Holding onto paint is a great idea since you can use it for touch ups and a fresh coat. However, over time paint sitting in a garage or shed can separate and become watery on top and hardened on the bottom. There are several ways you can mix old paint to make it useable once again.
How Long Does Paint Last?
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If the paint can is stored properly and has never been opened, it will last for years. Bob Vila states that unopened latex and water-based acrylic paints last up to 10 years, and the alkyd and oil-based can last as long as 15 years. However, if the paint was exposed to extreme temperatures, it may be unusable. If paint was stored in a garden or shed, extreme heat and cold may have taken its toll. If the paint can has been opened, there is still hope. Mix the paint thoroughly for a few minutes with a paint stirrer. Test it out on a piece of cardboard to see its consistency.
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When to Toss It
If you see any white, brown or black spots on the paint surface, throw it away. These spots are bacteria, mold or mildew and will likely spread onto your walls if you use the paint, according to Ace Paints. If there is a bad odor coming from the can, this is also a sign that the can has been contaminated with bacteria. Chunky paint cannot be used. Mix the paint for a few minutes with a paint paddle. If the lumps and clumps remain, then it's time to discard the paint.
Test It Out
Mix the paint with a paint stirrer for five minutes or longer. Try brushing the paint onto cardboard to test it out. If the paint can be applied smoothly, then it is still usable. If the paint comes out grainy or lumpy and cannot be stirred out after several minutes, then the paint needs to be tossed.
Lumps are caused by exposure to extreme temperatures and permanent changes to the paint's chemical makeup, according to Bob Vila. The paint will not come out well on your walls if used. If there is rust from the can in the paint, it is also not usable.
Look at the Can
There are some dangers of using old paint. Look at the appearance of the can. Consumer Reports states that if the paint can is bulging or the lid is puffed up, then the contents have gone bad. The swelling is caused by microorganisms that eat the paint and expel gas. The gas generates pressure and causes the can to inflate. This paint is unusable, and you need to get new paint cans. You don't need to open the can, just dispose of it.
Strain It
You may want to use a strainer to remove any dried paint flakes. There may also be debris, dust or leaves in the paint that you want to remove prior to use. Use a metal mesh strainer and pour the paint over a clean can or plastic container.
Another way to strain paint is by using pantyhose. This is an inexpensive way to remove fine particles from the paint. Ron Hazelton recommends stretching a section of the pantyhose over a bucket and pouring the paint through. The debris will catch on the pantyhose. Make sure they are free of any runs or tears.
Opened Cans
An opened can might still be good. When you open the can, it may have a thick skin on top. This is caused by air exposure according to Bob Vila. Use a paint stick to remove this film completely. After it has been removed, mix it to test out the paint texture.
You can also use an electric mixer to stir paint. Family Handyman recommends a Squirrel Mixer by Homax. It attaches to your drill and mixes paint in a few minutes. It is great for paint separated in a tin where it has solidified on the bottom. It can also be used for mixing joint compound. The mixer is available for purchase at most hardware and paint stores. This method is quicker and more thorough than mixing by hand.
If you find old paint in a color you no longer like or have on your walls, it can be donated. Bob Vila suggests giving it to a local paint contractor or gifting it to family or friends. Some charities accept used paint as well, especially charities that help the elderly with home renovations or other home repair organizations.