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I don’t know where I’d be if I hadn’t decided to finish using a high volume, low pressure (HVLP) system. (From a business perspective, I believe a quality HVLP setup is as important as a quality table saw.) However, today I found out that I’ve been killing my spray gun and I didn’t even know it.
I’ve sprayed barrels of liquid through my guns. Of course shellac and lacquer make up the largest portion, but I have also shot oil-base stains and I can remember one time that I sprayed an oil/varnish mixture onto a cherry dining table (I didn’t have the time to brush on the mixture). All these are solvent-base products, but I also spray water-base aniline dyes and did spray latex paint, once. That happened way back as I first discovered HVLP and since that one time, I have yet to blow paint through any of my guns again.
I’m not a purist when it comes to cleaning my spray guns. I won’t hesitate to leave dye in the gun for a couple days. I’ve been known to leave lacquer in the gun for a few days, too. I’m not alone. One cabinetmaker I know leaves product in his gun for weeks or months on end. However, when I do wrap up the dye process, I rinse the gun with water, push a few ounces of denatured alcohol through the pipes then a bit of lacquer thinner before I move on. When I finish up spraying shellac, it’s a spray or two of alcohol followed by lacquer thinner then the gun goes back on the shelf. I’ve followed this procedure for years because I believed that alcohol encapsulates the leftover water molecules. While that may be the case, I recently found out I am not doing enough.
Somewhere I read that water-base products turn to gunk in the gun , the technical term would be coagulate , and that causes issues when spraying. I haven’t noticed any problems, but I thought it best to check things out. I turned to the group at Apollo Sprayers International, Inc. for answers and in the process, I picked up a tip that could save huge amounts of time if you switch between water-base and solvent-base finishes. John A. Darroch, CEO of the company, put it this way: Water-base materials do not coagulate inside spray guns. However, if you try to use lacquer thinner or paint thinner to clean them they certainly will. There is a chemical reaction between water-base materials and lacquer thinner that makes the water-base materials go gummy and very sticky. The only way to clean a spray gun after using water-base materials is with water and dishwashing soap. Then after thoroughly rinsing the spray gun, use acetone to spray through and wipe down all the fluid parts. Acetone is about the only material besides our Kleen-Again spray gun cleaner that works well to clean-up water-base materials (Kleen-Again is a bio-degradable soybean product available at The Finishing Store). Acetone is a good medium to spray when using the same spray gun with both water-base and solvent-base materials as it dries completely without leaving a residue.
This is a great tip and one I’ll put to use immediately. My spray gun will thank me and I hope to see marked improvement in my spray finishes. If you have HVLP, or some other type of spray capabilities, what do you spray the most? Are you happy with your results? Even if you have a spray system that’s gathering dust in your shop, let me know. Maybe we can get you and the spray gun back on speaking terms.
