Micro Porosity In Paint (1 Viewer)

[RUSH55]

Sprayed some single stage acrylic urethane at its recommended viscosity (no more than 10% reduction) on the roof of my 55 which resulted in gnarly orange peel. After waiting for the appropriate time I started color sanding in an effort to knock everything down flat. What I began finding was this micro porosity in the paint. Haven’t talked to the “rep” yet as I’m trying to get things corrected on my own first. Can anyone tell me what the possible causes could be for this condition and what some possible fixes could be, shy of a complete re-strip and re coat?

First pic shows the orange peel

Second pic shows how much it needed to be knocked down

Third pic shows the porosity (might need to zoom in to see it)

 

[RUSH55]

Possibly found some answers to my own questions that I’ll go ahead and share…

Talked to a body and paint guy I work with today. After asking a few questions, he asked what I cleaned the surface with, which I replied “acetone”, and not wax and grease remover. He said acetone can leave residue which could possibly cause this porosity as the paint not evenly adhering to the substrate. Which sums it up as possibly a reaction.
Did more searching on YouTube and found this video on “Solvent Pop and Fish-Eyes” which goes into more depth on causes that would create this problem. Those causes include -
Too heavy of a coat
Wrong reducer
Too high air PSI



Looks like I get to sand it down and re coat - again.

 

[RHINO]

i was going to ask what PSI you were spraying at, and the pics look like too heavy a coat.

i dont know what gun you use but i use a LVLP gun and rarely spray over 25psi. regardless i learned its good practice to introduce a light coat first coat , let it flash then come back with the heavier multiple pass coverage coat.

also, regardless what i clean with i always give a final wipe down with isopropyl achohol.

 

[RUSH55]

Way too heavy of a coat the first go ‘round.
Several issues I’ve concluded along with too heavy of a coat were
1) The paint was beyond its “after opening”date
2) The reducer I used was wrong. It is actually compatible with the paint, but I think it was too fast for the ambient temperature
3) The gun setup (2 qt pressure pot and gun with 1.7mm tip) was new to me. I was in a hurry (or in a panic) and didn’t spend any time dialing in the paint volume per minute output or the atomizing pressure. I just went with it, thinking I could knock it down in the color sand and buff stage - WRONGO!

So, the too fast of reducer coupled with too thick of paint coat, I think, produced the porosity.

After some digging I found my mistake with the reducer. When I originally bought the epoxy primer and the urethane paint, I bought separate reducers for each, one of them is compatible with both the primer and urethane, but only used it for the primer. The other reducer was used only with the urethane. Since the last time I sprayed paint was in 2021, I had forgotten which reducer I had used for the paint and got them mixed up. Even though the one I used is technically compatible, I think it’s too fast.

I’m also planning on spending some considerable time dialing in the pressure pot system before letting loose with it again. Going to try to set it up similar to how my HVLP was back when I was spraying in ‘21.

 

[RHINO]

glad you narrowed it down,, i run a 1.3 tip. different guns though so what do i know.

 

[RUSH55]

I think the Binks pressure pot gun I ran the second coat with is 1.3

 

[J Mack]

color sand and buff stage

If you're using the industrial coating from Sherwin Williams you are going to want to skip this step.

(no more than 10% reduction)

To keep your "orange peel" down to a minimum you will need to reduce a bit more.
For a quick "rule of thumb" viscosity check when adding reducer stir the paint and pull the stir sick out quickly and watch the stream of paint coming off the stir stick, when you see the bubbles start to appear on the surface of the paint you should be at a three count, more than a three count add more reducer less than a three count and you'll need to pay attention to not hang a bunch of runs or thicken your mix up before you spray.
It might take a few times to get exactly what I'm trying to tell you but if you try it with your un-reduced paint it should take a six or more count before the bubbles appear then try it with a container of water and it should be under three.

Good luck it sounds like you have figured out the rest of your issues.

 

[RUSH55]

If you're using the industrial coating from Sherwin Williams you are going to want to skip this step.


To keep your "orange peel" down to a minimum you will need to reduce a bit more.
For a quick "rule of thumb" viscosity check when adding reducer stir the paint and pull the stir sick out quickly and watch the stream of paint coming off the stir stick, when you see the bubbles start to appear on the surface of the paint you should be at a three count, more than a three count add more reducer less than a three count and you'll need to pay attention to not hang a bunch of runs or thicken your mix up before you spray.
It might take a few times to get exactly what I'm trying to tell you but if you try it with your un-reduced paint it should take a six or more count before the bubbles appear then try it with a container of water and it should be under three.

Good luck it sounds like you have figured out the rest of your issues.

Thanks Jim.
Something else I discovered this weekend while working on the interior, is that despite having 3 separate air dryers (counting the new big 5 micron dryer/filter) is that there’s still moisture getting through the system. I think water got into the pressure pot and contaminated the paint.

 

[J Mack]

there’s still moisture getting through the system.

Might be time to build a little chiller between the compressor pump and tank, something as simple as some copper line coiled in a bucket of water will do wonders.

Also a “Motor Guard Mini Desiccant Dryer – Dry Air Spray Gun Filter 34146” at the gun will help with the last of the junk in your air lines.