Acid Etch? Quick Question

[PyroSparks911]

Me again, before anyone yells at me I will have you know I have searched the forum and found some answers but not all. As you know my car has been sand blasted. I took it to a body shop and the man told me i needed to:

1.Apply an acid etcher, something like the OSPHO product

2.Sand the car with a 120-150 grit paper to remove embedded sand in metal

to smooth it out

3.Then apply epoxy primer to seal car

Does this seam accurate to you? I may have mixed these steps up so clarification would be nice. And yes the bodyman i spoke with is very good. He demonstrated the sanding on a 1968 Shelby KR500, so he knows his stuff.

Thanks!

PS-Any suggestions would be nice, and how long would sanding by hand take?

[26th-Z]

OSPHO is a very mild (15%) solution of phosphoric acid and is considered an "encapsulator" product. Paint applications can be made over it. It will etch the metal and seal the surface from what is called flash rusting - typical after sand blasting. Your body man is correct. It should take you about a day to sand and metal prep the car for spraying primer. Sand the car lightly, spray on the OSPHO and let it dry, then wipe the car down before you primer.

[Mr Camouflage]

Yep sound right. I use that rust converter stuff on all the pannels i strip. Its just phosphoric acid. After its dried i hit it with the wire wheel attachment in my angle grinder.

[26th-Z]

Phosphoric acids will eat metal, but a light solution like OSPHO is readily used for painted metal applications. The phosphoric acids turn ferrous ions into some inert, usually black looking, material. I have soaked rusted metal in OSPHO for long periods and it will eventually eat right down to the bare metal. Wipe off all the excess and let it dry.

Technically, bare metal will start to rust the second it is exposed to the atmosphere. OSPHO treats and seals the metal from those moments. I have heard of "metal ready" and think it is the same stuff. Use a good, high, quality etching primer within 24 hours and you have done about the best you can do.

[PyroSparks911]

Do I sand first, apply OPSHO, then exopy primer OR Do I apply OPSHO, sand, then epoxy?

[26th-Z]

Sand, OSPHO, primer

[PyroSparks911]

Thanks 26th, I went to the hardward store today to see if they carry OSPHO. They did not carry it but they did have a phosporic acid metal primer, same color as OSPHO, called Jasco I beleive. I think it should do the same thing??? Anyways I am planing on using my 6 inch oribital sander to tackle the sanding, with a 120 grit paper. Before I apply the metal primer acid stuff will I need to clean the car off and remove the dust, etc, caused by sanding? Thanks

[ChrisA]

Before I apply the metal primer acid stuff will I need to clean the car off and remove the dust, etc, caused by sanding? Thanks

I would wipe the car down with tack cloths myself, then put on your metal prep solution. Then tack the car again before you put primer on as well. The cleaner the surface the better the end result will be.

I use PPG DX440 Ditz-O wax and grease remover. Put some on a rag and wipe the area you want to prep

My .02

Chris

[EScanlon]

... wipe the car down with tack cloths..... Then ...again before..primer.... The cleaner the surface the better the end result will be.

I use PPG DX440 Ditz-O wax and grease remover. Put some on a rag and wipe the area you want to prep

My .02

Chris

Chris, not arguing since bodyworking and paint prep work are as individual as can be but....

I don't know that I would use the Tack Cloth. Especially on bare metal that's about to be etched. Tack Cloths typically have this icky sticky coating that "traps" all the dust that they come in contact with. Unfortunately most people either just very so lightly drape and wipe or get in there and really scrub it in hard. In the first case, they will just use up a tack cloth and not really get the dirt removed because they didn't apply pressure. In the second, they will smear some of that sticky goop onto the metal surface and cause problems with that.

I would just use a lint-free and non-shedding cloth to wipe the whole car with the Ditz-O W&G Remover using the "Wax-On, Wax-Off" method. (I.e. one hand applies with separate rag, the other removes with separate rag.)

Now, once you get past the etch and epoxy primer, then use your tack-cloths to ensure a blemish free foundation for the paint, but I think it's a bit of an overkill for the base etching primer.

As far as sanding the whole car if, as I understand it, you've sandblasted the whole car; I don't know that I would use 120 grit paper. To me that would be a bit coarse for bare metal work going to etch/primer. You'd almost be guaranteeing that you would have to apply at least one heavy or two medium coats of fill-primer just to get a smooth surface again.

If your metal is straight, and you don't have areas that need bodywork or bumping or new metal going in, then go with 180 to 220 grit for the work after the sandblasting, then do the etch. I've personally never heard of having to sand after the etch, and in my opinion, kind of defeats the purpose of the etch in the first place. But, if that's what you guys know from talking to the paint reps, then do it. Back in "my day", we always shot self-etching primer onto bare metal, so we didn't have a separate etch process.

FWIW

Enrique

[ChrisA]

Thanks Enrique, you're right on, tack cloths can either help or harm. I knew you'd chime in on this thread, you the Master!!!

Chris

[260DET]

We were taught to do the prep work, apply the phosphoric acid solution, let it dry, then hit it with your primer or whatever coat you are putting on first.

Touching the bare metal with anything after the solution had dried was a nono.

[26th-Z]

Thanks for your suggestions, Enrique. If the car was sandblasted, 120 is a little harsh. And I would hand sand the car as I think the orbital is a little rough also. I am also assuming that there is no metal work involved and it is ready to prepare for paint? Sand it down with 220 - 400 grit using long strokes as though you were seriously wiping the car down. Sand it as though you were polishing it. Vacumn the dust out of the car with a brush. Wipe the car down with OSPHO as though it was a cleaner and then wipe it all off. Use cotton towels.

After a sand blasting, what you are probably trying to do is get the metal polished smooth again. No more tools should be needed. The smoother you get the metal, the less work you will have to do when you prime the car. At this point, you have bare metal. All the OSPHO is going to do is protect it for 24 hours from developing flash rust. In your case, PyroSparks, I suggest you wipe the car down with OSPHO.