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Powder coating on epoxy paint results in pin holes

2007

Sir,
We are doing black powder coating on Malleable iron door fitting, we are unable to control the pin holes.
Please suggest, we are doing phosphating and a coat of epoxy paint before Powder coating.

Vikram Batra
Partner - India

Are you using a solvent based epoxy paint before galvanizing? This is liable to evolve volatiles in the curing of the powder, which must go somewhere - and thats out through the newly forming powdercoated layer - causing pinholes.
Why do you paint before powdercoating?

If you want epoxy for chemical resistance, why not use epoxy powder?
If UV resistance is a problem then perhaps epoxy powder overcoated with polyester powder.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

2007

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2007

Sir,
We apply epoxy coat to make foundation (or you can say base of the product), because our malleable iron products look like olden days products as the surface is not smooth.
You must have seen in U.K. and Ireland.

Vikram Batra
- Aligarh, India

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I suggest you try some with epoxy powder (or even polyester - you didn't say why use especially epoxy).

If you really need coating thickness, then either coat thicker or 2 coats.

If you need an ancient look then use a textured powder, or even one of the antique powders (a special look to make things look old).

I suspect your pinholes come from the paint under powder.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

2007

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Pinholes on epoxy can be attributed to a few different areas such as my colleagues have discussed. One thing that epoxy powder needs to happen is to enter the oven at a sustained high temperature in order to make sure the epoxy topcoat flows immediately. If this doesn't occur, one result will be pinholes due to the surface inconsistencies and volatiles escaping. When the powder is subject to high heat as that of an Infra-red system, it will flow much quicker and help eliminate those pesky pinholes.

Bob Utech Benson, Minnesota

Ed. note: Bob is the author of: "High Performance powder Coating" on eBay or AbeBooks or Amazon [affil links]

2007

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I suspect that the epoxy process is contaminating the topcoat. Are the two steps in close proximity to where overspray from the epoxy might get on the powder topcoat before it reaches the cure oven? Also look for other sources that can cause pinholes like people using spray paint in or around the area where the freshly powdered parts are traveling. Something atomized is definitely floating around your shop and causing the pinholes.(Pinholes are caused by airborne contamination)

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2007

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Dear Vicram,
I think everyone is confused by your original posting, i.e. the use of the word "paint" as opposed to powder. We need to establish a few basic facts:-
1) Are you using paint or powder as the first coat?
2) Why are using it? Is it used as a primer because the metal substrate is pitted or for some other reason?
3) What colour and effect do you wish to acquire from the final coat?
We supply a UK door furniture mf whose product tries to simulate those of an antique nature. The metal castings incorporate a hammered effect and they only apply one coat of 20% gloss black polyester. Are your items pressing or castings?

Terry Hickling
Birmingham, United Kingdom
2007