How to Add Thinner to an Oil-Based Stain

Gather your oil-based stain and paint thinner on a work surface covered by a tarp to protect against spills that can be difficult to remove. Have a measuring cup and scraps of wood ready for testing or prepare to test on less visible areas of the wood surface you plan to paint.

Open your first can of stain and add small amounts of thinner from the measuring cup, noting how much is being added each time. Continue until the stain is thin enough for good application, but not so diluted that it has lost its ability to darken wood. Each time you add thinner, test the stain on scraps of wood or less visible parts of the painting surface until you're satisfied with the result.

Pour the same measured amount of thinner into all of cans of stain as you open them for use. Make sure you mix the same ratio of thinner to stain for each painting surface; not doing so will create uneven shades in the finish. Use a stick to stir the stain regularly.