Matt is a professional painter and freelance writer, sharing his knowledge, house-painting tips, and product reviews.
Spray Painting Outside and Overspray
One of the fastest ways to tackle exterior painting and staining projects is with a paint sprayer, but one thing you should never ignore is the amount of overspray your spray gun's generating when you pull the trigger.
Depending on weather conditions and the material being sprayed, overspray can travel further than you think and stick to anything in its path, including the neighbor's car if you're not careful.
Paint droplets from exterior paint and stain overspray, especially if it's oil-based, is difficult to remove without causing more damage to the surface it's stuck to.
All paint sprayers emit overspray, some worse than others, and while it's impossible to totally eliminate airborne paint mist when spraying outside, there are several ways to reduce it significantly so you can finish your painting project without any worries.
Don't Spray when it's Humid and Windy
The wind is your enemy when it comes to exterior spray painting. Wind carries airborne paint further away from the spray area, increasing the risk of overspray damage. Spraying when it's windy also wastes paint too because more of it ends up in the air instead of onto the surface you're painting.
Humidity is another important factor to be aware of when you use a paint sprayer outdoors. When it's dry out, paint mist dries a lot faster and turns into dust before it has a chance to stick to anything, but when it's really humid, airborne paint particles linger and stay wet longer. Combine that with heavy winds, or even a swift breeze, and you have a recipe for property damage.
Painting outside in humid conditions is bad for paint anyway, unless you use paint formulated for that. I don't recommend it. If you must paint outside when it's windy, carefully mask the spray area and use the right size spray tip to avoid problems. Move patio furniture out of the vicinity, or cover everything with drop cloths. Make sure windows and anything else nearby that's isn't being painted is covered.
Use the Correct Spray Tip Size
The tip size you choose plays a big role in the amount of overspray during a spray painting project. A common mistake is spraying paint through a tip that's too large and too wide, which results in excessive paint mist and wasted material. Using a tip with a smaller orifice and fan width greatly reduces overspray and eliminates the chances of damaging anything beyond the spray area.
The manual for your paint sprayer should note the maximum spray tip size recommended for the pump. Use that as a starting point. On the back of the paint can too, you will find the manufacturers recommended tip orifice size for the type of sprayer you're using, but try using a tip smaller than what's recommended on the label. The recommended orifice size on paint can labels are often larger than what's actually needed.
Understanding Spray Tip Sizing
My article the Best Graco RAC-X Tips for Spraying Paint goes in depth on airless spray tip sizing and what I use for my projects, but I'll go over the basics on the sizes and understanding the numbering.
Airless spray tips include three digits. The first number is used to determine the width of the spray fan. Multiple the first number by two to determine the fan width. For example, a 315 airless spray tip produces a spray fan that is 6-inches wide (3 x 2 = 6). Let's say you're spraying stain onto deck spindles. For that, using a 315 tip (6-inch fan) is too wide and would spray too much stain between the spindles. The better option is a 115, 112, or a 110, if the deck stain is thin enough.
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The last two digits tell you the orifice size. The greater the number, the larger the orifice, meaning more paint can pass through the hole. Thick exterior paint requires a larger orifice to allow the paint to atomize and pass through the tip without clogging, but don't choose one too big otherwise you'll end up blowing clouds of paint mist everywhere. For siding, a 515, or 517, produce less overspray than using a 519. You could even use a tip with a smaller fan, such as a 417, to reduce the amount of atomized paint in the air.
Use the Right Paint Sprayer for Your Project
I own and use mostly airless sprayers, but I also own one HVLP sprayer from Graco. All of them produce overspray, but the HVLP emits a lot less than my airless sprayers. Airless sprayers are production machines commonly used for large exterior painting and staining projects. They operate at high pressure and therefore produce more overspray than a low pressure HVLP sprayer. My article Airless Paint Sprayer vs. HVLP: Which One's Better? goes more in depth on the differences between the two and which one is right for you.
For a smaller project, such as exterior spindles, a small fence, or staining patio furniture, you can reduce overspray a lot by using an HVLP sprayer instead of an airless, or use an airless with a smaller tip as I explained earlier. Another option is to use a small handheld airless sprayer. These typically run off a battery and spray at lower pressure and work great for small projects.
Turn Down Your Pressure
Spraying at pressure too high results in more overspray and more bounce back, meaning more paint blows back from the surface instead of sticking to it. High pressure is usually unnecessary and wastes a lot of paint. It also increases the chances of paint ending up where you don't want it.
All sprayers have an adjustable pressure control. Pricier models include a digital readout display so you know the exact pressure you're spraying at. My Titan 440 Impact includes a PSI range on the pressure control. My Graco-GX-19 includes a pressure gauge on the sprayer itself. I use that sprayer mostly for cabinets and my Graco Ultra Max airless for most of my exterior spray painting projects.
To reduce airborne overspray, turn your pressure down until the spray fan starts to form tails on the edges of the fan, then turn the pressure up only slightly until the tails are gone. Unless your exterior painting project calls for a fine finish, the only purpose of the sprayer is to get the material onto the substrate quickly. If you're spraying wooden siding, or a fence, the surface is going to be rolled anyway as you spray.
Mask and Use a Spray Shield
Careful masking is critical for exterior spray painting projects. Overspray drifts in the air and can make a huge mess on vinyl siding, windows, patio furniture, or worse, nearby vehicles. When I spray siding, I'll usually ask my customer to park in the garage, or down the street to be safe. Everything in the path of my spray gun is covered with plastic and masking paper. I use the 3M hand masker to make all of my masking quicker and easier. It's a must-own tool for spray painting.
If you're spraying siding, nearby windows must be covered with masking film and tape. Basically anything not being painted in your spray zone should be covered. If you use a sprayer to spray deck spindles, make sure you protect the siding and windows over the deck before you pull the trigger. Move patio furniture to the other side of the yard.
Use a Spray Paint Shield
Spray paint shields are awesome for controlling overspray when spraying siding directly above foundation walls, or to prevent the paint from blowing around a corner. You can also use them to protect shrubbery while spraying, or roof shingles.
Paint shields come as either a full metal piece, typically 20-inches in length, or longer, or you can buy a plastic holder instead and insert a piece of cardboard into it for a shield. I've used both, but the one I use the most is the Warner plastic paint shield holder. I like this holder because I can reuse the cardboard a few times and not have to deal with cleaning off the paint after every use like you would with a metal shield.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Matt G.