Acrylic paints are sold both in artist-size paints and in paint cans used to paint homes. This type of paint has a lengthy shelf life, and problems with rust, mould or debris generally occur because of improper storage or deterioration of the paint containers. Some paint is now being sold in plastic containers, which may reduce contamination of paint. Extending your paint life depends on how soon you notice problems.
Acrylic artist paints have a shelf life of up to 7 years. On average, most manufacturers suggest replacement after 5 years. To help your paints stay fresh and usable, you can take a few precautions. When opening your paint tubes, always clean the exposed threads on both the tube and inside the cap. This may take a few seconds, but this simple trick can help prevent air from leaking into the closed and capped tubes.
Press acrylic paint up from the base of the tube and clamp the tube with a tube clamp that applies even pressure across the tube. This helps reduce pockets where air can build up inside the tube to cause paint problems. The common problem for most acrylic paints is the build-up of mould. If you see mould, remove the mould and throw the mould away. Don't add water to your artist paints. After finding mould, add a few drops of ammonia to the container to prevent future mould.
Acrylic house paint has an equally long shelf life if the can remains unopened and stored in a dry, cool environment. Most acrylic house paints suffer from incorrect storage. When you open the paint can, try not to distort the lid or lip of the can. Clean the lip and lid thoroughly before closing the can. Tap the lid onto the can using a rubber mallet. Use the following pattern: top, bottom, right, left, rotating the can as you tamp to seal the lid as tight as possible.
If you notice your paint cans are starting to rust on the outside, it is likely they are starting to rust on the inside too. Purchase new, empty cans from the paint department of the home improvement store. Place cheesecloth over the new can so that it dips into the can. Secure the cloth with a rubber band. Remove the lid on the old can. Place a second cheesecloth over the old can and secure it with a rubber band. Pour through both layers of cloth to remove as much of the debris in the paint as possible. Secure the new lid on the new can and label the can properly. Allow the old paint to harden inside the open can and dispose of it properly.