Spraying vs rolling: paint usage, overspray and finish

Where the paint goes

When you roll a wall, almost all the paint ends up on the wall. A little stays in the roller cover, the tray and the bottom of the can: about 5% is a fair allowance. When you spray, a fine mist of paint misses the surface or bounces off it and drifts away. That overspray is paint you bought and did not use, and it depends on the conditions far more than on the sprayer.

These are site estimates, in line with the transfer efficiencies our film thickness calculator uses: about 70% of the paint reaches the surface from an airless sprayer, 90% from a roller and 95% from a brush. The loss divides rather than adds, which is why the column on the right grows faster than the percentages suggest:

The spray versus roll calculator applies these losses, and the film thickness calculator uses the same idea under the name transfer efficiency.

The difference in gallons

On a small fine-finishing job the gap is proportionally bigger: 180 sq ft of cabinet faces at two coats is 1.08 gallons by roller and brush and 1.71 gallons sprayed, because the fine-finishing loss is the highest.

Where the time goes

Spraying is fast. Our production rates put an airless sprayer at about 600 sq ft an hour on walls against 200 for a roller with brush cutting-in; on the 1,000 sq ft example, that is 3 h 20 min of spraying against 10 hours of rolling. But the spraying is only part of the job:

• Masking. Everything that is not being painted must be covered: floors, windows, doors, trim, fittings, furniture. On an occupied interior, masking for a sprayer can take as long as rolling the walls.
• Setup and cleanup. Priming the pump, straining paint, flushing the hoses and gun at the end, and cleaning the filters. On a first job this can take as long as the spraying.
• Back-rolling. On rough surfaces and many exteriors, a second person rolls the wet sprayed paint into the surface, which improves adhesion and evens the texture.

The result is that spraying wins clearly on empty new construction, exteriors, large open areas, ceilings and anything with lots of detail, such as fences, railings and louvred doors. It often loses on a single furnished room. The painting time calculator compares the methods with prep and setup included.

How much paint goes through the gun

For a larger job, the airless sprayer usage calculator works out the paint, the refills and the spraying time from the tip’s flow rate:

Choosing the tip

The tip sets the flow and the width of the spray fan. A 517 tip, common for interior latex, has a 0.017 in orifice and a 10 in fan. Thicker paints need bigger orifices; thin stains and lacquers smaller ones. A tip too large for the pump will not hold pressure, and a worn tip sprays a heavy-edged fan and wastes paint. Airless spray tips explained decodes the numbers, and the spray tip calculator picks one for your paint and pump.

Thinning for spraying

Most modern airless sprayers handle latex unthinned, and many paint data sheets say not to thin for airless application. HVLP sprayers, and some smaller airless units, need thinner paint. If you thin, stay within the label’s limit, often around 10%: 12.8 fl oz of water per gallon. Thinning lowers the film thickness per coat, to about 91% of the unthinned film at 10%, so hiding suffers. The thinning ratio calculator works out the mix.

The finish

A sprayer, well used, gives the smoothest finish of any method: no roller stipple and no brush marks. That is why it is the standard for cabinets, doors and furniture. On walls, a sprayed finish can look slightly different from a rolled touch-up later, which is why some painters spray and then back-roll walls, so that future touch-ups with a roller blend in.

HVLP and other sprayers

Not every sprayer is an airless. HVLP (high volume, low pressure) sprayers atomise paint with a large volume of air at low pressure. They are slower than an airless and usually need the paint thinned, but the soft, controllable spray gives a very fine finish, which makes them popular for furniture, cabinets and doors. Our film thickness calculator uses 65% transfer for HVLP as a default; transfer depends heavily on the gun, the paint and the operator, so use the gun maker’s figure if it gives one. Pump-up garden-style sprayers are used for stains and sealers on fences and decks; they lay on a wet coat that is usually brushed in. For walls, ceilings and exteriors, airless is the standard.

Which method for which job

Spraying ceilings and texture

Textured and popcorn ceilings are where spraying is at its best, because nothing touches the fragile texture and every hollow fills evenly. Textured and popcorn ceilings covers the coverage and the extra paint.

Safety

Airless sprayers work at pressures high enough to inject paint through skin, which is a medical emergency. Never point the gun at anyone, never put a hand in front of the tip, keep the tip guard on, and engage the trigger lock whenever you stop. Wear a respirator suited to the paint, and eye protection; spray mist travels further than it seems.

Common mistakes

• Planning spray quantities from roller coverage. Add the overspray.
• Counting only spraying time. Masking, setup and cleanup are most of the job indoors.
• Spraying outdoors in wind. Overspray drifts onto cars, neighbours and plants.
• Turning up the pressure to fix a bad pattern. Replace the worn tip instead.
• Thinning past the label limit. The paint spreads further and hides less.
• Skipping back-rolling on rough exteriors. The paint sits on the surface instead of in it.

The production rates behind the time figures are explained in painting production rates.