In most areas, waste management companies will not accept latex paint in garbage cans unless the paint is completely solidified. Liquid latex paint can cause huge cleanup problems, especially when the cans are crushed in the garbage trucks and the paint leaks out onto roadways. To do your part for your local city and environment, use paint hardener when you dispose of paint. Paint hardener solidifies leftover latex paint so it doesn't pose problems for your community.
Check the Amount
Cans of paint with less than 1 inch of paint left in the bottom don't need paint hardener to dry out completely. Just leave the can outside with the lid off, and it will dry up within a few days. However, if the can contains more than 1 inch of paint, add paint hardener to help it completely dry. If you have several cans of paint with just a little paint left, combine them in one of the cans, and then add the paint hardener.
Mix It Up
When adding paint hardener to a can of partially used latex paint, first cover your work surface with newspaper so you don't make a mess. Paint hardener usually comes in packets that can be used to harden up to 1 gallon of latex paint. Pour a packet of paint hardener into the can and stir it with a wooden paint stick. Paint hardener is activated by water, so add 1 cup of water to the mixture and stir. Leave the can of paint alone for about 30 minutes. Although it will have a consistency like oatmeal, it will not spill out of the can and is safe to dispose of.
Science at Work
The primary ingredient in paint hardener is sodium polyacrylate, which is a crystallized salt product. The salt crystals absorb moisture very quickly and turn the paint into a solid, rubbery substance. The solid cannot "re-wet," so the paint will not return to its liquid form even if it comes into contact with liquid at the landfill. Sodium polyacrylate needs water to produce this chemical reaction, so paint hardener cannot be used with oil-based paints. Oil-based paints must be taken to a hazardous waste disposal or recycling center.
Paint hardener may cause slight to moderate eye irritation if particles come in contact with your eyes. The dust from the main ingredient, sodium polyacrylate, may also cause lung inflammation if inhaled. Most people will not be affected by the dust, but people with asthma or other respiratory conditions may want to take precautions by wearing a dust mask while pouring the paint hardener into paint cans. Those with sensitive eyes may want to wear protective eyewear while working with paint hardener. Make sure that your bare skin is safe and does not come in prolonged contact with the paint hardener, since it can cause irritation and redness.