On another forum someone was asking about filler for powder coating. I found this and posted it there, thought someone on this forum might like to see the info also. Dan
Have been involved with powder coating for many years, and getting smooth pin hole free surfaces on casting etc is easy.
If you try to fill with a product you will probably only plug up the end of the pin hole leaving air trapped underneath,
When you apply the powder it will cover the surface but when the powder is then heated the air trapped inside expands and can push out the filler or the powder.
To fix the pin holes don't fill them, heat the article and then pull out of the over and then powder coat and put back into the oven and reheat the article. you can check out the pin holes are full as you apply the powder.
As the heated surface cools down as you apply the powder, the powder is sucked into the pin holes and then the surface flows out to make a smooth surface.
The better the surface the better the finish, just like paint, if there are marks the powder will follow the shape putting equal parts on the whole surface the marks will stay.
Only way out is to make the surface far better or sand the marks out in the powder when the job is cold and re do.