How long should you let spray paint dry? It varies depending on the paint, and you should always read the can to get specific advice for the paint you’re using, since my favorite brand might be different from yours. But generally speaking, an hour is the absolute minimum.
A more realistic minimum safe drying time for spray paint is about 8 hours. Some hobbyists let their paint sit and cure for a full week before they assemble the item and put it into service, and they’ve had excellent results with this practice. Your can is your guide, because dry times can and do vary. So always, always check the instructions on your can. But here are some general guidelines.
How long to let primer dry before spray painting
Ideally, it’s best to use primer unless you’re painting plastic and using plastic-bonding paint. More on that in a minute. And if you’re painting metal, consider self-etching primer. Primer helps the paint to adhere better for a stronger, more durable finish. It also makes it easier to paint the top coat because it’s less likely to run or drip.
It’s also best to match brands between primer and topcoat. You can mix brands, but not under all circumstances, so if you plan to do that, experiment first to make sure the two don’t react.
Drying time with primer varies, but many modern primers are ready for the topcoat in about an hour. Check the can to make sure, but frequently primer is ready that fast, so it doesn’t add terribly long to the length of time it takes to complete a project. And the results are worth it.
The argument against primer
In the old days, no one used primer. So some people don’t use primer today for the same reason. The difference is that in the old days, paint had lead in it to help it stick better. Seriously, that was one of the main reasons for putting lead in paint. Today’s paints don’t have lead in them, for very valid safety reasons, so that’s why we use primer to compensate. Even if it increases dry times.
Extreme dry time for those with the patience of saints
I know someone who lets his primer dry a full week before putting the topcoat on. He says he gets a more durable finish that way, and I believe him. But when you do that, you run a greater risk of dust or other spots marring your finish. Wipe your work down with a tack cloth before you apply your topcoat if you let the primer dry that long.
Keep the piece indoors at room temperature during the drying period. You don’t want it outdoors exposed to the elements if you can avoid it. Either put the piece on a jig so you can pick up and move the whole jig without touching the piece, or let the piece sit in place for about an hour before moving.
If you want the extreme strength that comes from extreme dry times but without waiting a week, I have a trick for that near the end if you can hang in there with me that long.
Choosing a primer
I find I get best results when I use a primer color that’s close to the color of the top coat, if at all possible. Primer generally comes in gray, red, green, white, or black. If you use a color that’s closer to your topcoat, you won’t need as much paint to cover it, and so it will dry faster and you’ll be happier with the results.
Primer and plastic-formulated paint
There is one exception to my primer rule. If you’re painting plastic and using paint that’s formulated to chemically bond to plastic, such as Krylon Fusion, you don’t want to use primer. In that case, the primer will interfere with the paint bonding to the plastic. It will still work, but you’ll get better results applying plastic paints straight to the plastic.
If you need to paint plastic and the color you want isn’t available in a plastic-bonding formula, you can try using the plastic-bonding paint as a primer instead. Try to match brands and use a color that’s reasonably close to the top coat in color.
How long to let spray paint dry in between coats
Generally speaking, you get a better paint job if you apply multiple thin coats. Thick coats take longer to dry and are much more likely to produce runs and drips. Applying thin coats works better and dries faster because the previous coat helps the next coat dry itself. When you apply a thin dusting, it tends to stay in place because there isn’t enough volume of liquid for it to run or drip. Each subsequent dusting stays in place too, as long as you let the first coat of spray paint dry just enough.
The dry time between thin coats is short. With many paints, you want to apply a thin layer, let it dry, then apply a second thin coat before an hour has passed. Repeat as necessary. If you miss that hour window, you need to wait a full 24 hours before applying another coat.
I generally find 30-45 minutes isn’t a bad length of time to wait. Sometimes I can get away with as little as five minutes, if the coat was thin enough. But that’s pushing it. If you want to be really, really safe, wait about 50 minutes. That’s close to the maximum, while leaving you a little bit of margin for error.
Also, when you spray in thin coats, you can make subsequent coats progressively thicker. Don’t get in too much of a hurry. But you can add a little more and get the job done faster without too much risk of runs and drips.
How long to let spray paint dry when you’re finished
Some paints claim to dry to the touch within an hour, and to be dry enough to handle within 4 hours or even less. That’s usually pretty optimistic. It’s much better to let the paint dry at least overnight if you can, and a full 24 hours, regardless of what the can says. That same guy who lets his primer dry for a week lets the topcoat dry for a full week as well before he handles the piece. He moves the piece indoors and keeps it at room temperature during that drying period.
Let the piece sit where you painted it for at least a couple of hours if at all possible before you pick it up and move it indoors.
If you have to move it sooner, make some kind of a jig to hold the piece so you can pick up the jig without touching the piece itself.
Accelerating the drying process
I’ll share a trick a lot of old-time train restorers used. They accelerate the drying process by making an oven. To do this, get a wooden box, put a light socket for an ordinary household light bulb in it, then put an incandescent bulb in the socket. Then use a cooking thermometer (you could also use an infrared thermometer) to check the temperature inside after letting the bulb warm up the box for about 30 minutes. You don’t want it to be too hot. Around 120 degrees Fahrenheit is about the maximum you want so you don’t scorch the paint. You can adjust the temperature by playing with the opening of the lid. Open the lid further to decrease the temperature. If your item is plastic, you probably want to max out at 100, or just let it sit at room temperature.
Put the piece in the warm box, away from the bulb so it’s not bearing the full brunt of its heat. Let the piece sit to dry in the warm box for 24-48 hours, and that’s about equivalent to letting the paint dry for a week at room temperature.
How heat accelerates the paint drying process
The speed of chemical reactions doubles every 10 degrees Centigrade you raise the temperature. So if room temperature is 21 degrees Centigrade, and you raise the temperature to 50 degrees Centigrade (the equivalent of 120), you cut a 7-day drying time down to 21 hours. If you can only reach 40 degrees Centigrade (the equivalent of 100 degrees Fahrenheit), the drying time will be closer to 42 hours.
Now no one can say I don’t remember anything from high school chemistry.
Don’t use a kitchen oven to dry paint!
As tempting as it may be, don’t use your kitchen oven for this. It’s a bad idea to mix industrial processes with food preparation. You don’t know what ingredients are in the paint that will linger in the oven afterward. Plus, I can tell you it smells really bad when you do it.
How do I know? I have an old toaster oven I use to dry items that are small enough to fit inside it. I only used it in the house once. I’ve used it in the garage ever since that little mishap. Fortunately I was the only one at home that weekend when I tried it.