You can never buy just the right amount of paint. There is always some left, but not enough for another project. At that point you have to decide if you want to store just in case you need that color for touch ups or if you just want to pitch it.
There are some possible solutions to consider before you decide to throw it out. Paint will store for quite a long time if it is sealed properly and kept at the right temperature.
One suggestion is to cover the paint can with plastic wrap first and then secure the lid on tight with a hammer to ensure it doesn’t dry out or get lumpy. It needs to be stored in a cool place, but not below freezing, and out of the sunlight and reach of kids or pets.
Some people think they might need a little paint in case a chair bumps into the wall and scratches off the paint or makes a divot in the drywall but in this article, they are more practical about keeping old paint:
Who Knew? : What Should You Do with Leftover Paint?
When you’re finished painting, you might tell yourself you need to keep all your old paint in case you need to do a touch-up. But you should know the paint on the wall (especially if it’s in the sun) will fade in only a matter of months. So, that half-full can of leftover paint probably won’t match the color on your walls—you’ll have to repaint the entire room from scratch for an even job. However, it might be worth saving a small amount for a very small area, like a nick or scratch. We like keeping extra paint in a clean shampoo, conditioner, or body wash container. It will keep away the clutter of old paint cans, while keeping the paint fresh. If you need to use some, just dispense it onto a paper plate and get painting! How to Keep Used Paint Fresh
Find the full post here: Who Knew? : What Should You Do with Leftover Paint? :: Quick and Dirty Tips ™
Make sure you label any paint that isn’t being stored in the original container, as suggested above, or you will have wasted all of your time. Include the date, where it was used, and any other pertinent information from the label on the can of paint.
One thing to keep in mind is that oil-based paint is more toxic than latex paint, so that might also be a factor in how you decide to dispose of the paint.
If you choose to not keep your paint, there are rules in most states about throwing it away. One way around that is to let the paint dry out before you toss it.
This article gives some good tips on how to go about that task:
How to Throw Away Paint – Disposing of Hazardous Materials
Dry it out before you throw it away. Wet latex paint can be hazardous, so dry it up. If there’s only a small amount of paint in the bottom of your can, leaving it out in the sun should do the trick. If there’s a bit more than the sun can handle, try adding kitty litter or newspaper to help soak up the paint and speed the drying process. For larger amounts of paint, purchase a paint hardener at a home improvement store for just a few dollars. Check your local laws, but in many locations, you can throw away dried-out paint with the rest of your household trash.
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If all else fails, there are quite a few states that have recycling programs that allow you to drop off paint and then it is revamped into a usable product. States like Oregon are quite progressive but also have strict laws about not properly disposing of paint or other hazardous chemicals.
This video offers some great tips for what to do with leftover paint and donating it is one of their suggestions. Organizations such as Habitat for Humanity are willing to take paint that might otherwise go to waste.
Check out their other ideas for how you can manage unwanted paint:
The organization they mentioned is called PaintCare.org and they have a page that allows you to enter your Denver zip code to find a paint recycling location near you. You can also search for a hazardous waste drop-off facility in your area at Earth911.com.