success. Read and understand your paints technical literature. Failure to do so can lead to complete delamination of the paint.

Having said that, guys have been using vinegar and light acids to clear rust on project cars for decades including as prep for 2K. However, it was always advisable to neutralize the acid before paint.

The way you prevent flash rust is to work a small area to neutralize it and then IMMEDIATELY blow the water off with compressed air. This will prevent the flash rust. Brent's methold above of only working small areas with damp rag and scothbrite will achive the same result. Get it on, get it off and dried before the yellow flash rust develops.

SPI is not PPG, DuPont, or BASF but they do support the hobby more than the big guys. As stated previously -- read YOUR tech info but thought I'd post this link from SPI regarding Ospho.
http://www.spiuserforum.com/index.php?thre...ize-ospho.3973/

That link about SPI is a good one and covers some things I didn't, like reactivating dry Ospho coat by rewetting with itself before neutralizing.

I'm not sure what Ospho was designed for, but it is labeled for etching bare metal for primer prep by following a different procedure that includes neutralizing. Also, PPG doesn't seem to mention any other products other than their own by name, but the directions for their DPLF epoxy primer include this: "Chemical treatment or the use of a conversion coating will enhance the adhesion and performance properties of the finished system."

Lastly, I think Ospho (and other phosporic acid treatments) is different from mild acids like vinegar in that it forms a dry phosphorous coating after wetting with water which reduces the tendency to flash. It was a non-issue in my Montana climate but I notice OP is in Florida so YMMV.

Being in the midwest with 80-90% RH in summers, I fight flash rust on everything from sheetmetal to my machine tools.

Dehumidifier in garage has really helped. My garage isn't tightly sealed by any stretch. Can usually keep it down to 60% RH which really reduces flash rust potential.

Mar Hyde is a good alternative to Ospho for rust conversion. Most auto body supply outfits carry it. Or did. More exspensive tho. Clean and dampen surface with water, paint the surface with the MH, paint again, and finish as required.

Whatever you do, USE EYE PROTECTION when using Ospho!!! Ask me how I know.
Goggles not safety glasses.

Ansbacher

Appreciate all the input but stills concerns me.
I called Ospho tech assistant line. Neutralizing with water only if you are etching new metal. If rust then let it dry and wipe with mineral spirits.
I Noted that it said test if using epoxy primer…..and we are.
They said not always but has been issue which means it could be.
Finally he advised to use metal etching primer and then use epoxy.
Anyone want to comment further is certainly welcome.
All of this rattles me as don’t need any experiments or disasters as you can well understand.
Thanks again

Pick a paint line that you want to use and can get help locally or thru phone. Use what they list on the tds and how they tell you to use it.

Great info

Thanks !


quote name='Superhawk996' date='Oct 6 2021, 04:03 AM' post='2950645']
[quote name='Montreal914' post='2950598' date='Oct 5 2021, 11:03 PM']
Ospho website says apply thin coat and let dry 24h before applying paint.

http://www.ospho.com/directions.htm
[/quote]

Personally, I belieive it needs to be neutralized. Go look at the various technical literature for your specific paint - don't belive me. Don't belive others opinions.

Ospho is not really designed for use under automotive finishes, especially 2K which doesn't like an acidic base metal that will be left by Ospho. I've never found it referenced by name in paint technical info. Ospho is basically designed for industrial and/or structural use with an acrylic enamel topcoat - I belive that is where their instruction to let it dry come from.

All I can tell you with certainty is that base surface prep is critical to paint success. Read and understand your paints technical literature. Failure to do so can lead to complete delamination of the paint.

Having said that, guys have been using vinegar and light acids to clear rust on project cars for decades including as prep for 2K. However, it was always advisable to neutralize the acid before paint.

The way you prevent flash rust is to work a small area to neutralize it and then IMMEDIATELY blow the water off with compressed air. This will prevent the flash rust. Brent's methold above of only working small areas with damp rag and scothbrite will achive the same result. Get it on, get it off and dried before the yellow flash rust develops.

SPI is not PPG, DuPont, or BASF but they do support the hobby more than the big guys. As stated previously -- read YOUR tech info but thought I'd post this link from SPI regarding Ospho.
http://www.spiuserforum.com/index.php?thre...ize-ospho.3973/
[/quote]

This is different, but the same reason why most companies don't recommend soda blasting.

Not sure what brand of epoxy you are spraying, but I can tell you that PPG DPLF epoxy sticks like stink on a monkey to properly Ospho prepped metal.