Overpainting Powder Coated Steel

I have just acquired a loco with some powder coated parts and these, particularly the bogies, have scratches in.

Obviously they could do with touching up but I am concerned that the powder coating will still scratch and the overpaint will fall off unless removed which I suspect will be the impossible side of difficult.

Any suggestions?

Hi Nick

If the scratches are down to the metal then make sure no water can get in otherwise metal corrosion will lift the powder coating, perhaps there is a paint that can fill the scrathches and be buffed down to blend in.

Emgee

Powder coating creates a smooth, flat finish and paint will struggle to bind properly.
Chemical strippers will soften and remove powder coating if you want to completely re-paint the part.

Otherwise to prepare for painting
You must clean off all dirt and grease.
Sand with fine paper.
Wipe down the area you will be painting with an appropriate solvent cleaner.
Rinse with warm water and allow it to dry.
Apply a suitable primer. (Not an etch primer which is used on bare metal).
Test for adhesion by applying a small spot of primer first.
Wait 20 to 30 minutes and then try and wipe it off.
If it wipes off easily, smears or smudges, it means there is not enough adhesion between the paint and the surface.
Once the primer is dry, you can apply the paint.

If it is just minor scratches, use the old motorcycle show trick and fill them in with felt pen of the matching colour. The permanent marker ink is surprisingly long-lasting.

I have overpainted powdercoated parts often - mostly to have multi-tone colours on a large powdercoated part - never sanded or roughened the surface prior to painting. Also never used a primer.. All I have done is wet the area profusely with lacquer thinners till the surface is notably tacky, and then paint on the new paint right away - I have used enamel ( turpentine base) and Lacquer or Thinners based brush-on, roll-on and even rattle can spray paints. I have examples that I did 8 or 9 years ago and there is no loss of adhesion at all..Quick, easy and no fuss.

Edited By Joseph Noci 1 on 13/03/2023 07:48:13

Powder coating can use various different polymers, so the behaviour may vary. That's not to criticise any of the responses above - just be aware that you could have a different coating type.

Epoxies and Polyesters seem to be common, but there are other materials types.

The powders are chosen to have good adhesion to the substrate, so hopefully will also allow the paint to bind chemically...

When I had new windows fitted to the house a few years ago, they were powder coated aluminium frames.

I was supplied with some touch up paint should it be needed. The paint appears to be a two part epoxy - the instructions say mix 4:1 paint to what I take to be a hardener. There is no information beyond the colour, the mix instructions, the usual safety warnings and some part numbers which appear to be based on the window suppliers order number.

A call to your local powder coating firm might elicit some information on touch up paint.

PS an online search for "powder coating touch up" gets lots of hits

Edited By Peter Cook 6 on 13/03/2023 14:05:50

2 years ago I repainted my garden tractor which was exhibiting the usual problem of rust running under the original powder coated finish. I derusted and used a medium grade production paper to give the undamaged powder coat a key. Two coats of decent undercoat and enamel top coat (Craftmaster). After two years outside under cover, there is no peeling or lifting, the surface is still shiny, and the interface between the powder coat and bare metal is virtually invisible. On that basis I wouldn't worry about overpainting.

Exactly my experience.