We have a series of powder-coated electrical cupboards that need to be cut open to install recessed components. The exact product description can be found on the manufacturer's website.

The manufacturer describes the material as such (abbreviated for brevity) :

1.2 mm mild steel for enclosures ... Folded and seam welded ... Structured powder coating ... For outdoor installation, the use of a rain hood ARF and 100% polyester paint coating is recommended. The corrosion resistance must be taken into consideration.

The enclosures will be installed indoors but are expected to attain a service life of at least 20 years.

We want to install an embedded touch screen in the door and also install air vents and a cooling system on the side. This requires cutting openings in the door and sides.

How do I prevent the fresh steel around the cutouts from rusting?

From what I've found on the internet, it seems the best option is to re-powder-coat where we have cut (but I don't know how to do that), I was hoping for an easier solution :

  • A spray-paint type product?
  • A tar based plumbing product, maybe?
  • 3
    Seems pretty clear: "and 100% polyester paint coating is recommended. "
    – Ecnerwal
    Jan 28, 2021 at 17:04
  • Or, powder coating. There are places that do that and will do a one-off project. I'd suggest looking for "powder coating" in the yellow pages (that's the dead-tree version of your favorite internet search engine) and give a few a call. I don't think you'd need to do anything to the existing coating. They'll probably give it a good degreasing right before coating to ensure nothing is in the way of the new coat and that it sticks properly.
    – FreeMan
    Jan 28, 2021 at 18:16
  • 1
    Rustoleum 7769 Rusty Metal Primer. Dab it on with a brush. That's my go-to for stopping rust on outdoor things. Jan 29, 2021 at 4:17
  • Thanks @Harper-ReinstateMonica, that's whats I'm looking for!!
    – klonq
    Jan 29, 2021 at 12:26

3 Answers 3


Rustoleum 7769 Rusty Metal Primer is my go-to for outdoor things. The cleaner they are, the better it works, but it works with wire-wheel levels of rust removal.

I'm a "prosumer" painter. I know how to handle the dangerous stuff like LPU, and I don't mind paying $300/gallon if it means I'll never have to paint it again. I've delved deep into http://corrosion.ksc.nasa.gov and I'm willing to use the mil-spec 2-part chromate primers (the green stuff on new airplanes and locomotives). That's the only stuff I've found that will beat Rustoleum 7769 on clean metal (as in SSCP-SP10 near-white-metal prep). For worse prep (e.g. wire-wheeled) I simply haven't found anything at all.

The fact that Rusto 7769 is readily available in the consumer channel just makes it all the better.

Keep in mind my criterion is that it doesn't fail, until the topcoat above it fails. I prevent topcoat failure by using LPU topcoat, but you don't need to do that.

I would dab it onto the cut edge with the cheapest natural bristle brush at the hardware store, e.g. an "acid brush" (~3/8" wide) or a cheapie "chip brush". If you bought a spray can and realized what a mess that will be, and want to brush, simply shoot a little spray into a soup can (cleaned out and dried, obviously) until you have a tiny puddle of liquid paint.

Rusto is an "oil based" alkyd, and it will stink. There's no water-based product that will do what you want. (least not in the consumer tier).


Use the recommended paint. Clean the cuts and brush on a suitable base-primer coat first that is specific to steel and polyester paint.

Powdercoating processes seem to require

You would need to set up to do the baking part. Polyester paint can be sprayed or brushed. Does your application have trim bezels that will hide this type of touchup?

  • 1
    Yes, that's how powdercoating works. If you can hork together an oven somehow, the coating gun is $80 and powder is $5 at Harbor Freight. Jan 29, 2021 at 4:18

I've constructed and wired dozens of these control panels in the past and never used paint or powder coated any of the holes or cutouts I made. The meters, lights, push buttons, etc. I installed always came with heavy rubber bushings, gaskets, for both sides of the cabinet, sealing the raw metal. There were some instances where I coated the gaskets with a neutral curing silicone just to keep the customer happy. Many of these cabinets I've maintained over the years and have never seen any signs of rust. These were all indoor cabinets. You can use the polyester paint but I don't think it's necessary.

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