Calcium Contamination in a Spray Finish

A finisher gets advice on addressing what appears to be a white calcium buildup on his spray system's filters, which is contaminating his work. November 29, 2014

Question (WOODWEB Member) :
We are spraying water-borne clear topcoats on mostly maple veneer plywood. We are experiencing some contamination that is resulting in what look like small fisheyes. Cleaning the gun did not help. So we looked at our air supply. We have a 5 micron inline filter on the tank output. It does catch some water. Since the air can be hot at this location, and carry more water vapor, we also have two filters just before the last 25 feet of hose line leading to the gun. The first of these two is another 5 micron filter. It does catch a fair amount of water depending on the weather. Immediately after this we have a 0.01 micron coalescing filter. Its job is to collect any remaining water and oil vapors. It does catch some water.

We have depended on the red/green indicator on the top of this last filter to determine if it needs servicing. It is still green. We decided today to internally inspect the filter cartridge for no obvious reason other than we still have contamination. What we found surprised us. There was a heavy build-up (up to 1/2" thick in places) of what appears to be calcium on both sides of the filter cartridge. At least it looks like calcium. However, we are used to seeing calcium build-up from the local water supply on and around faucets. The air compressor is not connected to the water supply, so this is puzzling.

We have ordered a new filter cartridge for the coalescing filter. We have cleaned out the filter housing. It is not perfect, but the heavy build-up is gone. We have flushed out and brass-brushed the housing quite well. We are also replacing that last 25 feet of hose line leading to the gun. We don't think there really is a good way to clean it. For less than $40, it is less expensive to simply replace the hose instead of risking a recurring problem. My questions are: has anyone had any experience like this? Or, does anyone have some ideas on what that residue was? Or, why it was on both sides of the filter cartridge? We do not have anything scheduled for the finishing department for the next few days. The replacement filter cartridge and new hose line should arrive before we do. Hopefully, by early next week, we will know if this resolved the contamination issue. We are still curious on how this happened. By the way, we have noticed that the drain on our vertical compressor tank is not draining much, if anything, for the last month or two. The tank dates back to 2006 and is located indoors. If there is an accumulation of this same white stuff inside the tank, how would we clean it?

Forum Responses
(Finishing Forum)
From contributor T:
First thing is clean your tank and drain daily.

If the tank isn't draining like it should:

- Purge air from system
- Remove drain valve or pet cock
- Depending on drain style open manual drain on bottom of tank.
- If you have a bucket level drain then there is a hose leading from that going down into the bottom of the tank. These clog constantly.

- Wash out drain hose until clean.
- Replace hose making sure it is going into bottom of tank.

I would bypass this system by putting a valve and garden hose on the bottom of your tank so you can easily drain the tank daily. This is the first thing you need to address and the most important thing. If your tank is full of water you will always have issues. I had the same problems in the past and found this to be the main culprit.

My new system uses in this order an after cooler, oil separator, 150cfm fridge air dryer, water separator, in line dryer and final filter at both booths. Even with all this equipment we still get some moisture is we don't drain the main tanks daily. If you get your tank cleaned an running properly and have your new filters installed and still have issues then pick up some inline desiccant filter that you can place right at your gun as a last line of defense. The ones I used in the past were an orange color and I got them at a local auto body store. Before setting up my new system I had them on the inlets of my kremlin and gracos and on the gun air inlet as well. They change colors when they go bad.

From contributor C:
Get yourself an electric drain valve for your tank - it costs about $200. You can program them to drain however often you need. Itís one less thing to forget to do. Itís also very helpful when it is very humid.

From contributor D:
It might not be a contamination issue at all. Are you thinning out your product? Is the first coat heavy? I was getting the same problem years ago. I started adding two-three oz. of water per quart and waiting 10-15 min before spraying. Water base clears and water need time to sweat unlike lacquers. First coat is a tack coat to break surface tension. The next coat is a thin wet coat but evenly covering the surface. By spraying in this method I have zero reaction and less grain raising issues. Any water that can get through your filters wonít contaminate your mix because it already has water in it. This has worked flawless for me - I hope it solves your problem.

From contributor S:
My thought about contamination before the filter is that something is coming from the compressor. Where is it getting its air for the pump? I would look at the color of and level of the oil, has it been changed? Are the air filters ok for the pump? You may need to go to a refrigerated style dryer. Itís pricey but they do work wonders.

From contributor K:
A while back we had fisheye problems and went crazy trying to figure it out. It turns out there was a guy across the street that was detailing cars that caused the problem. He had a pressure washer that he used to wash the cars and the water in the tank had a silicon solution in it. The small particles of siliconized water would get sucked into the booth right past the filters and caused problems. Once we got him to stop spraying that stuff out there the problem went away and never came back.

From contributor L:
The residue you are seeing - are you using aluminum fittings or filter housings? If so, the white residue could be aluminum oxide (white rust) generated from the interaction of water and the metal surface. Again, if so, simply make sure you flush and clean as any particulates becoming loose will result in this effect seen.