By Steve Milhoan
In the late 19th century, all painting in the United States was done with a brush. Brushes were used to apply paint on buildings, furniture and many other products. No matter what it was, it took a long time to complete the job.
It was that daunting task that led Joseph Binks to invent the first spray machine to paint walls. In 1887, Binks was a maintenance supervisor for Marshall Field’s department store in Chicago. Marshall Field’s had miles of basement walls that needed to be whitewashed regularly, and when Binks sent a crew down there with brushes and buckets, it was weeks before they finished the walls on a single level of the multi-level basement. In an effort to speed the task, Binks combined a hand-operated pump, a vessel to hold the liquid under pressure and a wand with a nozzle on the end, much like a pump-up garden sprayer. The whitewash was strained into the tank, pumped under pressure by the hand pump and propelled out the end of the wand. With this, the technique of applying paint coatings without a brush was invented.
Today, there are many different ways to manually apply coatings in the finishing world. Below I’ve listed a couple of these techniques and given a brief description along with the pros and cons of each.
Using a paint brush is the least expensive and the most transfer efficient way to apply paint. This way of applying paint is not for anything that requires a Class A finish.
Pros: High transfer efficiency, low equipment cost
Cons: Very low finish quality in regards to gloss, very slow to apply
CONVENTIONAL SPRAY GUNS
Conventional spray guns generally operate under very high air pressures at a 1:1 relation. This translates into a lower transfer efficiency due to such high forward velocity (40 feet per second). This high forward velocity causes a bounce back of material (overspray) off the part you are trying to coat. The benefit of using conventional spray is that it has a high degree of atomization and produces the highest gloss finish.
Pros: Very high finish quality; fast working speed; great for specialty coatings, glues and splatter effect
Cons: Very high overspray, very low transfer efficiency (less than 30% is typical), not compliant with EPA standards
HVLP (HIGH VOLUME LOW PRESSURE) SPRAY GUNS
An important piece of spray gun history is the invention of the high volume, low-pressure (HVLP) spray design. HVLP came to the forefront of finishing techniques in the 1990’s as a response to Rule 1151, adopted in 1987 in Southern California. Air pollution was a problem, so high transfer guns (65% or more) were utilized to reduce smog. HVLP spray guns were designed to improve transfer efficiency. HVLP guns push paint particles at a lower velocity than conventional spray guns. This allows painters to spray closer to the surface so the material actually gets applied to the object instead of floating into the air or bouncing off the object being sprayed. However, paints needed to be reformulated to account for the lack of atomization air. The finish quality of HVLP spraying has an orange peel appearance. It took a long time for “old school painters” using conventional spray guns to switch to this technology.
Pros: Good transfer efficiency (can achieve upwards of 65%), EPA approved, good finish quality once appearance was accepted in the marketplace
Cons: Slower work speed, larger compressor required to run (minimum 15 cfm per gun), lower atomization of coatings, not good for thicker materials
These are just three techniques of manually applied paint. Additional manual paint technologies include: airless, air-assisted airless, electrostatic and LVLP (Low Volume Low Pressure). To learn more about manual finishing techniques and new finishing technologies, contact an OTP finishing and fluid handling expert. We have the technical knowledge and broad product support to help you find the right finishing and fluid handling tools and techniques to achieve all your goals.