Airless and air-assisted airless spraying

Overview

Airless sprayers use a pump to force finish through a small tip at high fluid pressure, which breaks it into droplets without air. Air-assisted airless (AAA) does the same at lower fluid pressure and adds a little compressed air at the tip to refine atomization. Equipment dealer Bolair says neither is better in general: airless is quicker and suits primers, heavy paints and protective coatings; AAA gives a softer fan with less tailing and is preferred for cabinetry, doors, millwork, trim and furniture. This is a professional-shop technique; most hobbyists should start with Spraying with HVLP.

When to use

• Whole kitchens, doors and trim packages where HVLP volume is too slow but finish quality matters (Bolair).
• Thicker coatings that need heavy output, where Fuji notes HVLP at under 10 psi would force thinning.
• Not for one tabletop; pumps, tips and cleanup are overkill, and the results demand operator skill (Bolair stresses that setup, tip choice and technique matter as much as the machine).

Materials and tools

• Pump and gun: airless or AAA. Graco's FinishPro II is described by the maker as handling demanding materials without thinning and with less overspray, and as switchable between AAA and pure airless.
• Tips and filters sized for the coating; Bolair says compatibility depends on coating, tip size, filtration and the sprayer's pressure range.
• Sprayable finishes only as the finish maker specifies; check the technical data sheet. For example General Finishes' Arm-R-Seal data sheet says spraying is not recommended, so verify first.
• Masking, a booth or well-ventilated room, respirator.

Steps

1. Read the coating's data sheet for sprayability, tip and thinning.
2. Choose the system: standard airless for primer-type coverage; AAA for the visible fine finish (Bolair).
3. Fit the recommended tip, strain the finish, and prime the pump.
4. Test on scrap. Set fluid pressure as low as gives a clean fan; with AAA add air to soften tails.
5. Keep the gun square to the work, overlap passes, and keep moving. Bolair says overlap, tip selection and pressure are still needed even on airless.
6. Spray thin and even; follow the maker's recoat times and see Build coats and sanding between.
7. Flush the pump with the maker's solvent immediately after use.

Common problems

• Tails and heavy edges on airless fans: pressure too high or worn tip; AAA reduces tailing (Bolair).
• Too much overspray in a small room: lower the pressure or move to AAA or HVLP.
• Runs and sags, orange peel: see Troubleshooting finish defects.

Safety and environment

Follow the equipment manual, which covers high-pressure fluid hazards, and wear a respirator and eye protection. Flammable finishes need ventilation and no ignition sources. See Oily rag safety.

Related

• Spraying with HVLP: lower-pressure alternative.
• Thinning and viscosity: viscosity targets.
• Water-based polyurethane, Pre-catalyzed and post-catalyzed lacquer: typical sprayed coatings.