While the U.S. Environmental Protection Agency (EPA) does not classify latex paint as hazardous waste, most waste disposal facilities will not accept wet paint of any kind. Extrapolating data from several states, the EPA calculates that between 35 and 103 million gallons of paint are disposed of each year. Commercial waste paint hardener can be expensive and difficult to find. There are several homemade solutions and strategies for quickly drying out paint and legally getting rid of the old paint cans cluttering your garage or basement.
Homemade Waste Paint Hardener
The less paint in the can, the quicker you will be able to harden it--this goes for what you can put in at home as well as commercial paint hardeners. If you have several cans of waste paint, some containing just a little and some full, divide the paint up so they all have about the same amount of paint in them. Put them somewhere warm and dry, with the lids off.
One of the most efficient hardeners is clay-based cat litter, which is extremely absorbent. Use a partially filled paint can as a dustbin for used kitty litter. The paint will quickly form a dry skin; the underlying paint will take longer to dry. Speed the drying process by leaving a paint stirrer in the paint can. Stir it daily to break the skin and allow the rest of the paint to air dry.
If you do not have a cat, any absorbent, dry material will work. Try vermiculite, soil, potting soil, dried leaves or pine needles, dry lawn clippings, even shredded newspaper.
Contact your trash company and ask what its waste paint policy is. Commercial paint hardeners do not completely dry the paint out, although they speed the process. They will turn paint into a sticky, semi-solid consistency that is acceptable by many trash companies. Other companies, however, require paint to be completely dry before they will take it.
Alternative Ways to Harden Paint
If hardening the paint is impossible--as in the case of spray cans--use it up. Spread layers of newspaper on the ground and empty the spray can by coating the newspaper. Let it dry, crumple it up and put it in the trash. If you are in a hurry or have many full cans of paint to get rid of, pour the paint into any wide-mouthed waste containers you can think of. Coffee cans, milk jugs with the tops cut off, even cardboard boxes lined with plastic bags. Protect the ground or floor when you are doing this. If the leftover paint is fairly shallow in the containers---about an inch---it will dry within a day as long as the air is not humid.