Spray Painting

 

Although brushing and rolling are the most efficient methods of transferring paint from the container to the surface, spray painting is the most cost efficient method of applying paint . . . particularly on large flat surfaces.

Why is spray painting so cost effective?
In most painting situations, time or labor is the biggest and usually the most expensive factor.  A good rule of thumb to remember is that labor cost is 10 or more times the cost of the typical architectural coating being applied.  Anything that aids in getting the job done faster will usually result in lowering the overall cost.  Spray painting gets the job done faster and, in many instances, better than brushing or rolling.  When applying fast drying coatings, such as lacquers, it is indispensable.

Are there more efficient ways to apply paint?
Earlier we mentioned that brushing and rolling are the most transfer efficient methods of paint application.  That is, very little paint is lost or wasted during the application process.  However, these are labor intensive methods of application.  Conventional Spray . . . a term referring to paint applied using a compressor and cup (or larger closed container) of paint has a transfer efficiency of about 50%.  That means that 50% of the paint is delivered to the object being painted.  The remainder is "over-spray" that misses the target.  Over-spray does constitute a small economic loss of paint.  It may also create potential health problems and often disfigures adjacent areas.  That's why we offer drop cloths, dust masks and spray socks (hoods) to protect nearby objects and the person using the spray equipment.  Despite the seemingly low transfer efficiency, a lot of surface can be covered in a relatively short time making spray painting a cost efficient paint application method.

If Conventional Spray has a 50% transfer efficiency, are there other methods of spray painting that are more efficient?
The new HVLP (high volume low pressure) technique transfers up to about 80% efficiency.  Airless Spray has a transfer efficiency of up to 65% and electrostatic spray transfers paint up to 95% efficiency.

How does spray painting work?
The basic principle of spray painting, including D.I.Y. aerosol spray painting, is the same.  Regardless of the method, paint is delivered to a spray tip.  When the trigger is engaged, the paint stream is broken into a fine mist (also known as atomized) that will coat any object in its path.  The tip does the atomizing . . . either through high fluid pressure as is the case with aerosols & airless spray . . . or, in the case of conventional & HVLP spraying, through the use of air pressure.

What, specifically, is Conventional Spray?
Conventional Spray uses compressed air (usually from an air compressor with an air reservoir tank), a spray gun, and a container for the paint.  For smaller jobs, or for jobs requiring frequent changes, the paint is put into a cup that attaches to the fluid passage of the gun.  From there, the paint is siphoned up to the nozzle by the vacuum created by the flow of air.  For larger production, the paint may be placed in a separate closed container which is connected to a pressure source with one hose and to the spray gun with another hose.  The paint is forced up to the gun by air pressure.  The paint is broken into a fine mist when it passes through a small hole or orifice in the spray tip on the gun.

How does Airless Spray differ from Conventional Spray?
There are two major differences between Conventional and Airless Spray.  The first is delivery pressure.  With Airless Spray, the paint is "pumped" to the tip under sizeable pressure ... usually in the range of 1,000 - 2,500 pounds per square inch (PSI).  Whereas with Conventional Spray, the pressure on the paint in the pot or cup is around 5 - 10 PSI.  Second, with Conventional Spray the paint is atomized "externally" of the tip.  That is, the "horns" on the spray tip break up the paint stream.  Air under a pressure of 15 - 35 PSI is introduced to the paint stream through the "horn holes" of the air cap.  With Airless Spray, the paint is under so much pressure when it leaves the spray tip it figuratively "explodes" into thousands of small particles. 




How important is tip selection and maintenance in Airless Spray painting?
Tips determine the spray pattern, control the flow of the coating being sprayed and ultimately tell the pump how hard it must work.  When beginning a project, choosing the right tip size and fan width will determine how profitable a painter will be through both coating consumption and production time.  If the tip size being used is wrong - by either choice or through wear - mil thicknesses will be too heavy and the finish will be unprofessional.

The reversible tip technology is relatively new and is what a high percentage of painting contractors are using in today's market.  The reversible/switchable tip are tips that can be reversed for quick and easy cleaning.  They are also easy to remove when you want to change to a different size.

How does high volume low pressure (HVLP) differ from Conventional and Airless Spray?
HVLP is a relatively new approach to efficiently applying lacquers and other high quality enamels with minimal over-spray.  HVLP combines the low pressure and cup gun application of Conventional Spray with flow rates closer to Airless Spray.  The flow or delivery volume ranges from 50-175 cubic feet per minute and the equipment operates at pressures of 3 - 8 PSI.  The units are "self-contained" with high quality air filters to help deliver cleaner paint jobs with less over-spray.
What is Electrostatic Spray?
Electrostatic Spray involves charging the paint with electricity while grounding the object being painted.  This technique is often used in manufacturing situations - oftentimes called product finishing.  It may also be used in on-site repainting of office furniture.  Equipment requirements include special spray guns or other machines for applying the electrical charge.  The system utilizes a potential of roughly 100,000 volts applied to the atomized wet particles of paint.  The paint is attracted to the grounded object and will actually turn in the air and collect (also known as wrap) onto the surfaces of the work farthest away from the spray gun.  In addition, as the film builds to an even thickness on the object, the conductivity at each point diminishes.  This results in a more uniform coating.

By the way, since Airless Spray is the largest market for paint application . . . next to brushing and rolling . . . ALLPRO has a private label line of Airless Spray Equipment and HVLP Equipment.