Ospho (phosphoric acid)

Jason86 · Post by **Jason86** » Tue Mar 22, 2016 9:30 pm

I just recently found out about Ospho (phosphoric acid) and using it on sandblasted/bare metal before priming giving it a clean and etched surface. It seems some people are for it and some are not. Is this something that you guys recommend and use on your restorations or do you just paint right away with red oxide primer? Im more of a mechanical guy so auto body is a new learning experience for me, I only plan on painting once and want to do my best to do it right the first time. Thanks for any and all advice.

jaycee · Post by **jaycee** » Wed Mar 23, 2016 4:22 am

i tried it years ago and i wasnt too impressed. after following the directions i had poor paint adhesion. i believe you are better off making sure the surface is dry and clean. while what im about to say isnt too practical for the body it is food for thought. take a bare piece of steel that you think is dry, play a propane torch over it and as you heat the surface watch the moisture come out of the pores of the steel. castings hold much more water and god knows what else. water on ferrous metals mixes with the carbon molecules making CARBONIC ACID this is what gets the rust process going. when i did my jeep in "rustville hawaii" every small part even the axles got the heat treatment. it was garage kept and had no visible rust through the five coats of primer and top coat after 20 years there. just my experience and my 2 cents worth.

oilleaker1 · Post by **oilleaker1** » Wed Mar 23, 2016 5:25 am

Phosphoric acid turns rust black and stops it. It also cleans off slight surface rust. Look up 3M Rustmort. It is absolutley NOT rcommended over a sandblasted surface. It bridges the pitting and won't allow paint to stick. Although it is good for rust, if you re-wet it, the rust takes off again. It works well on a soda blasted surface or chemically stripped surface. Only use sparingly with a rag and rubber gloves. Do not get it in your eyes or on you. Epoxy primer /sealer is your best encapsulating covering on bare metal. It's also very expensive. The world of auto restoration is being priced out of business by Uncle Sam. Anything the Gov't gets involved in raises the cost to you.

John

Bretto · Post by **Bretto** » Wed Mar 23, 2016 5:37 am

I'm sure you're just seeing condensation from the propane exhaust onto the metal surface. The by-product of burning propane is carbon dioxide and water. You'll get the same result if you do that on a cold piece of glass.

idiocrates · Post by **idiocrates** » Wed Mar 23, 2016 7:17 am

Phosphoric acid is a great etching compound to prepare metal for painting.....but......the surface to be prep'd MUST be oil and wax free or the phosphor won't be able to get to the metal. It seems a bit of a contradiction but after its applied it must be washed off with water. Failure to do so will result in very poor paint adhesion. And you must be ready to paint with primer immediately once the surface is dry....if no,t the metal will be covered with surface rust within a few hours. And its been my experience on using old oil field pipe for fence posts.....it does NOT remove or penetrate rust. It does NOT remove oily residue. Nor does it create any sort of lasting surface barrier. It DOES etch the metal it touches and in that regard it works very well. As with most chemicals, always read and follow label instructions and follow safe work practices. There should probably also be something mentioned about the run off of the water used to rinse the parts to prevent chemical pollution to our ground water and soil....but I'm not sure what. Good luck.

jaycee · Post by **jaycee** » Thu Mar 24, 2016 12:28 am

really? an oxyacetylene torch with a neatral flame with a neutral flame does the same thing.

Jason86 · Post by **Jason86** » Tue Mar 29, 2016 8:45 pm

Thanks for the replys. I'd rather not chance having adhesion problems with my paint after using phosphoric acid on sandblasted steel so I guess I'm going to just stay away all together. Besides making sure there is no lingering sand Is there anything I should do to my frame after I get it back from the blasters before I paint it, Am I going to be good to go with priming and painting right away? Is there anything I should be using to clean or prep the steel prior to painting? Thanks again.

Hawkshadow · Post by **Hawkshadow** » Wed Mar 30, 2016 5:41 am

Wipe it down with a wax and grease remover to ensure a residue free surface. I've had good results with Dupli Color's product.

http://duplicolor.com/product/grease-and-wax-removers

oilleaker1 · Post by **oilleaker1** » Wed Mar 30, 2016 5:58 am

Wiping down a sandblasted surface is a disaster with a rag. On a frame, blow it off and if you have grease areas, use brake clean and air. The rag will leave "hair" all over it. On body panels, Air sand it first to knock down the rough sand pitted surface with 80 grit. It will then wipe down much better with the recommended wax and grease remover. Blow off the "hair" the best you can and use a quality primer sealer. Then sandable primer top coat within the specified paint manufactorer's recommended time window for adhesion. If you wait, then the sealer will need sanding for adhesion. This all depends on what quality of job you are headed for. On Jeeps I drive in the woods and trails, I paint my frames with tractor enamel. It's soft and chip resistant. Cheap too. 30 bucks a gallon. Not UV resistant, but the mud doesn't care. If you are going for show, then as above and prepare yourself for a Gov't influenced sticker shock on price!!!!!!!!! like 650.00 a gallon! John

Hawkshadow · Post by **Hawkshadow** » Wed Mar 30, 2016 1:07 pm

oilleaker1 wrote:. On a frame, blow it off and if you have grease areas, use brake clean and air.

Good point! I've had good results using kimwipe over rags or regular paper towel.

Jason86 · Post by **Jason86** » Wed Mar 30, 2016 9:24 pm

Thank you for the replys I will go by that info for prep.

Ospho (phosphoric acid)

Ospho (phosphoric acid)

Prep and etch