While acrylic latex paint can be used right from the can with no problem, thinning it does help with workability. Some varieties of this paint can actually vary in thickness depending on the finish, flat, satin, or semi-gloss, and on the quality, and the brand. The thicker the paint, the more it lends itself to catching and keeping dust and debris that can ruin the appearance of your finish. So, save yourself some trouble by spending a little extra time thinning out acrylic latex before you grab a brush.
Difficulty: Very little; a novice can do this.
Time: It should take about 10 to 15 minutes to bring acrylic latex paint to the proper consistency to apply.
When Is the Paint too Thick?
Before starting this task, you need to be sure that thinning your paint is the right step to take. A too-thin consistency is just as problematic one that is too thick, as thin paint will run and drip and potentially ruin your trim in the process.
Stir the paint in its container with a stirring stick, and then hold it above the surface to watch how the paint runs off. If it drips like water, then the paint is already too thin and you have a bad batch, but if it comes off in globs, then continue with thinning as intended.
You can also use a funnel to test if you have one handy. Scoop up some paint into it and let it run through. If it has difficulty emptying, then the consistency is too thick and you can proceed.
Adding the Thinning Mixture
To properly thin acrylic latex paint, add about two to three ounces of water per gallon, depending on the starting condition. After adding a small amount of water and mixing it in, see if that is the consistency that you want it to be; add more water if necessary. Always start with a small quantity of water since it's easy to keep adding a little at a time. On the other hand, if too much is added, nothing can be done to reverse the amount.
To mix the water into the paint, use a stirring paddle in an upward and downward spiral motion. You can also pour the paint and water back and forth between the original container and an empty one-gallon can.
Tip: Do not use paint additives. They are generally not needed and have little effect on the paint or its application.
Edward Kimble, a professional painter and author of Interior House Painting Blog, contributed to this article.