Tutorial On Airless Spraying
Author: Bill Rice

Before we begin, my bias should be noted. If there is any way you can spray the project with a compressed air sprayer (especially HVLP), DO IT. If you need the speed and extension capability of an airless, get a AIR ASSISTED airless sprayer. If you have to rent the equipment, you're going to find most equipment rental locations will either give you a funny look or tell you they have an air assisted airless when they don't have a clue what one is.Airless sprayers are DANGEROUS pieces of equipment when not used in COMPLETE compliance with all the equipment manual's instructions. Make sure you get one from the rental location and READ it completely before even thinking about using it. Having said that, a regular airless sprayer will rent for anywhere from $65-$100 per day for a .4 gallon per minute model. Or, you may already have one. This tutorial is ONLY about spraying and will notcover operating the pressure controls, cleanup or troubleshooting anything but the spray. Now to begin.

To cover large surfaces quickly, admittedly there is nothing better than an airless paint sprayer. The type of coating possible to be sprayed is determined by the tip size of the spray gun. Tip and motor size will dictate the speed of coverage capability. For our clear coats, a .11 or .13 tip size should work fine. But, remember, what you gain in ease and speed, you give up in transfer efficiency. The typical conventional compressed air sprayer will transfer 30-35% of the material!it sprays onto what is being sprayed. A typical airless sprayer will transfer 35-40%. The newer air assisted airless sprayers are capable of 50-60% efficiency as well as a "softer" fine finish like a HVLP compressed air sprayer that will transfer from 65-75%. A turbine HVLP can get up to 90% . If you're spraying a high performance coating like ours, costing up to $200 per gallon or more, every 10% you increase transfer efficiency will save you about $20. Ease of maintenance, quality of finish and transfer efficiency are all reasons we prefer HVLP compressed air sprayers.

If you are thinking of buying an airless, you would be well advised to try and get an air assisted one. These units,have a small compressor built in that supplies low pressure air to the air cap (which is where material exits the gunand the spray pattern is created.) Unlike regular airless that can spray at up to 3000 psi, an air assisted can spray at500-750 psi.

All airless spray systems atomize the coating by forcing the fluid through a small orifice at high pressure. Airlesssprayers provide pressure from either a diphragm or piston pump unit driven by an electric, gasoline, or air poweredmotors. Some models use a hydraulic driven pump powered by electricity or gasoline power. Basically, on all models, material is drawn into the fluid tube by the piston on the up stroke, from a pickup tube immersed in thecoating container. On the down stroke, it forces the coating thru the hose and out the spray gun.

The hose is an important part of the system. By its expansion and contraction, the hose will provide "volumetriccushioning" (sort of like a fluid filled shock absorber) allowing the fluid a steady paint flow at the tip. The hose alsoconducts static electricity build up back to the sprayer where it can be grounded.

Some advantages of airless painting systems are:

• Cover large surfaces fast
Faster than brush, roller or compressed air sprayers (although speed would be very close on surfaces easily accessed from the ground)
• No need for an air compressor to spray
• Wand extensions increase the vertical surface that can be sprayed from the ground

Airless Application Techniques

Here are some basic guidelines on airless spraying that should produce an acceptable paint finish. Most are the same as for compressed air sprayers. Obviously, do NOT swing the gun in an arc like movement.. You always hold the gun perpendicular to and an equal distance from the target surface Move the gun either across or up and down the surface at a steady rate and consistent speed. Practice this with a piece of cardboard to get a uniform wet coat without any sags or runs. Always practice moving the gun (without triggering it) over the surface prior to actual spraying. Spray alternately in left to right and right to left strokes (or up and down; then back and up strokes in the vertical).

Remember, always be mindful of starting the movement of the gun BEFORE pressing the trigger and release the trigger before your spraying motion stops. The 95% spray in between the start of the motion and end of the motion will contribute greatly toward the uniformity of the coating. The guidelines for the distance from the spray guns tip to the surface you are spraying should be somewhere between 9-12 inches. But, experiment to determine the right distance for you.

If you are using too large a tip, the result will be runs or sags. Change to a smaller tip. Conversely, if the tip is to small the coverage may appear too thin. Change to a slightly larger tip. But, always remember, you want a pattern that is UNIFORMLY wet from top to bottom or side to side. The proper overlapping of the spray pattern is also important. You can experiment; but, usually a 20-25% of the width of the pattern overlap is about right. Don't be afraid to experiment when first determining the correct size tip. Or, speed, distance or overlap for that matter. A few minutes with testing and experimentation will help assure a fine looking job.