TheSamba.com :: View topic

Sun Jun 14, 2015 6:15 am

I have been doing some work on the '74 and am curious how others have proceeded with rust treatment.

I have welded in my new battery box plate and was able to do so without destroying the paint on the outside curve. All of the metal now has been stripped of paint, ground or sanded. I'm about to treat the entire area with Ospho and apply Masterseries rust treatment.

Ospho directions and all I've read says that the Ospho attaches to the surface rust to form an iron phosphate surface for painting. Since a lot of the area on my repair is bright or sanded metal and does not have any surface rust, I'm not sure if I should just go ahead and treat with the Ospho and Masterseries or if I should just drive it for a while and wait until the surface rust forms and then continue with the Ospho and Masterseries then epoxy primer and paint.

What should I do here?

Sun Jun 14, 2015 7:00 am

A couple different ways to look at it.

The bluish white film that ospho leaves on bare not is not a bad primer but its not anywhere near as good of a primer as the converted iron phosphate.

I dont know what the Ospho directions read like these days.....but back about 10-15 years it noted that on bright unrusted metal.....after the conversion has dried completely and the rust patches are black......clean the whole thing with acetone or another fast evaporation, clean solvent to remove the bluish coating on the bright metal.

The other way and is a great way to go.....is to grind or sand the crusty areas down to thin ragged rusty areas......lets see how to explain this....

The real use for me more ospho is to convert areas that you just cannot fully reach...crevices....wide spread below surface pits with rust you cannout reach by sanding etc. The object is to get these areas down to a thickness of a few thousandths of an inch of rust so that the ospho can convert it all the way through.
Encapsulating thifk rust....is not effective.

So take as much of the rust off as you can reach. Then solvent wipe to open things up......then wash with soap and water. This will within about 24 hours...promote widespread, very thin and fairly even flash rusting of the surface.

An even better method but not for the lazy or faint of heart........is to take some 50/50 muriatic acid and water....and wipe the whole panel surface. This will help dissolve even more of the rust in the pits and crevices......and then rinse well brushing into the crevices and pits with a soft brush. Dont neutralize this with baking soda and water.

Its not the same issue as if you were using very high solution strength muriatic acid to dissolve very thick rust.....and then needing to neutralize it.

This use of muriatic acid and water as a wipe and then with a very complete rinse......will promote very widespread flash rusting.....which is perfect for ospho to convert.

Once the whole surface has been treated with ospho and dried for 24 hours.....it will feel rough as it blooms outward a little from the pits. A very light once over with something like 280 grit.....is good to even the surface. If this once over reveals red rust in the dust it leaves....the rust was too thick somehwere for ospho to penetrate fully. Give it another thin once over with ospho kn a sponge....avoid making foamy areas. ...wipe them level. Let dry......quick once over again with medium sandpaper....tack it off.....and spray yoir priker onto it. Ray

Sun Jun 14, 2015 7:03 am

How did you weld in a battery tray without burning the paint on the outside?

Sun Jun 14, 2015 7:39 am

Fortunately the tray was not rusted all the way to the skin but retained a +/- 10mm rim to which I welded a plate. I used a product called "Heat Fence" to stop heat transfer to the skin. Worked.

Ray- Why does the Muriatic Acid done 50/50 with water not need to be neutralized? I have some places that I can't reach and I like the idea of being able to stop the rust action here.

Also I have some rust inside the area behind the pie plate in front of the battery tray area. Any suggestion how to deal with this? it won't be possible to paint this area.

Sun Jun 14, 2015 11:18 am

Lil' Lulu wrote: Fortunately the tray was not rusted all the way to the skin but retained a +/- 10mm rim to which I welded a plate. I used a product called "Heat Fence" to stop heat transfer to the skin. Worked.

Ray- Why does the Muriatic Acid done 50/50 with water not need to be neutralized? I have some places that I can't reach and I like the idea of being able to stop the rust action here.

Also I have some rust inside the area behind the pie plate in front of the battery tray area. Any suggestion how to deal with this? it won't be possible to paint this area.

In places where large amounts of water spray cannot reach...like say...heater channels and body tunnel....places you cannot lay your eyes on....DO neutralize it....because you can never be sure that you rinsed it really really well.

I am speaking of external body and underneath the body pan where you can see what you are doing and reach these areas with the water spray.

You will get some surface rusting after neutralization because there is some sodium that splits out of the sodium bicarbonate after you add it with water....but usually I am rinsing that away as fast as possible.

The reason it is nice to not neutralize after muriatic acid usage....where you can....is that you get some hydrogen embrittlement of the surface of the metal from the acid...which promotes rust. So if the whole surface is treated...you get a really fast, very thin flash rust....perfect for phosphoric acid.

In areas like body tunnels and heater channels.....I recommend Jasco metal prep and prime rather than Ospho.

It is phosphoric acid based....but is about 2.5 to 3X stronger than Ospho. It can and will do some deep eating of thick rust similar to muriatic acid...but leaves a bluish/whitish residue similar to ospho that is MUCH MUCH harder to remove. For outside body panel use I would dilute it as the directions note you can.

Put it into the heater channels and get a long rod with a gun cleaning brush and work it into crevices. Let it dry. You will see it fizzing and foaming in rust areas. Do not get it on important platings you want to keep.

let it dry overnight and repeat. You will be dead before the heater channels and tunnels beginnb rusting from the inside out again. Ray