Spraying paint and other finishes works best within certain temperature and humidity ranges — about 65 to 75 degrees F, and humidity at about 50 degrees.

With some parts of the United States experiencing high heat, when other parts are already on the way to winter freezes, this article covers tips for successful HVLP spraying at both extremes — and for storing your spray system and gun if you decide not to spray for a month or more.

colorful map of average fall temperatures by U.S. state — Fall Average State Temperatures, courtesy of CurrentResults.com

Note that the more powerful your HVLP system is, the more able it will be to produce fine results in weather extremes. This is especially important if you have trouble cooling and warming your indoor spray area, or need to spray outdoors. So a Fuji Q5 spray system will be your best bet if you can afford it, and the T70 bottom-feed cup, or a pressure pot, will make it easiest to heat and cool the fluid if need be. (See the Fuji Spray 3005-T70 and the 2-quart and 2.5-gallon pressure pots.)

If you want to store your system and spray gun:

Note that these same procedures apply even if you are storing your system and gun for a month or two while you go on a trip!

Don’t let your HVLP equipment freeze! Store it in a clean dry place, preferably above 45 degrees F. Remember that cold weather condensation can cause rust.

Store the spray gun with the lid off the fluid cup, to make sure any spray fluid or solvent evaporates completely.

Clean the spray gun completely, and lubricate the air cap needle.

This is an ideal time to send your spray gun in for cleaning

If you bought your Fuji Spray system from me, you may still have an unused coupon for a free ultrasonic cleaning of your spray gun. If not, an ultrasonic cleaning costs $59.95, plus any parts needed for repairs and for the replacement of consumables such as a pressure tube. Details on Spray Gun Cleaning page.

or give your spray gun a thorough cleaning yourself:

HOW TO SPRAY IN COLD WEATHER

Winter Average State Temperatures, Courtesy of CurrentResults.com

keep the finish and turbine and spray gun warm

In cold weather this is crucial. Spraying a surface that’s too cold can cause blistering and other problems in the finish results. If the turbine and spray gun are too cold, condensation can form in the air lines.

Indoors, aim at keeping the spraying and drying area between 65 and 75 degrees F. The minimum is 50 degrees. Halogen lighting adds some heat.

Pay attention to warmth in the drying area, as finishes that dry too fast or too slowly can cause problems.

Users report using blankets and even electric blankets and heating pads to do the warming. Just be careful of sparks, obviously, when spraying solvent-based finishes.

SPRAYING OUTDOORS IN COLD WEATHER

Keep your paint, turbine, and spray gun warm except when you go outside to do the actual spraying.

If at all possible, wait for a sunny day, and spray in the warmest part of the day.

Pay attention to the dewpoint. This is when condensation will start to form on the surface before and as you paint it too early, and form on the paint surface before it dries, if you paint too late in the day.

Pay attention to both day and night highs and lows. Don’t paint outdoors if the 24-hour low temperature falls below 40 degrees. The exception is for paint that the manufacturer specifies for temperatures as low as 35 degrees F.

Protect the painting surface from wind as much as possible. Use a spray booth or set up plastic wind barriers.

If you’re painting more than one side of a building, follow the sunlight around it so you take advantage of the warmth of the sun.

tips for spraying in either weather extreme: cold or hot

Colorful U.S. map of average summer temperatures by state — Average Summer Temperatures by State,
Courtesy of CurrentResults.com

indoors, USE A DEHUMIDIFIER TO KEep humidity in ideal range.

Set the dehumidifier range to hover around 50 percent. A reasonable range is 45 to 60 percent humidity. To avoid having to empty the water bin more than once a day, choose a dehumidifier with a gravity drain or even better, a pump option.

Remember that night time humidity is important too. Most finishes take some time to cure completely, so maintain a good range of humidity even after doing the actual spraying. If a finish cures too slowly because of high humidity, it can become less durable. Latex paint may never coalesce properly.

indoors or out, Check the temperature of the surface you’ll be spraying.

If it’s a flat horizontal surface, you can use an inexpensive surface thermometer. The handheld infrared surface thermometers are more versatile and need not cost much. You want the surface to be between 50 degrees F and 75 degrees F.

In hot weather, you may be able to spray in higher temperatures, but keep in mind that as heat rises, paint and other finishes that dry too fast and leave streaks on the final finish. The finish may not be as flexible and durable.

Consider wind and exposure to sunlight.

Wind or drafts on the surface you’re spraying can cause finishes to dry too fast, causing problems in the resulting finish. A pop up spray booth can help both indoors (if your room is drafty) or outdoors. You can also rig up plastic wind and draft barriers. These also keep dust and insects from getting stuck in wet finish.

Outdoors In cold weather, use sunlight to help warm the surface. In hot weather, use shade to keep the surface from getting too hot. If you’re spraying a building outdoors, consider the order of painting the building sides, to take advantage of shade in summer, sunlight in winter.

check the recommendations from the finish supplier

The temperature and humidity ranges may be printed on the finish can. If not, the paint and varnish suppliers can tell you what to aim for, and provide information on how much longer a full curing will take if temperature is too low, and/or humidity is too high.

The finish supplier may also advise you on using a larger air cap in hot weather or

Finishes may need extra thinning in hot weather

The finish supplier may provide details on this, and sell extenders custom-formulated to work well with their brand. Otherwise, consider Floetrel for extending latex and acrylic paints.

You can adjust the speed of spraying

Remember to test adjustments on a test piece!

Since cold and low humidity each speed drying, you can slow it down by any of these methods:

thinning and warming the finish in the fluid cup,
using the smallest air cap that will work with your finish,
adjusting the fluid control on the spray gun to limit paint flow to a finer spray,
and if you have a Q5 or Mini-Mite 5 system, by lowering the air pressure from the turbine. (The new D6 system also lets you adjust the turbine air pressure even faster.)

When the temperature and humidity are so high that your finish dries too fast for good blending, you may also need to thin the finish and even cool it down. Note that the faster your turbine (the higher the stage), the faster you can spray. A 5-stage Fuji Q5 system will spray over 4 times faster than a 2-stage Fuji Semi-PRO. (See “How to Choose an HVLP System” for details.)

You can speed up the spray by any of these methods:

cooling the finish in the fluid cup,
adjusting the fluid control knob on the spray gun for faster fluid flow,
using a larger air cap — increasing the size by one or two sizes,
removing the filter on the bottom of the fluid tube and instead, filtering the finish into the fluid cup through a paper or stainless steel cone filter.

Consult the Fuji Spray manual for your system and spray gun too.

More information on choosing the best air cap setup for your finish.

Good resources for spraying paint in heat or cold

Consumer Reports has a good article on spraying water-based paints outdoors, based on their own paint tests. Highlights include:

Make sure the surface and ambient air are at least 50 degrees F, and that the nightime low will be above 32 degrees, preferably above 40 degrees.
For spraying in cold weather, look for paint that the manufacturer specifies can be painted in weather as cold as 35 degrees.
This may seem obvious, but if the surface you’re painting in hot weather is uncomfortable when you place your palm against it, it’s too hot to paint.

Homestead Finishing has a detailed guide to hvlp spraying paints: latex, acrylic, and oil-based. https://homesteadfinishingproducts.com/wp-content/uploads/2014/04/paintspraying_ver3.pdf

Additional detailed weather information by state and city is available at CurrentResults.com. You can also get weather information about other countries at that site.

feel free to ask me for advice on your specific weather and spray project

Call me at 800-377-5662, M-F 9-5 PM CT — or email me at roger@phelpsrefinishing.com.

Happy spraying!

Roger Phelps, owner (and the one who answers the phone).

HVLP Spraying in Extreme Cold and Heat