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topic 60290

Can I plate over zinc phosphate?

October 12, 2016

Q. I have been re-plating some motorcycle parts with zinc at home. I have experimented with electrolytic rust removal but have had better results mechanically removing it (wire wheel in angle grinder) or chemically removing it.

I have some POR-15 Metal Prep [linked by editor to product info at Amazon] and the label says it leaves a zinc phosphate layer. Can I can electroplate zinc over that?

Also, Evap-o-Rust [linked by editor to product info at Amazon] seems to work very well; Can I plate after using that or would I need to strip whatever its rust barrier is first?

Bob Kingsmill
hobbyist - Kawartha Lakes Ontario Canada


October 2016

A. Hi Bob. Sorry, but you can only electroplate onto raw, clean, active metal.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


October 14, 2016

Q. Thanks for replying so quickly and thanks for spending the time to answer questions from so many people like me. I have read so many of your answers on finishing.com that I have found on google that I almost feel like I know you.

I didn't think zinc plating would stick to the phosphate but I wanted to ask someone much more knowledgeable. I won't try that.

At the same time as I posted my question I also asked at Evapo-Rust's site. The reply from David Harris was "You can plate steel with no problem providing the steel is well rinsed with water after using Evapo-Rust."

I figured it was worth a try so I left the worst piece I am currently re-doing soaking in Evapo yesterday while I was away at a funeral. Today I rinsed it well, went over it with a wire brush and rinsed it again. One end of it is in my little plating tank as I type this and it seems to be plating well. We'll see what happens when it gets to the brush & buff stage.

I have another question if you don't mind. I have been using the typical hobbyist's setup: A bucket of epsom salts & vinegar electrolyte with strips of roofer's zinc hanging over the edges powered by a battery charger with assorted auto bulbs to regulate the current (I have a rheostat that I intend to install in the charger when I get a chance). I have read about other metals like tin being alloyed with zinc to produce more durable plating. If I was to add a piece of the other metal into the bath, connected to the same polarity as the zinc would it produce a similar result? If so, which metals would be best?

Bob Kingsmill
- Kawartha Lakes Ontario Canada


October 2016

A. Hi. Happy to 'know' you, Bob.

If you are wire brushing all of whatever you put on the steel back off, it doesn't interfere with the plating. If you are leaving some coating on, it's a problem. The question is not whether current will flow to the part and zinc therefore deposit; the question is whether the resultant plating will be useful or not. One measure of usefulness in many if not most applications is adhesion, i.e., will the zinc stick or will it pop off as soon as the going gets rough. Bake the parts, or hit them with a chisel, or bend them around a small diameter mandrel and educate us on what you find. If you're back to raw steel, and have done the plating right, it will stick; if there is anything left between the raw steel and the plating, it can't stick properly.

In general, alloy plating is very difficult. If you recognize that a battery is just two different metals placed close to each other with a conductive medium between them, you can see the problem in trying to get ions of both metals to deposit: one will have great power towards constantly pushing the other back into solution. Generally you need to use cyanide (a definite no go for hobby platers) or some other complexing agent to "tie up" the more noble metal (tin) or zero zinc will deposit. You may be able to buy a tin-zinc plating process which includes the appropriate complexing agents but you probably won't be able to make one from raw chemicals. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


October 14, 2016

thumbs up signThanks Ted. I didn't think it would be as easy as that but I would have felt pretty dumb if I found out later that it was (as I did when I found out how easy basic zinc plating is). And you're right - I don't want to start working with stuff like cyanide at home.

Re: Evapo-Rust, I just used a hand held brush (not the wire brush in the angle grinder), more to scrub it a bit than anything else. When I take parts out of the tank I normally rinse them and then go over them with a brass brush, then buff them (I believe that a smoother surface will shed water &c and thus won't rust again as fast). This time after the brass brush I heated it up to hotter than I wanted to hold onto and then went over it with the steel hand brush and all it did was get shinier (I don't think I will buff this one). After that I struck a chisel on it and it dented the plating & steel but nothing flaked off or any thing so I think it is OK to do it that way.

I have a feeling that if I didn't rinse it right away there would be a coating I couldn't plate through, though.

Now if only I could find a cheap & easy way to permanently fix rusty chrome we could all get rich from it ;)

Bob Kingsmill [returning]
- Kawartha Lakes Ontario Canada



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