If you really want corrosion protection prior to painting steel, or galvanized metal, nothing beats Zinc Phosphate. It was developed by Parker chemical company, now Henkel. In crude terms it is phosphoric acid with zinc dissolved in it. From day one automobiles, tractors, or any painted products meant be outside for extended periods of time were coated with this prior to painting. When this chemical is applied to the surface of the metal substrate the acid etches the surface causing a rise in the pH at the interface. The zinc phosphate comes out of solution and forms crystals, which bond really well to the substrate and also give a very good surface for paint to stick to. The corrosion resistance of this treatment and paint is second to none. Even now no better products has come available.
For the home hobbyist or small paint shop here is simple method to apply it:
1. Purchase the solution
2. Clean the part with TSP (trisodium phosphate) and rinse well.
3. Acquire some spray equipment; I would suggest a Wagner electric spray gun. This has lots of plastic components so the acid will not harm it.
4. After a thorough cleaning, spray the part with the solution much as you would normally paint; doesn’t soak the crap out of it.
5. Wet a towel or blanket so it is just damp and cover the part. This is to keep the humidity up as it takes a while for the crystals to form.
6. The results will be a matt grey coating which is great for painting over. Once dry you can paint over it with primer and topcoat.
I think a story is the best way to explain the tricky part. Detergent has by nature a high enough pH to start the crystals to prematurely form so you need to rinse the part thoroughly.
Years ago a trade magazine on industrial painting had an article about Henkel and how they had put together a plan with Ford to do a reverse onus system on their pre-treatment systems (zinc phosphate). Ford would have Henkel take over their process and would then pay a unit price rather than directly pay for the chemicals. They had picked a truck assembly plant for the pilot and were getting all the arrangements. I had worked with Henkel products for years and wrote a letter letting them know that I’m your guy for the on-site position. First day on the job, I hung a bare steel test panel on the line, got it treated, e-coated, and top-coated. Gathered a few key people and then bent the panel, paint peeled back at the bend in a sheet. Gasps, first comment from one observer, quote “the paint and treatment or both peeling off”. My question to one of the Ford guys, what is your biggest quality problem. Their answer, chips and flakes on the final assembly line, which then had to be repaired. The following day I checked out the rinse section of the spray process and observed the many of the sprays were plugged. When the line was down for a break I got a closer look and saw wooden plugs where spray nozzles had broken. Keep in mind that unplanned down time cost the company a million dollar an hour. First order of business, have all the headers piping and nozzles replaced with quick snap plastic.
Lesson: make sure your part is well rinsed, no residual detergent. The last thing you want in the crystals prematurely precipitate out of solution.
Keep in mind the solution comes in different grades; you want the one designed for coating metal prior to painting.
For the home hobbyist or small paint shop here is simple method to apply it:
1. Purchase the solution
2. Clean the part with TSP (trisodium phosphate) and rinse well.
3. Acquire some spray equipment; I would suggest a Wagner electric spray gun. This has lots of plastic components so the acid will not harm it.
4. After a thorough cleaning, spray the part with the solution much as you would normally paint; doesn’t soak the crap out of it.
5. Wet a towel or blanket so it is just damp and cover the part. This is to keep the humidity up as it takes a while for the crystals to form.
6. The results will be a matt grey coating which is great for painting over. Once dry you can paint over it with primer and topcoat.
I think a story is the best way to explain the tricky part. Detergent has by nature a high enough pH to start the crystals to prematurely form so you need to rinse the part thoroughly.
Years ago a trade magazine on industrial painting had an article about Henkel and how they had put together a plan with Ford to do a reverse onus system on their pre-treatment systems (zinc phosphate). Ford would have Henkel take over their process and would then pay a unit price rather than directly pay for the chemicals. They had picked a truck assembly plant for the pilot and were getting all the arrangements. I had worked with Henkel products for years and wrote a letter letting them know that I’m your guy for the on-site position. First day on the job, I hung a bare steel test panel on the line, got it treated, e-coated, and top-coated. Gathered a few key people and then bent the panel, paint peeled back at the bend in a sheet. Gasps, first comment from one observer, quote “the paint and treatment or both peeling off”. My question to one of the Ford guys, what is your biggest quality problem. Their answer, chips and flakes on the final assembly line, which then had to be repaired. The following day I checked out the rinse section of the spray process and observed the many of the sprays were plugged. When the line was down for a break I got a closer look and saw wooden plugs where spray nozzles had broken. Keep in mind that unplanned down time cost the company a million dollar an hour. First order of business, have all the headers piping and nozzles replaced with quick snap plastic.
Lesson: make sure your part is well rinsed, no residual detergent. The last thing you want in the crystals prematurely precipitate out of solution.
Keep in mind the solution comes in different grades; you want the one designed for coating metal prior to painting.