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topic 18298

Problems in powder coating

A discussion started in 2002 but continuing through 2018


Q. Following problems on mild steel panels powder coating are observed after the process is complete:

1) Powder peel off
2) Dust particles observed
3) Orange peel
4) Color shade difference one compared to other panels
5) Pin holes observed on the coated surface.

You are requested to give probable reasons and solutions.

Thanks and regards,

Jagdish S. Rane
- Pune, Maharashtra, India

User's Guide to Powder Coating
from Abe Books


High Performance Powder Coating
from Abe Books

Industrial Painting and Powdercoating: Principles and Practices
from Abe Books



A. Hi Jagdish,

The problems you are experiencing are quite common, I will answer then in the order you asked them:

1) Powder peel off. A. Poor adhesion caused by poor substrate preparation or insufficient curing. You must make sure the substrate is suitably pretreated.

2) Dust particles observed. A. Poor housekeeping, poor air control in your spray booth, etc.

3) Orange peel. A. A number of aspects may cause this, most commonly poor particle size distribution and poor gun control. (Try turning down kV on gun, and control your reclaim system)

4) Colour shade difference one compared to other panels. A. Poor oven conditions / controls. You may have "Hot Spots" in your oven. The work pieces must have the same curing conditions.

5) Pinholes observed on the coated surface. A. Cross contamination or back ionisation. Clean your system down thoroughly and make sure when you spray the gun is at least 12 inches (30 cm) away from the work piece. Try spraying at 70 kV.

Hope this helps,

Drew Devlin
- North Lincolnshire, U.K.


A. Dear Mr. Rane,

From your question it seems you are not using quality product. Please use quality product. Please tell me which colour you are using.

Kuldeep Verma


Hi Jagdish.

You seem to have mentioned just about every possible powder coating problem :-)

Can you tell us what kind of powder are you depositing and under what conditions. And also what is your pretreatment process? Thanks!

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 31, 2010

A. Hi...
To add reply from our friend - Mr.Drew Devlin -UK..
1.Powder peel off - mostly came from improper pretreatment process. Check with your chemical provider and please do daily check on your chemical level every time to start production , add chemical to stabilize the level if need
2. Dust particles - Make sure your powder booth is secure enough from dust. Some of applicator make room to secure the powder booth . Keep your house keeping well.
3. Orange peel - make sure your powder coating is orange peel . BUT if you use matte type and the result ...looks orange peel...make sure do not over thickness.. good thickness in range of 60 - 100 micron...if you use type matte and thickness too thick up 250 micron...there is orange peel effect come up..
4. Colour shade different - Check your oven ..stabilize your oven. Ask your powder supplier to check your oven and make sure your heat distribution is OK and match with your powder specification .. eg. 200 °C - 10 minutes. After you make sure it's OK .. then test your result using gloss tester ... and make it as standard (range).
5. Pin holes.... agree with Mr.Drew Devlin..


Kemal Miftah
- Jakarta Indonesia


Q. Dear Sir,

My question is about a rusting problem on powder coated panels. We have outsourced one of our products from our supplier which is metal enclosures for telecommunication kits. It is fully exposed to the outdoor atmosphere; it is rusted after a period of 11 months. The treatment is done for M.S., 7 tank process with hot phosphating. The powder used is pure polyester texture pattern.

telecommunication products - Bangalore, Karnataka, India

March 8, 2009

A. Hi,
As far as my knowledge is concerned I'm thinking that the powder you are using is not of good quality polymer percentage of the powder is to be checked so that it gets better response to your department. And secondly thing is to clean the proper specified area where process is done.

gaurav tanwar
- jaipur,rajasathan, India

A. Hi Srinivasan,

Depending on exactly what those enclosures look like, it doesn't surprise me that there is some rusting after nearly a year outside. I think electrocoat priming may be required in between the hot phosphating and the powder coating. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

August 9, 2012

Q. We are using polyester powder, we facing pinholes problem now ... so how to reduce?

ganesan [last name deleted for privacy by Editor]
- bangalore, India

August 9, 2012

Hi cousin ganesan. You've been offered similar advice by two experts, so the first question is whether you are following that advice? Did you start by cleaning your system thoroughly as suggested? If not, why? Have you already double checked that the gun is at least 30 cm away? If not, why? Are you operating at 70 kV, or are you unable to do it for some reason? Thanks!


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 10, 2012

Q. Hi. I use a number of different colour powder coats, but when I am using the colour "cloud grey" I have black speckles in paint (this is before placing in oven). I am wondering if it's the pigments in the paint? Regards, pete

peter thorne
- united kingdom

December 2, 2014

Q. You have not covered bubbles created during curing in the crevices of rims, which is the problem I have. Is the heat source too close to the rims causing this effect?

Edward Mitchell
- Langsville, Ohio, USA

December 2014

A. Hi Edward. "Rims"? Are you referring to automobile wheel rims? I don't know what you mean by crevices -- deep recesses in the design, or perhaps the bead area just inside the rim? Are these pressed steel or cast aluminum or what?

In any case, I think I would suspect poor cleaning before I would suspect overheating. We have a hundred threads about similar powder coating problems and probably half a dozen about cast aluminum rims if that is the situation. More data please, so we can direct you.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

April 22, 2015

A. Hello Dear,

We have that problem before but it's gone after using auto-machine and powder coating line system.
Try updates.

Jake Yeung
- Shanghai, China

July 23, 2015

Q. Dear Sir,


EP = epoxy-polyester

We are doing a coating on auto part size is about 1500 mm in length and 30 mm in dia. We used EP powder manufactured by a reputed company. But we face Pin Holes, rough surfaces, which are common problems -- but one more serious problem we face is that less coating is seen on the down side of the diameter; otherwise jobs DFT is about 80-125 micron.
Thanking You.


Rajendra gatkal
coatings - Chakan, Pune, India

A. Hi Rajendra.

The first step is to walk the line and see for yourself exactly what is being done. It is easy for me to picture an operator (or the programmer of a robot) spraying more lightly near the bottom, based on an assumption that the melting powder will run, and gravity will even things out :-)

Is there any evidence to suggest that the problem is more elusive than that? Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

Powder coating blotches

September 2, 2015

Q. Good day

My name is Etienne.

We have been experiencing blotches when powder coating various products, it seems that it is only when using a texture powder. And from various suppliers, we have had sales reps to come with new guns and we still have the problem.
We have found that it is more on prepared surfaces like grinding or brushed material from steel supplier.

18298-1aThumb  18298-1bThumb  18298-1cThumb  18298-1dThumb  18298-1eThumb  18298-1fThumb  18298-1gThumb  18298-1hThumb 

(click thumbnails to open hi-rez photos)

You can only see the blemishes when you look at the product from an angle.

adrian Botha
- roodepoort,gauteng, South Africa

September 3, 2015

A. Well,
There are several potential causes of this problem.
(1) Maybe you have a defective batch of powder. This unlikely but not unheard of.
(2) Maybe you are using a vibratory feed hopper rather than an aeration system? Special effects powders be they ripple or metallic or texture have to be aerated adequately.
(3) Maybe your air supply is inadequately filtered of liquid? do you have a well maintained and refigerant cooled air supply?
These are the three most obvious answers to your problems.
I hope this helps.
Bill Doherty

William Doherty
Trainer - Salamander Bay, Australia

September 8, 2015

Q. Hi William

Thanks for your response

(1) When the problem first occurred we got our suppler out (their technical department )and painted panels with them. They also had the test equipment to test the static of the units (all okay) they took a sample of powder back to the lab for practical testing (all okay). As you said, don't believe it is the powder (but was checked).

(2) Yes we do use vibratory feed hoppers they are ITC Gema (optiflex B). We have always used vibratory feed hoppers as we do 15 to 20 colour changes a day. We have had one metallic blue texture powder that we battled with to get the colour and silvery texture the same (this was not the blotches); this was due to the silver flakes and the base material separating (silver being heavier and settling to the bottom of the box). With our suppliers help we have overcome that problem by agitating the powder manually every now and then and by reducing the KV

(3) We have Kaeser compressors with the appropriate air dryers in place as we have highly moisture sensitive equipment in our factory that is all fed off the same air line (laser cutting machines).

We have also done the mirror test on our air lines at the points of painting and it was all dry and okay.

When we did tests with our supplier we took a mild steel plate and only polished a strip down the middle (so you had virgin material on each side and a polished piece in the middle). The blotches were only where the surface was polished/ground (we had the sandpaper supplier out as well, no problem there).

The blotches have also occurred on brush finished stainless steel (rough surface); we have never had blotches happen on untouched surfaces (cut and bent parts). The blotches only happen every now and then and only on surfaces that are rough; this is very confusing for us as we and our supplier have not come across this in the past.

Hope the new information helps and your input is highly appreciated.


Adrian Botha [returning]
- roodepoort,gauteng, South Africa

September 9, 2015

A. Hi,
I find the last two paragraphs of your response puzzling.

Am I right in concluding that only the polished (or sanded) section on one occasion has the flaw but on another occasion the flaw is on unpolished (not sanded) surface?

I really think you should try a full on aeration hopper scenario for the special effect powder you are using.

Metallics can be bonded or not in formulation. Textures, ripples etc, I do not believe can be.
Give an aeration hopper a try if only for special effects and please advise your result.
Hope this helps.

William Doherty
Trainer - Newcastle, NSW Australia

September 9, 2015

thumbs up signHi.

Yes you are correct in saying that it only happens on sanded or brushed parts of product and never on parts that have not been sanded or brushed (plain mild steel)
I will have to get hold of our gun suppler and get a demo gun to try (worth a try ).

Thanks again for the feedback, it really is appreciated


Adrian Botha
SPE - South Africa

September 12, 2015

A. I like Bill's suggestion of aeration stirring rather than vibratory.
We've found that vibration causes many problems in special effects, metallics, and textures. Air fluidizing solves most of them.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland

September 14, 2015

A. You only need a fluidising hopper.
Your gun and the rest of your gear could remain.
A fluidising hopper is a cheap and easy construct.
I am really interested in your result, please publish.

William Doherty
Trainer - Newcastle, NSW Australia

September 23, 2015

thumbs up signHi all

Thanks a lot for all your input.

Since my last post I have had a demo from Gema of their fluidise unit with the hopper.
Been running it for a weak in my batch line.
I have compared the work from the batch (hopper unit) to the work from our other two conveyer line (vibrating units).
I cannot see a difference in the finish of the end product in structure, hammertone, texture, and metallic colours (special effects powders).
I still can't see what will cause the blotchiness. Thank goodness it has only happened twice this year.



Adrian Botha [returning]
SPE - South Africa


Clearcoat pulls away from edges, and pools at bottom of parts

December 19, 2015

My issue is my transparents seem to pull away from the edges of my parts and pool at the bottom of the part. This is new metal and it's clean, so no grease or polish on it, etc. I'm so frustrated I just can't figure out why they are doing this; my edges are not sharp and my oven is at the temperature the manufacturer specifies. If you guys have any ideas as to why this is happening I'd be very grateful

Steve Clark
- Westbank, British Columbia, Canada

December 22, 2015

A. Good day Steve.

Interesting situation. I am by no means a pro at paint, but I am involved in paint adhesion testing wet/dry with primers and epoxy top coat for aerospace. You mention this is new metal. What is it and what are the previous metal compositions?
"This is new metal and it's clean, so no grease or polish on it, etc." Can you verify?
Do you have a process to clean prior to paint, and does the part exhibit a water break free surface before paint?. It looks like the paint is not "biting/adhering" at the edges which are not sharp, and at the perimeters of the holes, and as you say it is pooling at the bottom. Are you dipping or spraying? Obviously you are confident with the viscosity. Have you done a paint adhesion test on these parts?
Food for thought.


Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada

December 22, 2015

Q. Hey Eric
By new metal I mean that it hasn't been used for its intended purpose yet. So in this case no bearing grease, etc. As for the type of metal it's aluminum; it was cleaned just with water then out gassed in case there was any cutting solution on it from the CNC machine that made it. I lightly rubbed it with triple 0 steel wool and washed again. I have powder coated many things and only in the past few months have I tried the transparent top coats. This one being a copper, there is no base coat under this and the manufacturer said I didn't need one.

I did try putting a metallic base powder under it and had the same issue, again doing so under the manufacturer specifications.

Just so stinking frustrating since removing powder coat from corners can be a nightmare. So any help is good help at this point. And thanks for taking an interest in my problem, Eric.

Steve Clark [returning]
- Westbank, British Columbia, Canada

December 23, 2015

A. Good day Steve.

I do not understand that it was just cleaned with water and out gassed. I am having a problem with the STEEL WOOL on aluminium and washing again.
Washing with what?
Since this is a "new" metal, (is this the first time processing aluminum?) perhaps this is a situation where the cleaning chemistry (powder coat) is not compatible with the aluminum. Your alternate metallic base also proved negative.
When I have issues with paint (we process aluminum as spray), I process the items with a pre-anodize cleaning process.
It involves a wash/wipe with MEK (that is ONLY what is allowed following specs), MILD alkaline soak (high caustic/high pH will cause you grief), to remove any trace of "exotics", and a deoxider to deal with any oxides, if there are any, based on the alloy.
Maybe I missed the train.


Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada

December 23, 2015

A. Your coating is too low in viscosity, or is applied too thick.

Try two layers, each half as thick. Let the first layer air dry before applying the second.

If you do not see the problem prior to bake, the coating may be thinning as it begins to heat in the bake oven. You can try air drying to let it thicken up a bit before baking.

Your part looks like the armature for an ignition coil. Most mfrs of those use precoated sheet and don't bother to coat the edges at all.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

March 28, 2018

Q. Hi, my question is in powder coating. Aesthetics is the major problem or what? How to reduce that problem?

Nelson j. simon
ups pvt ltd - bangalore, india

March 2018

A. Hi Nelson. I think we're going to need more words than that before we can help you much :-(


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

Rough edges on metallics

May 23, 2018

Q. We are having issues with rough edges and some bubbling when spraying metallic powder onto aluminum castings. Part process is: 3 stage washer - dryoff oven - robotic powder epoxy prime - oven cure (parbake) - robotic topcoat powder (bonded uerethane metallic) - oven cure.

While the majority of the part comes out great, a thin fin coming off the part will either have a rough abrasive edge, or a slightly bubbled edge. We have experimented with several powder flows, and electrostatic settings. We are able to eliminate the bubbles by lowering the Topcoat film build. But then the rough edges turn up. Occasionally, we will turn out a rack or so of good parts, then slowly back to rough edges. Lowering the electrostatic KV and Ua levels seems to make things worse, while high KV seems to help. At a loss.
Any input would be appreciated!

Christopher Shepro
Robotic Powder Paint Tech - Fond du Lac, Wisconsin USA
  ^- Privately contact this inquirer -^

May 25, 2018

A. Hi Chris, you are obviously looking to a high quality protective finish and, by the sounds of it, working well towards that.
That said, it would be very helpful to view photographs of the problems.
A picture is worth a thousand words?
I trust that your powder delivery system for metallic is aerated rather than vibratory?
Please provide photographs to allow any constructive further advice.

wiiiam doherty
trainer - newcastle nsw australia

Black "rub marks" on powder coating

August 14, 2018

Q. Hi guys, we have a problem that, after the supplier sent in the parts, when we are about to use it we found that there is serious rubbing marks (black) on the powder. I would like to know what is the root cause of this rubbing mark? FYI, we are facing this issue when we rub the parts with a clean soft cloth. Is this because of the quality of the powder or what?

Moon Radzuki
Actiforce Mechatronics Sdn. Bhd. - SUNGAI PETANI, KEDAH Malaysia

August 22, 2018

Please add the photos that will maybe explain the problem.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland

Ed. note: Photos can be e-mailed to

'Spiderwebs' in powder coating

November 21, 2018

Your Q, A, or Comment: hi. I have a problem like spiderweb on my finish ... why? It's happening only with white.

Lorenzo bonini
- Firenze, italia

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