<p>I'm trying to powder coat sheet aluminium which is not going as I was expecting, see photo:</p>
<p><a href="https://i.sstatic.net/XIzI4Gqc.jpg" rel="nofollow noreferrer" title="Photo of powder-coated sheet aluminium with bubbles and pits"><img src="https://i.sstatic.net/XIzI4Gqc.jpg" alt="Photo of powder-coated sheet aluminium with bubbles and pits" title="Photo of powder-coated sheet aluminium with bubbles and pits" /></a></p>
<p>The objects were prepared. Steps:</p>
<ol>
<li><p>Before:</p>
<p><a href="https://i.sstatic.net/OlhV7jo1.png" rel="nofollow noreferrer" title="Photo of pieces of sheet aluminium with paint on them"><img src="https://i.sstatic.net/OlhV7jo1.png" alt="Photo of pieces of sheet aluminium with paint on them" title="Photo of pieces of sheet aluminium with paint on them" /></a></p>
</li>
<li><p>Residual paint was sandblasted off:</p>
<p><a href="https://i.sstatic.net/Z451ez3m.png" rel="nofollow noreferrer" title="Photo of sheet aluminium sandblasted to show a clean surface"><img src="https://i.sstatic.net/Z451ez3m.png" alt="Photo of sheet aluminium sandblasted to show a clean surface" title="Photo of sheet aluminium sandblasted to show a clean surface" /></a></p>
</li>
<li><p>an epoxy primer was applied (<a href="https://en.coating4all.com/powder-coating-primer-pure-white-ral-9010?Product=398569086&amp;Lng=en" rel="nofollow noreferrer">Primer Pure white</a>);</p>
</li>
<li><p>the powder coating was done in a clean environment (<a href="https://en.coating4all.com/RAL-6034-Pastelturquoise-Satin-powder-coating-powder?Product=398572681&amp;Lng=en" rel="nofollow noreferrer">RAL 6034 Pastel Turquoise Satin powder coating powder</a>)</p>
</li>
</ol>
<p>The photo on top was taken after a second failed attempt on one of the smaller pieces. After the first attempt, the workpiece was lightly sanded smooth and all dust was removed.</p>
<p>It's not my first time powder coating, not even the first time powder coating aluminium. I'm surprised at how ugly the result is and I am hoping to find some explanations/tips here that I haven't considered.</p>

CC BY-SA 4.0
2024-05-14T11:44:05.530Z
The pattern of imperfections seems to correspond with that of the colors of the photo under step 2. The photo is very unclear, but I think the problem is present in the aluminium itself already. Are they perhaps bubbles, caused by corrosion or another process? (I'm not familiar with the technique.)
Joachim
CC BY-SA 4.0
2024-05-15T06:19:40.170Z
Some random ideas: was the air humidity higher than usual when you coated this piece? Or was it allowed to soak in water or some solvent and didn't have time to evaporate completely? Is there oil residue on the surface? This looks like off-gassing during the heating, so my approach would be to sand or blast the piece until you have an even, silvery color without dark patches and then wipe it with alcohol to remove any surface residues. Or heat-treat the piece for a prolonged time *before* applying the powder to evaporate whatever is causing this.
Elmy
<painting>
Powder coating problems on aluminium
ElRudi
# Powder coating problems on aluminium

(Asked by: username_0 on 2024-05-14)

I'm trying to powder coat sheet aluminium which is not going as I was expecting, see photo:

[![Photo of powder-coated sheet aluminium with bubbles and pits](https://i.sstatic.net/XIzI4Gqc.jpg "Photo of powder-coated sheet aluminium with bubbles and pits")](https://i.sstatic.net/XIzI4Gqc.jpg "Photo of powder-coated sheet aluminium with bubbles and pits")

The objects were prepared. Steps:

1. Before:

   [![Photo of pieces of sheet aluminium with paint on them](https://i.sstatic.net/OlhV7jo1.png "Photo of pieces of sheet aluminium with paint on them")](https://i.sstatic.net/OlhV7jo1.png "Photo of pieces of sheet aluminium with paint on them")
2. Residual paint was sandblasted off:

   [![Photo of sheet aluminium sandblasted to show a clean surface](https://i.sstatic.net/Z451ez3m.png "Photo of sheet aluminium sandblasted to show a clean surface")](https://i.sstatic.net/Z451ez3m.png "Photo of sheet aluminium sandblasted to show a clean surface")
3. an epoxy primer was applied ([Primer Pure white](https://en.coating4all.com/powder-coating-primer-pure-white-ral-9010?Product=398569086&Lng=en));
4. the powder coating was done in a clean environment ([RAL 6034 Pastel Turquoise Satin powder coating powder](https://en.coating4all.com/RAL-6034-Pastelturquoise-Satin-powder-coating-powder?Product=398572681&Lng=en))

The photo on top was taken after a second failed attempt on one of the smaller pieces. After the first attempt, the workpiece was lightly sanded smooth and all dust was removed.

It's not my first time powder coating, not even the first time powder coating aluminium. I'm surprised at how ugly the result is and I am hoping to find some explanations/tips here that I haven't considered.

**Tags:** painting

> **Comments:**
> **username_1**: The pattern of imperfections seems to correspond with that of the colors of the photo under step 2. The photo is very unclear, but I think the problem is present in the aluminium itself already. Are they perhaps bubbles, caused by corrosion or another process? (I'm not familiar with the technique.)  
> **username_2**: Some random ideas: was the air humidity higher than usual when you coated this piece? Or was it allowed to soak in water or some solvent and didn't have time to evaporate completely? Is there oil residue on the surface? This looks like off-gassing during the heating, so my approach would be to sand or blast the piece until you have an even, silvery color without dark patches and then wipe it with alcohol to remove any surface residues. Or heat-treat the piece for a prolonged time *before* applying the powder to evaporate whatever is causing this.  

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## 0 answers

