Paint is usually custom mixed. Even if you have the formula, there are no guarantees that the color of a new can will be an exact match to your previously painted surfaces. The best insurance for a perfect match is to save the leftover product. There are steps that can be taken to extend the shelf life of your remaining paint. Here are some tips.
Before you start
• Do all preparations of your work area before opening the can.
• The paint stores usually do a good job of mixing the product when you buy it. Depending upon the quality of the paint, no stirring is necessary if it is being used within 24 hours of purchase.
• Remove the lid carefully with a paint can opener. Attempting to pry the can open with a screwdriver or other tool may distort the lid, making it difficult to create a good seal when you are done.
During your project
• Exposure to air is what makes paint harden. Minimize the number of times you open the can. Do not leave it open while you are painting.
• If you need to stir the paint, do it gently so additional air is not introduced into the product.
• Pour paint into a small container or roller pan. Clean the well (the indentation around the top of the can), and replace the lid.
• In the event your latex paint is too thick, take out the amount you will need and place it in a separate container before adding water. If you add water directly into the can, the remaining paint will spoil prematurely or mold will form. Discard any diluted paint.
When you are done
• Before closing the can, clean the lid and the well of excess paint.
• Excess air will cause paint to dry prematurely. Place a piece of plastic wrap inside touching the top of the paint before replacing the lid. This will prevent a surface film from forming.
• If the can is less than half full, consider transferring the remaining amount into a smaller container so there will be less air inside the can. They are available at most paint and hardware stores. Or, you can use any type of container that will maintain a tight seal (such as a Mason jar).
• Use a rubber mallet to tap the lid shut for a tight seal. If using a hammer, place a piece of wood on the top so the hammer doesn't distort the lid.
• If your paint is in a plastic container, clean the threads along the sides and inside of the lid. Then coat them with a small amount of petroleum jelly to create a good seal.
• Label the lid of each can with the name and number of the formula. Also include the room where it was used and the date it was purchased. For quick reference, put a dime-sized drop of the actual paint on the top. This will eliminate the need to open the can any more than necessary.
Where to store paint
• Store remaining paint in a climate-controlled environment. Freezing will render paint products unusable. Likewise, excessive heat will make it react with the excess air in the container and cause it to thicken.
• Do not leave paint cans on a concrete, stone or tile floor. The moisture will cause the can to rust over time and will distort the color.