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Airless spray painting

Airless spray painting Posted on 14 April 2022

airless spraying

Airless sprayers are a fast and cost-effective way to apply high-quality coatings. In the first of a three-part series, we look at how to get the most from your airless spraying equipment.

Airless sprayers might seem like a new concept, but rest assured that you most likely use a form of airless spray system every day – your bathroom shower.

In airless spraying, the fast moving, high-pressure liquid stream provides the energy necessary to overcome the fluid’s viscosity and surface tension to form a fine spray – ideal for flawless paint jobs.

In an airless system, fluid is pumped under high pressure through a spray tip, with the tip size and pressure determining the material flow rate. The tip also creates the fan pattern. Airless is in contrast to air spray systems, which inject compressed air into the fluid stream of a fluid such as paint to achieve atomisation.

Why go airless?

Airless sprayers provide an easy and economical way to apply coatings no matter the amount of solids present. Indeed, professional painting contractors prefer to use airless sprayers for three key reasons:

Speed: Airless spraying is up to four times faster than brushing or rolling, enabling more jobs to be completed in less time, and reducing labour costs.

Quality: Airless sprayers produce an even coat of paint on all types of surfaces, leaving a high-quality finish. 

Versatility: Airless sprayers can be used for a wide range of coating materials, including interior and exterior jobs, and can easily be transported from job site to job site.   

Top tips

While the fluid section, pressure controls and power sources are important components of airless sprayers, if one refers to the pressure controls as the ‘brains’ of the system, then the airless spray tip is definitely the heart of the system. An airless spray tip helps determine the fluid flow or the amount of coating applied, and determines the spray pattern (i.e. fan width). All Graco airless sprayer tips are made from the highest grade of tungsten carbide, the most abrasive-resistant material used for airless spray tips. 

Selection of the correct tip is essential to maximise productivity, as the tip determines the fluid flow and the size of the spray pattern – the fan size. Using the right tip results in maximum control and minimum overspray, which means faster work and less paint usage, which ultimately means finishing the job quickly without wasting paint.

When choosing the right spray tip you need to consider several factors including the material thickness, the sprayer’s maximum flow rate and the best fan size for the job. It is also important that you know when a tip is worn and needs replaced.

Spray tips are rated in terms of litres per minute (lpm). Before determining which tip to use, the following factors should be considered:

The sprayer’s maximum flow rate

For optimum performance, the sprayer must have a maximum flow rate higher than the flow rate of the tip, so be sure the flow rate of the tip is less than the maximum flow rate of your sprayer. For example, a 15 thousandths tip (.015) has a rating of 0.91. Hence, the sprayer must be capable of pumping at least 0.91 lpm. Why use a tip with a lower flow rate? When the tip wears, the orifice becomes larger, and the flow rate increases.  

The thickness of the material

It’s easy to determine which tip size to use when you know the type of material you’ll be spraying. Lower viscosity (thinner) materials, such as stain or lacquer, require a spray tip with a smaller orifice or hole size. Heavier materials, like latex, require a tip with a larger orifice. Extremely heavy materials like elastomerics and blockfiller might require spray tips larger than .035.

The best fan size for the job

Fan size – the width of the spray pattern – determines the area covered with each pass. For a given tip orifice, a wider fan delivers a thinner coat, less defined spray pattern, more overspray and faster coverage on broad, open surfaces.

A narrower fan delivers a thicker coat, more defined spray pattern, less overspray and better control when spraying small or confined surfaces. To maximise productivity and reduce labour costs, choose a tip with the right fan size. In general, a larger fan size increases production with less control, and a smaller fan size decreases production with more control.

Choosing your airless sprayer

There are many factors to take into consideration when choosing the correct airless sprayer for an application:

Material and surface to be sprayed 

The types of materials you spray will determine the size of the tips you use. If you plan to spray a variety of materials you have to consider buying a sprayer with greater versatility. Will you be spraying on dry wall, exteriors or concrete? You have to consider the tip sizes needed as well as the quality of finish required in order to choose the best sprayer for the job. Each job has its own requirements. New construction, residential work and commercial jobs vary in terms of coatings used, crew size needed, and power source available.

Litres per week to be sprayed

Purchasing a part-time sprayer to do a full-time job has disappointed many contractors. In the long run, saving money on a sprayer that is inadequate for the job, or not durable enough, will cost a lot in lost labour.

Using more than one spray gun

If you plan to use more than one gun at the same time, then you have to purchase a unit that has the ability to handle multiple guns.

Hose lengths necessary

Hose length depends on the job site, material being sprayed, tip size and hose diameter. Your sprayer must be able to support the length of the hose. Most Graco sprayers use DC motors, which are able to support longer hose lengths than either AC or universal motors.

Available budget

Buying a sprayer is an investment. You don’t want to over-buy or under-buy. Keep in mind the saying, “You can pay now or later”. Downtime resulting from an undersized, overworked sprayer or poor-quality equipment can quickly wipe out any savings from the initial low purchase cost of the sprayer.  

Look out for part two of this feature in the summer 2022 issue of Decorating Matters. Discover Graco’s range of airless sprayers at