Flat wall paint normally dries to a low-sheen finish. This sheen helps to conceal slight wall imperfections. Satin paint, however, contains more gloss than both flat and eggshell finishes, and walls are easier to wash as a result. If you have flat-sheen paint that you want to convert into a satin finish, you can mix it with higher gloss paint, such as semigloss, to get an intermediate finish. However, according to the North West Paint and Supply, flat paint is a course grind product that requires thorough mixing to ensure a uniform finish.
Purchase a gallon of compatible paint in a semigloss finish. For example, if you have flat latex interior paint, you should use semigloss latex interior paint. It's important to mix paints with compatible resins.
Pour half a gallon of the flat paint into a clean bucket and mix thoroughly with a large stir stick. Use a bucket that is at least 1 gallon in size.
Pour half a gallon of the semigloss paint into the flat paint. Stir thoroughly to get a uniform finish. Apply the first coat to your project in a light, even brush strokes.
Wait for the paint to dry and check the sheen level you created. If you are not satisfied with the finish, pour more semigloss paint into the bucket to further increase the sheen level. Thoroughly mix the paint and apply in even coats.
Thorough mixing is necessary to create a uniform finish when mixing flat paint with higher-sheen paint.