I have sanded off the surface rust on my 46 Ford hood and applied Ospho. It has left a rough coating on the surface of the metal. Do I re-sand this before primer to get it smooth again or build up surfacer/primer and keep blocking until it's smooth. I've never used this before so this is new to me.
Okay, please school me too... I had never seen 'Ospho' before tonight...grew up in the dry West Texas air. Naval Jelly was always my poison, for small spots.
from the directions, sounds like you prime right over it. thats how ive done it with other conversion coatings...1 coat epoxy then highbuild sandable primer
I use it all the time here on the coast. You need to sand it down to take off the roughness and you can respray or shoot filler primer or both. Just remember if you spray it when its rough it will still be rough but primered. Get it? Keep working with it cuz it all depends on the roughness of the surface you started with. I will sand and remove as much debris as possible then spray with ospho, light sand and filler prime. Good luck and keep us posted. People that don't live on the coast usually don't know this product even exist but it is a great product.
Ospho is simply phosphoric acid - same stuff in Naval Jelly - rust "converter" - some places carry the same stuff as concrete etcher. I do about what Aman said - get all the loose rust off, sand the surface down as well as I can, ospho it, brush loose off, sand down, prime.
I agree with Aman, Used it a little on my T body and I sanded it afterward, but we used it alot on headers and things like that ,and well we just primed over it. and like Aman said here on the coast pretty much every hotrodder or fabricator knows ospho
Ospho actually turns the iron oxide into iron phosphate (I think that's it) a form of metal. Cool stuff but do use with caution: Use eye protection, gloves and a mask, stand up wind if possible. Last time I didn't use any but, there was no wind and I burned me hands a little. Oh yeah, it turns everything white, especially the driveway for some reason. It's the only time my driveway is that clean.
after you sand it recoat it again with ospho, especially If you get the light dry rusty dust. Repeat the process as many times as you need to, esp if it is rough. STEEL WOOL will not clog as fast and will not scrape off the protective layer. After you primer it make sure you use a sealer or finish coat. Rust will sneak up if you don't. If going the CHEAP rattlecan route, use redoxide or zinc chromate primer, than an engine enamel than your flatcoat will last a long time. If doing it with a Newer style paint using a gun, you should be happy too. Good luck! TP
I use a product called Rust Cure that is another phosphoric based product. The instructions say to get a smoother finish, after you've applied some and its had some time to work wipe with a sponge while its still wet and apply more. Its worked for me, but I have not tried to paint over it yet.
Ospho, then sand it smooth, wipe on more Ospho. when you are ready to prime, wipe it down with metal prep or wash, shoot it, and continue as you normally would. I've used it this way before and after applying filler. I've only done filler directly to metal, with plain, old, non-epoxy, non-self-etching primer, but the way things are done now may be different, Ospho didn't seem to affect the filler. Great stuff, but is stinky.
I read the info on the ospho site. I have rust in the bottom of my doors like most old cars. Just a few pin holes through so far. Here's my question: Can I just pour this stuff into the door and slosh it around, drain out the excess and leave it to dry? Or do I need to paint inside the doors after to seal out any future rust? Thanks.
Just as Aman thought, the phosphoric acid in Ospho causes the surface of the steel to form iron phosphate crystals. These are a little rough and you can send them down. They are great for paint adhesion though. You can also put a light coat of oil directly on the phosphate to improve corrosion resistance if you do not paint over it. Ever see those fasteners used on a newer car that are a dull grey color? That is phosphate with oil as a protective coating.
I use it when I powdercoat old stuff, after media blasting, I wipe the pospho on and let it dry, sometimes I toss the part in the oven to expedite drying time, then I remove and green scrubby the crap out of whatever it may be. then dry wipe, no solvent and then I apply the powder. woooooooooooot rust be gone.
Great stuff. It will also pickle the surface and protect it from further rust formation. Will keep bare metal bare for a few months or longer. My body man buddy has a bug eye sprite stood up in his shop the was stripped to bare medal and OSPHO'ed. It has been there about 5 years now and no surface rust. I believe there is also a zinc component in the solution. I have been using muriatic acid after sanding, (use with caution and outside) it is a lot stronger than phosphoric and seems to do a better job of getting into pits. I then rinse with water and hit it with OSPHO. I believe OSPHO should be available in most any body shop supply jober. The OSPHO does a good job of making a primable surface.
Its also available at any home store...just look for green liquid rust killer...its sold under many names
So what is the white chalking? I thought it was a bad thing. I noticed it when the surface came in contact with water. I thought it was washing off the coating and thought the stuff was only effective if the surface was to remain dry until paint coule be applied.
Ospho is more than just phosphoric acid. O can leave patches of a hard thick black residue - PA doesn't. So the $64 question has always been, "can I paint over it" - especially when it forms these black deposits? Don't know what the black stuff is either. I think it may be brittle and will chip instead of being a tough polymer - but I'm speculating at this point since it's been many years since I used it. (I have used it since 1970).
Used it a bunch, but like others said, i'm close to the coast. I first heard about it from a shrimp boat captain, he said when they pulled the boat for hull painting that Ospho was all they used after blasting the rust-then just painted over it. He said it was the only thing could give any service life with metal hulls in salt water. I've used it on frames, etc. but never under a top coat. It just seemed too "iffy" to me for that-especially with the cost of top coat materials.
Some paint dosn't work over Ospho, great stuff that it is, SPI PAINT has a good article on there web site a good read
i actually started using phosphoric acid recently with good results, same process but I but it at Home Depot, used this on my mercury recently
You must Neutralize OSPHO WITH WATER!AMHIK! I OSPHOED A ROOF AND DIDNT NEUTRALIZE IT.THE SPI EPOXY PRIMER CAME OFF IN SHEETS!!!
Great! Can't you imagine spending multi K bucks on base/clears/reducers etc. , get a great job you're actually proud of--and then have it peel off in sheets. All for a $20. gallon of rust killer. Knife please.
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