Back in the last century, I was on a team developing a wood-finishing short course. A major manufacturer had given us two spray guns to use in our classes and we were testing out some of our procedures with a select group of students who would help us fine-tune the presentations and exercises.
After setting up the guns, preparing panels to be sprayed and familiarizing everyone with the spray booth, controls and equipment, one of the team members demonstrated how to optimize the gun for various spray procedures. Rather, he attempted it. He turned the fluid-adjustment knob to increase or decrease fluid flow and turned the spreader adjustment knob to increase and decrease airflow and adjusted the air-pressure regulator. None of these changes corrected the poor delivery of the lacquer to the surface. These are all things we learned to do earlier in our lives and, in our experience, should have corrected the problem.
So we called the manufacturer’s local technical representative who agreed to meet us later that morning to see what was happening. When he arrived, he tried to spray the gun and immediately turned off the air, disconnected the hose and removed a “cheater valve,” which one of the members had, more or less automatically, attached to the spray gun as part of the setup.
The problem was that the cheater valve allowed adjustment of the air at the entry to the gun by choking down the air passage, which lowered the pressure on the outflow side of the valve when air was moving through the gun. When the air was not moving through the gun, the pressure on the inflow and outflow sides was equal and at the pressure set by the regulator on the compressor. When the trigger was pulled, there was an initial higher pressure burst and then a lower pressure flow as dictated by the valve.
While the use of cheater valves was common on conventional air guns, HVLP guns use a much greater volume of air at very low pressure (10 psi maximum). We had been given HVLP guns. The valve was a more restrictive type that would have been OK on a conventional gun, but would not allow the greater volume of air required by the HVLP, in this case about 12 CFM.
If a similar problem occurred today, I would visit the website of the coatings or spray gun manufacturer for troubleshooting help or use a smartphone app, currently available from Chemcraft and DeVilbiss, for example.
The Internet also gives us greater access to the books and magazines devoted to finishing, though as author Michael Dresdner cautions, “The Internet abounds with shared personal tips that are more homespun myth than proven fact.” Many of today’s blogs, chatrooms and individual websites can lead the unwary astray. YouTube tutorials are good if done right. Generally, an association with a well-known and respected person or company will be safer than the amateur presentations.
Here are some of my trusted sources, beginning with three books for general knowledge of wood finishing techniques, products and problem solving:
“Wood Finishing 2.0,” by Ron Bryze, an experienced teacher and consultant, who gets into the nuts and bolts of finishing, as well as the business side.
“Taunton’s Complete Illustrated Guide to Finishing,” by Jeff Jewitt, owner of Homestead Finishing Products who also shares valuable tips, articles and videos at http://homesteadfinishingproducts.com.
“Understanding Wood Finishing,” by Bob Flexner. This comprehensive guide has been used as the primary textbook for colleges, technical schools, private instruction, industry seminars and more. Flexner’s mission of demystifying wood finishing resulted in this aptly named book, first published in 1998. This second edition (2005) has better photographs and covers recent changes in the wood finishing industry.
Other sources include “The ABC’s of Wood Finishing” that distills the process of wood finishing into a 43-page booklet, covering the selection, use and maintenance of finishing equipment. It is a concise, illustrated guide that should be required reading for anyone in a finishing room and kept handy for referral. I found it valuable when I was first learning “best practices” for wood finishing and it’s been updated through the years by Binks/DeVilbiss. It is now available in a Spanish language edition.
Professional Refinisher’s Group (www.professionalrefinisher.com) is an informal organization made up of restoration professionals. The primary means of communication is a daily, moderated email-based exchange with members posting questions, problems, news, views and replies. I’ve been a participating member since 1998.
Manufacturers’ websites are your best source for updated technical information, product and safety data sheets, videos, application instructions and troubleshooting and maintenance guides. However, while many companies excel at providing this kind of information, others noticeably lag behind.
If you utilize even a few of these resources for a period of time, I think you will be pleasantly surprised at what you can learn.
Other resources include Woodweb (www.woodweb.com); Finishing IQ (www.finishingiq.com); American Wood Finishing Institute (www.awfi.org); Wood Finishing Institute (www.woodfinishing.org); and Architectural Woodwork Institute (www.awinet.org).
And, of course, visit the Woodshop News’ website (www.woodshopnews.com) for archived Finishing columns, new product news and online resource guide.
Greg Williams, formerly senior touchup and finishing instructor for Mohawk Finishing Products, is now a freelance instructor and consultant.
This article originally appeared in the October 2015 issue.