That container of half-used latex paint isn't a lost cause just because it's clumpy, chunky or thicker than expected. Thinning the paint, in many cases, restores it to a usable consistency. The best part: Since latex paint is water-based, regular tap water can be used to thin it—no chemical-based thinners required.
Checking the Paint's Consistency
To determine whether that paint is still in good enough shape to use, open the paint container, then stir the paint thoroughly, lifting the stirrer once in a while to check the consistency of the paint stuck to it. Even new paint separates as it settles, so don't judge the paint based on its color or how it looks after a stir or two. Stir the paint for at least a couple minutes by hand, until the color and composition seem fairly consistent throughout. Be sure the stirrer reaches the contents at the bottom of the can, as heavier components settle there. Lift the paint stirrer once again and hold it over a scrap piece of paper or cardboard. A paint with proper consistency will drip evenly. Paint that requires thinning will either stick mostly to the stirrer or eventually drop off with visible clumps or chunks in it.
Thinning Water-Based Paint
Things You'll Need
Old newspapers or cardboard
Clean paint container with -airtight lid
To thin your paint, gather your supplies ahead of time and work outdoors during the day or in an area with sufficient light; this helps you tell when the pigments are properly mixed into the paint. The water-thinning technique works for both latex and acrylic paints, such as common craft paints.
Pour the contents of the thick paint into a clean five-gallon bucket. If you're working with a small amount of paint, such as a quart, a smaller bucket will suffice. Scrape out the insides of the original paint container with the stirrer or a paintbrush to salvage as much paint as possible.
Pour 1/2 cup of warm water into a measuring cup for starters; this much water will thin one gallon of paint. Pour more water into the cup, accordingly, if you're working with more than one gallon of paint.
Slowly pour water from the measuring cup into the bucket containing the old paint. Stir the paint as you work to thoroughly blend in the water. Stop stirring when the paint reaches an even consistency.
Dip the stirrer into the paint once again, lift it out of the paint, holding it over a scrap piece of cardboard. If the paint consistency seems correct or close to it, dip a brush in the paint and brush some onto the cardboard. If the paint coats the cardboard well with no clumps, the paint may be ready to use. Dip the brush a few more times and do a few more test applications.
If the paint still seems too thick, add a few more tablespoons of water per each gallon of paint. It's not an exact science, so stir and test the paint regularly to prevent over-thinning. Paint that still contains solid chunks, clumps, rust or strange discolorations may not be salvageable.
A gallon of paint that has been stored for a long while may be difficult to thoroughly mix again if the pigments and solvents have separated. Your local hardware store or paint store may agree to remix the paint in their power mixer, especially if you are a regular customer.
Prolonging the Life of Latex Paint
An opened container of latex paint can last 10 years or longer if kept at room temperature, sealed in an airtight container.
- To help ensure that paint lasts, use care when opening a metal paint can. A three-in-one painter's tool makes an excellent prying device for the lid. Pry one small area at a time, rotating the lid as you go to avoid bending the lid. Once the lid is bent, it is less likely to close completely again.
- Wipe the lip of the paint can with a rag or paper towel before closing the lid again. This helps ensure the lid can be easily removed without bending it.
- Store opened paint in a more secure airtight container, such as a jar or plastic paint container with a screw-top lid.
- Pour what you need out of the container into a tray or bucket, rather than dipping your brush back into the original paint container again and again. This helps prevent contamination from foreign objects.
- Store your paints out of direct sunlight and moisture, in an area where they won't freeze nor get too hot.
- Label the paint with a dab of the color on the lid, as well as the date it was opened and where the color was used. This helps avoid confusion with similar paint colors.
Kathy Adams is an award-winning writer. She is an avid DIYer that is equally at home repurposing random objects into new, useful creations as she is at supporting community gardening efforts and writing about healthy alternatives to household chemicals. She's written numerous DIY articles for paint and decor companies, as well as for Black + Decker, Hunker, SFGate, Landlordology and others.