Painting Stainless Steel

Ask an Expert From: Products Finishing, ,

Posted on: 8/1/2004

Question: I was interested in your solution for painting the stainless steel medicine cabinet, but I was hoping you would also include the “government job” solution done at work.

Question:

I was interested in your solution for painting the stainless steel medicine cabinet, but I was hoping you would also include the “government job” solution done at work. I, too, had to paint stainless steel. This is what I did and I am curious if you think it was right. I built a SS rudder for a 40-ft sailboat after the second fiberglass one broke apart. Then, after I had sanded and faired it out, I warmed it up and painted it with hydrofluoric acid to etch it, rinsed it and painted it with a wash primer. That was coated with a gel coat epoxy primer. Could I have eliminated the acid etch and just used the wash primer, or vice versa? B. C.

Answer:

Yes, your finish procedure was right but perhaps a bit risky. Stainless steel is relatively inert, hence paint adhesion could be a problem. Paint adhesion to stainless steel is enhanced by using pretreatments. Hydrofluoric acid etching is a pretreatment. Surface abrasion is a pretreatment. Wash primers are also pretreatments. I don’t like to recommend hydrofluoric acid etches because of the safety hazard. It must always be used under controlled conditions. Fortunately, you did not suffer any damage since you did it at work, hopefully under controlled conditions. When people use dangerous chemicals, I generally issue the following caveat: “Don’t do this at home kids!”

Now to answer your question, you can eliminate the hydrofluoric acid if you roughen the surface by abrading. This can be done by sanding, wire brushing or media blasting. It is important to note that the first step in any pretreatment is surface degreasing. After degreasing and abrading, apply the wash primer as soon as possible. After the wash primer has dried, the topcoat or gel coat can be applied. Since you are using stainless steel and corrosion is not a major issue, you can eliminate a corrosion resistant primer. Otherwise, a corrosion resistant primer such as a two-component epoxy should be applied over the wash primer and before the topcoat.

 


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