According to the Environmental Protection Agency, leftover paint is the largest volume material collected by hazardous materials collection sites and costs local governments a lot of money to deal with. The EPA estimates that 10 percent of the house paint purchased each year ends up discarded.
How to Dispose of Leftover Latex Paint
Because latex paint is non-hazardous, it can be disposed of with your regular trash, provided that it is completely solidified or if the container has been completely emptied.
Latex paint has a 10-year shelf life. However, if it has been subject to freezing, it may no longer be usable. First check the label to determine what type of paint you have. Latex paints are non-hazardous and soluble in water - look on the label for the words "latex" or "acrylic" and directions that specify to clean up or thin with water. Test by stirring and brushing paint onto a newspaper. If there are lumps, the paint is no longer good and needs to be disposed of properly.
Remember, one gallon of liquid paint can contaminate thousands of gallons of water, harm aquatic fish and plant life, and eventually, poison the food chain.
To solidify paint, use one of the following methods:
1. Remove the lid and let the paint dry out in the can; protect from freezing and rain as well as curious kids and animals. This method works best when an inch or less of paint is left in the can and is most effective in warmer months.
2. Mix latex paint with an equal amount of cat litter, stir in completely and allow to dry.
3. Mix latex paint with a latex paint hardener; stir and allow to harden. Paint hardener can be purchased at your local hardware store. Follow the directions on the package.
4. For larger volumes of latex paint, line a cardboard box with a plastic bag. Add an absorbing agent such as kitty litter, sawdust or shredded newspaper to the box. Pour the paint into the box so that it forms a thin layer (about 1 inch deep) and allow the paint to harden. Repeat this process until all of the paint has hardened.
Once the latex paint has hardened or solidified, it can be disposed of with your regular trash. However, when you set them in your garbage can make sure the lids are removed from the paint cans. If paint still leaks out you need to dry it more.