Latex or water-based, paint is often used to paint interior walls or furnishings that are not exposed to the elements. Latex paints can thicken sometimes when not used and may need to be thinned out before you can start painting. Follow the tips below to prevent the thickening of your paint and learn the best ways to thin water-based paint if prevention fails.
1. Avoid Leaving the Paint Can Open
One of the easiest ways to avoid the thickening of your water-based paint is to simply close the lid on the can when you finish pouring paint into a bucket or roller pan. Leaving the lid off of the paint can too long does allow moisture to evaporate from the paint, which will, in turn, make it thicker. So, as soon as you pour your paint, close the paint can.
Tip: Also, a slight covering of water on the surface of the paint is great for keeping the paint from thickening too much as you let it sit. Pour a small amount of water very slowly on top of the paint in the can. If you pour it in too fast, it will just mix with the paint.
2. Don't Store Latex Paint Too Long
If possible, try to avoid storing latex paint too long. Over time, water-based paint will begin to thicken as the moisture evaporates and its consistency will become much harder, even putty-like.
3. Keep Stirring
If you've been unable to prevent your paint from getting thick, it will take some work to make it usable again. Fortunately, it's not hard work.
When allowed to sit for a long time, latex paint will decant, with the heavier particles settling to the bottom. Before trying to thin the paint, stir, stir, and then stir some more. The more you stir your water-based paint, the smoother it will become. If you have a drill, consider purchasing a paint mixer extension to make the process easier and more efficient. The electric drill stirring rod is very sharp. Insert or remove the stirring attachment with the electric drill unplugged.
When stirring your paint, keep in mind that stirring the paint for only a minute or so usually won't mix the paint well. If you're stirring the paint by hand, stir the paint continuously for at least five or 10 minutes.
You'll want to stir in an upward and downward spiral motion to mix it well; however, the best way to thin and stir latex paint is to pour the paint back and forth between two paint cans.
Tip: Also, when using more than one gallon of custom color, you should pour the paint back and forth repeatedly to mix the paints. This is called ‘boxing’ the paint and it will make your color more consistent between cans since custom colors are known to vary slightly with each mix.
4. Use Water to Thin Water-Based Paint
If stirring isn't enough and you do need to add liquid to your water-based paint to thin it out, try using water before adding anything else.
Add an ounce or two of water to the can and then thoroughly stir. Continue to add water in small increments until the desired consistency is achieved. If you add too much water at the start, you will find that a lot of time will be needed to thoroughly mix the paint, so remember, add a little, then stir a little. Continue the process until the paint consistency is just right.
5. Use a Commercial Thinning Additive
There are several different commercial products available for thinning water-based paint. If you look in the paint section of a local home improvement store, you will find products that can be added for thinning. These commercial additives are advertised to help to thin the paint and also act as a paint conditioner, making the paint easier to apply and helping to remove unsightly brush marks. Although these types of commercial additives can be effective, they are also expensive. So, try adding water first. Also, once such additives are put into a can of latex paint, the paint has a very short shelf life.
If, after all this, your paint is too far gone to use, it's best to just throw it out and start with a new can. In this case, make sure to dispose of it properly.
Edward Kimble, a professional painter, and the author of "Interior House Painting Blog" contributed to this article.