A question for the Powder Coaters...

[Scratch]

I'm finishing up a railing job and will have it PC'd. This is the first time I've had anything PC'd. I've ground down all the surface welds with 80 grit flap discs and they are pretty smooth. Should I go with a finer grit that that? Maybe a DA sander? I know from painting cars how deep a scracth a certain primer/surfacer will fill, but I don't know about PC's. This will be standard satin black.

The guys at the PC place also said it's not necessary to sandblast it if it's clean new steel, even with that dirty black coating that rectangle tubing has on it. They have some wash/degrease/wash/dry/ method that will be fine as long as it's not rusty. That true?

[JJ13]

Sounds ok. I would still prefer my stuff be sandblasted to allow for better adhesion. As far as the surface finish goes, I would treat it similar to something you were going to spray primer on. The powder will fill some pretty heavy sanding scratches.

[bigtoy302]

For best adhesion, all parts should be sand blasted and Iron phosphated. You can coat clean new metal but it will not stick the best and won't last very long. On a interior part this is ok, but for a part like hand railing it really needs to be blasted and phosphated. If a shop says they can coat over mill scale you need to find another shop fast.

Ryan

RyDel fabrication LLC

[Loyd]

We used to powder coat 1,000,000 lbs of HRS (hot rolled steel) with mill scale every year. It was not sandblasted, it did go through a 5 stage iron phosphate wash. It was for outdoor use exclusively. If the parts were to be used in Hawaii or Alaska then it went for .003 to.005 zinc phosphate coating before powder coating. In the mid '90's we were producing 85,000 units per year in this manner. We were using minimum 120,000 pounds of powder per year. Outstanding salt spray, rub and scratch tests. I used to build burglar guards and ornamental iron fencing/gates. If I were to do a job as you are doing I would sandblast, phosphate and then powder coat.
Loyd

[AnotherDano]

Find a new PC place.

That mill scale should come off before the other steps and blasting is the best way to get it done.

As far as covering the sanding/grinding marks, you'll find that the powder coating will do a much better job than paint. If it's one of those jobs that requires NO scratches, hit it first with a primer (powder coat, like KL) and lightly sand it if necessary.

[jeeplogic83]

I agree, sand blast first, and if it is going outside make sure they use a primer coat you will have much better results in the long run.

[CPK_Jim]

Yes sandblast is the way to go. Powder coat itself is very tuff stuff, the problem usually lies in the adhesion of the coating to the substrate. Blasting gives the powder something to hold onto. It is more difficult to remove coating from a blasted surface then from one that has not been blasted!!!!


Jim

[AnotherDano]

Hey Scratch,

How about an update?

[Scratch]

I ended up going with another place. They have some big automated line, that dips the stuff in a degreaser, then a washer, then a phosphate bath, another wash then PC.

Turned out great, the client surprisingly showed up early as I was pulling into the driveway with it, loved it and took it right then. I'll try to get a pic of it after he installs it.

I really like that PC stuff. Looks real nice. Thanks for all your help.