Whenever you use spray paint, you’re creating a small cloud of paint particles. This cloud can settle on nearby surfaces, coating everything in dust or still-wet paint. This undesired migration of particles is called overspray, and it’s a nightmarish issue in many different industries.
For example, here’s what a slow-drying enamel paint can do to an innocent garage floor:
Fortunately for us, paint overspray is relatively easy to deal with. I recommend painting outside, then letting your object dry inside. Painting outside carries a lot of benefits (fumes quickly disperse, etc), and drying inside keeps the bugs and dust off your tacky wet paint. However be aware that wind can carry paint many yards, so don’t paint anywhere near cars, windows, or other high-value items.
If you absolutely must paint inside, I recommend using lots and lots of plastic sheeting. Paint can’t pass through plastic, so buy the thinnest (and therefore cheapest) sheets you can find. Also paint in small bursts, and check surrounding exposed surfaces to ensure they aren’t getting coated. Finally, open as many doors and windows as possible, to maximize ventilation.
Overall, overspray can cause some serious issues, but is also easy to avoid as long as you plan ahead.