Internal cavity rust treatment, Would/do you use Ospho? Options

[bbrock]

This question is specifically for those enclosed cavities that do not get opened during a full rustoration. On my car, there aren't many (inner cavities of roof pillars, roll bar, windshield frame, trunk cross member, and inside driver's suspension console). I bought a bunch of tubing to modify a garden pump sprayer so I could spray Ospho/Jasco inside those cavities. My thinking is that it would seep into seams where there is ALWAYS rust even in parts in good condition, and convert whatever rust it contacts. This would be followed by treating with Eastwood Internal Frame Coating, and finally, 3M Cavity Wax Plus. So two questions about the Ospho treatment:

1. Would you do it? It makes sense in my head, but it is spraying acid inside structural components.

2. If you did, would you follow with a water spray to neutralize the acid? My understanding is that the product forms a protective coating that can be left indefinitely, but it needs to be neutralized before it can be painted. For internals, I wonder if I'd get better long-term protection by just spraying Ospho and leaving it alone.

Thoughts?

[Rand]

Yes I'd use Ospho. No I wouldn't rinse with water.

[marksteinhilber]

Yes I'd use Ospho. No I wouldn't rinse with water.

I use OSPHO and will rinse it on extrernal body parts where I can dry it immediately thereafter. Then epoxy primer. If I use it internally, I make sure that I can drain it and if I can, will also try to rinse it and drain that. If any black oxide remains, I use POR 15 preferably, but also use other spray rust converter or encapsulator, then primer. The internal frame spray primers are sold for the convenience of the hose and spray head that it comes with so you can coat way up inside the longitudinals or even the center tunnel on our cars. I have had very good success with POR15 on floor pans when I remove enough scale and rust powder and follow the directions. It needs topcoat as it is not UV stable.

Some discussions are concerned with remaining acid between layers of metal. If these are re-wetted over the years from rain, this could reactivate the acid and etch or remove more steel. There is merit to this concern. If used, flushing and good drying is needed before rust conversion or sealing with epoxy primer.