If you have an outdoor painting project on your to-do list, you might be watching the weather report to determine the ideal day to get it done. Yet if all you’re watching for is a day without rain, you’re not paying close enough attention to the weather report. That’s because temperature and humidity can have significant effects on paint as it’s drying, and none of them are good. Even if there’s no rain in the forecast, painting under conditions in which temperatures and/or humidity are too extreme can mean all your hard work could wind up being for naught. With the average house painting project costing about $3,000, that’s an expensive failure. If it’s a commercial or industrial painting project, you likely can multiply that sum several times over, depending on the scope of the project.

Whether the paint is oil-based, latex or acrylic, it is a liquid. That means moisture must be able to evaporate out of it at the proper rate in order for it to dry properly. Temperature and humidity can wreak havoc on this process for various reasons, which results in more than just having to wait longer for it to dry. Paint that dries too slowly or even too quickly won’t adhere as well to the surface, with the result being ugly imperfections and premature flaking or peeling.

For example, painting when temperatures are too hot could mean that the top layer of paint dries and skins over, well before the layers beneath it have a chance to dry. That means the top layer of paint is in danger of literally sliding off the wall. At the very least, the dried top layer of paint will be pulled down by gravity and the paint will dry in waves of uneven thickness across the entire surface. This can lead to blisters, cracking and peeling — even before the paint is dry. On the other hand, painting when temperatures are too low can create other problems. Moisture in the paint may crystallize before it has a chance to evaporate, causing imperfections in the paint, for instance. Most oil-based paint needs to be applied at temperatures above 45 degrees Fahrenheit, while latex and acrylic paints must be applied at temperatures above 50 degrees Fahrenheit.

Because the moisture level in paint is so important to drying properly, humidity can upset the balance and ruin a day’s work. Most importantly, high humidity can re-introduce moisture into the paint as it dries, lengthening the amount of time it takes for the paint to dry and increasing the risk of imperfections. Additionally, excess moisture in the air can be absorbed into wood surfaces and hurt the paint’s ability to adhere to them. Humidity also has the potential to cause compounds in the paint to be leached out of it, creating patches of discoloration.

There’s more to be concerned about before starting an outdoor painting project than rain. Not paying attention to extreme heat, cold or humidity can spell disaster for a painting project if you’re not aware of what they can do. Before you get started on your next painting project, review the accompanying guide and understand how temperature and humidity can become big problems for paint.