clear powder over patina...

[Cracker Red]

I want to start powdercoating clear over my steel pieces. Every time I send one to the powdercoater it drastically changes color from deep bronze to a greenish yellow.

I spoke with Bill yesterday who told me it was cooking for too long. Followed prismatic powders directions to a "T" for clear today (400deg PMT for 10 mins) and it was again yellow green coming out of the oven.


I'm worried to use spray clear on outdoor steel pieces....Ive not had luck getting the rust protection that powdercoating offers....always seems to spider rust from the edges in 4-5 months. I can't sell items to customers I know will rust on them....can someone point me to what I'm doing wrong?

[comeoutswingin]

Its cooking too hot. I discovered this issue when I was still doing the patina stuff.. I cured at 250 degrees.. which is under curing, but for these, durability doesn't need to be the same as say a bumper..

[Cracker Red]

I'll give it a try. I have a duel use booth (powder and clear/dye) but never have luck with clear coating steel pieces....all end up rusting along the edges no matter what I do. Being that I'm in FL I battle the climate 10 months a year.


How long did you cook it for?

[blackandtan]

I guess I'm not the only one in Florida fighting this issue with rust. I was wandering if using clear powder would help with that.

I'll give it a try. I have a duel use booth (powder and clear/dye) but never have luck with clear coating steel pieces....all end up rusting along the edges no matter what I do. Being that I'm in FL I battle the climate 10 months a year.


How long did you cook it for?

[comeoutswingin]

The edges are probably rusting from edge pull.. basically the powder doesn't adhere to the tiny sharp edges of the steel, as it cures it pulls away even more. I get it a lot on black powder.. best solution? sand the edges until they're smooth and dull. (lots of work and on artwork, pretty much impossible.)

[Cracker Red]

It's not rusting with powder on the edges....only with clear coating. No problem with clear power, aside from the color change with patina...

[GDS Metal Worx]

Columbia coatings has a low temp cure clear. Try that out. I use super durable wet clear from columbia and have had no issues. I also cure at a lower temp, around 350, and bake it just a little longer.

[motoguy]

I finally got my powder setup going, and powdered my first parts today. I ran into the same issue with a patina test piece. Went in looking normal, came out blown all to hell! Ugly gold/yellow/green looking thing.

I did some digging on Bill's site, and found a FAQ where he basically suggest minimizing heat exposure. Don't heat-soak the part. Don't run full cure time. Don't let the part cure in the oven. He suggests pulling the part as soon as the powder flows.

I made a 2nd piece, and tried his suggestions. I pre-heated the oven to 400 degrees. Coated the part, stuck it in the oven. I checked at 3 minutes, and it had flowed out nicely. Pulled the part, let it cool, and have the BEST looking clear coat on a patina part that I've ever had. I don't -think- there was any change in the patina, however I'm going to run a couple more at 2 minutes and 2:30 to see if there's a sweet spot.

BTW...my Sharpe Finex 1000 gun arrived just the other day. After today, I don't know why I would ever want to spray paint again!

[anvilhead]

You will want to do a MEK test on your finish. We powder coat and I feel like your finish is not fully cured. Put some MEK on a rag and wipe a hidden area and see if the finish can be pulled off with the MEK. If the powder is fully cured the MEK should only dull the finish. If these parts are going outside and the clear is not fully cured you will have powder failure - when - not sure - only know that failure will happen.

CG

[anvilhead]

We use Sculpt Nouveau for clear coats over patinas. We powder coat and prefer the Sculpt Nouveau for clear over patinas. They have several clear coats available with UV protection. For durable applications they have a two part clear system. Worth checking in to. Good people to deal with.

CG

[motoguy]

I have since found that 370 for 9 minutes works great. Part looks good, retains color, nice finish, etc. That's 9 minutes from door closing to door opening and pulling it.

Yes, it's under cured. How much? I don't know. I have had no complaints. I can tell you that 10-11 minutes leads to a greenish/yellow, roached part. Perhaps I can lower the temps further, and cure longer. I believe 30 mins at 325 will still achieve full cure for Clear Vision. I will play with it once I'm in my new building.

[jproberts]

Now there are new powders with low heat curing (like 180 degrees) and short bake times. IGP developed these for powder coating on wood, could possibly work on patinated metal and be a good solution to this problem.