Dirt in the Finish

      Troubleshooting a problem where pieces being finished with conversion varnish seem to attract dirt and dust out of nowhere.July 16, 2012

About eight months ago we switched from precat to cv. Since then we have had problems with dirt in the finish that we can't figure out. We've cleaned the finish room and added a filter wall with twenty furnace filters to clean the incoming air. My finisher has tried wearing a clean suit. We've tried different guns and pumps, used the shop vac on the surfaces instead of blowing them off, and we've tried different brands of finish. We have filtered the finish and repeatedly changed filters in the guns and pumps (they weren't dirty). We've also had finish reps try to identify the problem. The booth and pumps are grounded and we've tried many other things and just can't get a clean finish. Does anyone have any ideas?

Forum Responses
(Finishing Forum)
From contributor P:
What happens when you switch back to your old finish?

From contributor L:
Sounds like static electricity to me. Try pouring some of your finish onto a clear pane of glass and let it dry, this will tell you if the finish has any debris. If the poured material looks fine, spray some onto a clean pane of glass. If that looks fine, spray some onto a board you have prepped for finish and wiped down with alcohol.

If the sprayed onto board looks fine, try it again on a board that you have prepped but not wiped with alcohol. If this board has debris, you have a static problem. If this started eight months ago when you switched from pc to cv, what else changed? Low humidity is the usual suspect for static charge and adding a humidifier to the finish room will make a difference.

From contributor G:
I have the same problem. I can get a perfect finish using MagnaMax, MagnaKlear and Stealth but as soon as I start spraying Krystal I get a dirty finish. I have played the DNA game. It helps a little, but that is it. If I sprayed two of the exact same things using MagnaKlear and Krystal I would have a perfect finish on the MK and a dirty finish on the Krystal. I rarely use Krystal because of this.

From the original questioner:
We noticed right away that CV required cleaner everything. Just before quitting time today I talked about this again with my finisher. He said it is worse now that it is colder. Itís consistant with the static theory. We had suspected static but dismissed it because we do have very effective humidification in the shop.

As I was reading the replies to this post it dawned on me that the humidity isn't making it into the finish room. The makeup air enters the shop all the way on the north end which has a partial wall separating it from the rest of the shop. The air then draws into the finish room which is also on the north end. This airflow pattern does not allow humidity to enter the finish room. I am going to move one of the humidifiers to the north end tomorrow. Hope it works.

From contributor U:
Are you sure it's not tiny air bubbles? That will make your finish look and feel dirty. I went through the same thing thinking I was getting dirt in the finish, and it turned out that it was just a gun setup issue. Try lowering the air pressure - CV's don't like much air. Also try a little flow additive.

From the original questioner:
We have had the tiny bubbles (solvent pop) also. We cured that with pressure and film thickness adjustments. We definitely also have dirt, sometimes both. They do look different from each other. Our intial lay down is also good. If we stare at it for a few minutes we notice dirt starting to appear. Some of the dirt looks like little tiny strings. It seems to magically appear from nowhere. That's why we are suspecting static.

From contributor G:
Not bubbles for me - definitely dirty.

From the original questioner:
Contributor G - Are all the products you mentioned conversion varnish? Precat seems to stay cleaner for us but I want more durability.

From contributor G:
No, most of the others are precats. Stealth is a pigmented conversion varnish. If I could get a clear Stealth I would be happy.

From the original questioner:
Do you notice the problem worsens during low humidity? I am in the Midwest, and we have low humidity now that it is cold outside so it seems worse for us.

From contributor G:
I use them so infrequently that I really have nothing to compare to. I did wipe everything down with DNA twice before spraying to help with the static. My AAA is grounded and I have an isolated filtered spray room.

From contributor U:
Have you sprayed Klearvar? My ML Campbell rep told me Stealth is a pigmented version of Klearvar.

From the original questioner:
Our problem seems to be fixed. I think it was a combination of many things. Air and fluid pressure adjustments, cleaning better, added humidity, slightly thicker coats sprayed down, and other minor things.

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