Spraying

Spraying is a basic method of paint-application for the modern painter, forming a trinity with the traditional methods of brushing and rolling.

The main benefit of spraying is speed. A two-story house that used to take 10 days to paint with a brush and roller, can be sprayed in 1 or 2 days by just one person. An incredible productivity boost!

Spraying also leaves the finest finish. Anytime paint is applied with a brush, lap marks, caused by the bristles dragging out the paint, are inevitably left behind and visible to the critical eye. Paint applied by a roller leaves behind stippling, caused by the indent of the fibers on the nap. Spraying, on the other hand, leaves behind no visible trace of application. This makes spraying especially ideal when painting smooth surfaces such as trim or doors.

Spraying is also ideal when dealing with non-flat surfaces like furniture. Painting these with a brush or roller is extremely error prone and can take a lot of work to get right. A piece of furniture that takes 2 hours to brush can be sprayed in under 5 minutes!

For an excellent demonstration, see this video.

Airless Sprayers

A paint sprayer, in general, must be capable of three things; pumping, atomization, and patternification.

At its heart, a paint sprayer is a simple pump capable of moving liquid material through a hose at variable pressure. Where sprayers differ is in the process of atomization.

These droplets are then dispersed into the air. However, in order for utter chaos to not ensue, the sprayer must emit the dispersion in a controlled fashion.

Different sprayers emit different patterns. However, most vary on the shape of an elongated oval.

The sprayers that I use are called airless sprayers. They get their name from how they atomize. Instead of pushing compressed air into the liquid paint, like other sprayers do, they use a combination of high pressure and special tips. Thus airless.

The advantage of using an airless sprayer is the ability to output large amounts of paint, making them ideal for large-scale commercial use. Compressed air sprayers, while performing much finer atomization, cannot match the output of an airless sprayer, making them less then ideal for large-scale projects, but more then ideal for extremely fine applications (like repainting cars).

Overspray

Although spraying is incredibly effective and efficient (and my favorite part of painting!), it does have its own set of challenges. The biggest, and perhaps most infamous, is overspray.

Many reputations have been ruined by not taking the proper percautions against overspray. I take the problem very seriously. With care and expertise, it can be controlled.

What causes overspray?

Overspray is inevitable when using a sprayer. Atomized paint reacts with the environment to create an imperfect dispersion. Thus, instead of hoping to eliminate overspray, we can control it by understanding its nature and protecting the places we know it will go.

Controlling Overspray

Understanding your Environment

Paint emitted by a sprayer is dispersed as an atomized cloud. Understanding how this dispersion interacts with the environment is crucial to controlling it.

Since atoms of paint have very small mass, they are easily carried away by the wind. Being mindful of wind direction and speed is the most important concern while spraying. The wind determines the quantity and placement of your masking, as well as determining if it’s even feasible to spray at all.

Another crucial point to realize is that paint atoms have a large surface area relative to their volume. This implies that any liquid inside them will evaporate quickly. The speed at which this evaporation takes place is governed by humidity and temperature. With normal levels of humidity and temperature, it is a fact that most overspray dries in the air quickly enough that it falls to the ground as harmless dust. However, when humidity is high and temperature is low, the dry time increases making overspray more of a threat. In these scenarios, masking must be increased.

Understanding your Equipment

A painter has varying control, via his sprayer, of the following parameters:

  • Amount of paint emitted
  • Pressure
  • Size of the dispersion pattern
  • Size of the paint atoms

Making sure each is tuned correctly relative to the paint being used, the current environment, and the nature of the surface, helps to control overspray by minimizing the amount of it.

Catching

Using one hand to hold the gun, the other hand is free is hold a cardboard shield which can catch overspray that might escape around a corner or under a baseboard.

See here for a demonstration.

Backbrushing

Paint applied with a sprayer exists as a layer on top of the surface. When dealing with highly porous surfaces, like cedar or pine siding, it cannot be expected that the paint will penetrate into the tiny holes and grooves of the surface. Thus the sprayed-paint must be pushed into those pores to guarantee proper adhesion. This process is called backbrushing and is done with either a brush or a roller.

Is it always necessary?

No. If the surface is smooth, then there is no texture in the surface to push the paint into. Backbrushing in this case would both ruin your finish and waste your time.