I have an F-1 bed that I had sandblasted a number of years ago, it has a good coating of surface rust that we have treated with phosphoric acid and then wire brushed. Is there anything else we need to do to it before priming?
Hey, I'd suggest you continue to use the phosphoric acid/metal conditioner untill all of that surface rust is gone. Wash the surface with lacquer thinner, DA with 80 grit, and prime with a good urethane primer. Today's epoxy primers don't have the rust preventive elements of yesterday. " Life ain't no Disney movie "
I use a product called GemRust. I apply it with a spray bottle. It will dissolve the surface rust however once it is dry you will need to remove it before applying any coating. I use a stripping pad from HF on an angle grinder or a DA with 80 grit to get a clean surface. Eastwood's sells the same stripping pads but the price is double. If your piece has joints and crevases which the acid get in you will need to neutralize it before coating. In such cases I use a product called Prep Step marketed by Zero Rust but it is better to get in and manually remove any acid residue with a wire brush and the Prep Step solution. There are many different products marketed for the same purpose. The ones I use are effective and cheaper in my opinion.
Thanks for the replies. The bed is going on my sons F1, I hope to prime it this weekend and wanted to make sure We did it right.
If you don't remove the acid while its still wet and active your leaving yourself open to epoxy failure. If it dries on the metal its best to reapply and let it reactivate the residue then wash with lots of water blow dry with shop vac then prep and prime.
The instructions for some phosphoric acid cleaners say you can let it dry and paint over it. I don't like that idea. I always rinse then immediately dry.
Ive used about four different brands of phosphoric acid treatments and allowed them to dry and then primmered over them, usually with PPG DP epoxy, with no problems. However, there have been problems reported with other epoxy primers, I assume because they are etching primers with there own acids in them that are not compatible. I like the phosphoric treatments to treat bare metal and protect them till I can get around to primmering them.
Can you expand on this statement. Is this a treatment process applied after removing the rust? If so, can you give me a product line to look at. I am trying to buy some time between the rust removal bare metal stage and primer.
I usually use OSPHO or Jasco Prep and Prime which I found at Lowes before. Neither one of them are very good at removing anything more than light rust; that takes multiple applications with scotch brite or steel wool pads. They impart a phosphate conversion coating on the treated metal as it dries that retards the rust.
I use Blue Lightning Metal Prep, after the rust remover. The Metal Prep also leaves a phosphate coating, once dried.
Blast it again, put some rubbing alcohol on it to get all moisture out of the pores, and epoxy prime it right away.
From the Spec sheet for PPG DPLF under preparation · Chemical treatment or the use of a conversion coating will enhance the adhesion and performance properties of the finished system
Read the tech sheet on whatever material you are planning on spraying. I've been using House of Kolor DTM Epoxy primer and the tech sheet specifically states that you will have adhesion problems if you don't remove all of the phos acid from the metal. Other primers might be different, I don't know.
This is for the HOK KP2CF primer. I am curious if a dried coating of phosphoric acid would need to be reactivated by first applying more product or would following the directions below suffice? NOTE: IF YOU FIND IT NECESSARY TO USE A METAL CONDITIONER TO REMOVE RUST, ETC., BE SURE TO THOROUGHLY CLEAN AND NUTRALIZE THE TREATED AREA FOLLOWING THE CONDITIONER MANUFACTURERS RECOMMENDATIONS, USING OUR KC20 POST SANDING CLEANER WITH A MAROON SCUFF PAD TO INSURE ALL ACID RESIDUE HAS BEEN REMOVED BEFORE PRIMING. IF NOT, THIS WILL ALMOST CERTAINLY CAUSE AN ADHESION PROBLEM
As I understand the 'rusting' process, rust in it's first stages is a protective, 'oxidation' coating that forms on bare metal as somewhat of a protective coating... As the rust coating matures, it tunes into a destructive action because it holds water and other contaminates that eat the metal up. There are several 'rust transformers' on the market, OSPHO is one of them,, Jasco also makes an excellent one as does Eastwood.. The rust transformers work very well to stop light rust on bare metal.. They will stop rust from forming for several years when a body is in the process of being restored.. The rust transformers usually take at least 12 hours to work. Following application they will turn light gray to black which is an indication that the phosphoric acid has done it's job. I have used OSPHO and the product made by EASTWOOD for years, they work great if you follow the directions on the containers.
Bill is correct, most industrial companies use a phosphoric wash to eliminate embedded corrosion and/or rust. In the Steel Structures Painting Manual it state that paint will adhere the best to a slightly acidic substrate. Epoxies hold the best. In the car world a finish paint system needs more attention but you still have to eliminate the micro corrosion and phosphoric acid at a high dilution rate works great to eliminate flash rust or to prep before painting and it does not have to be wash off. Just let it dry and paint. Auto manufacturing plants use a wash or acid prep system before painting. In the ship building industry a phosphoric flash rust eliminator that is painted over will increase paint adhesion and is used everyday.
As I stated earlier in this thread, I would highly recommend that you read the tech sheet for your particular product...or, you could just follow this advice and take your chances. Personally, I will follow the paint manufacturers recommendations.
The Jalopy Journal
