How to Clean Vertical Surfaces Before Applying Finish
Vertical surfaces that seem to be in good shape don’t usually require too much washing. A brief, multi-step procedure should take care of things.
To start with, use a Shop-Vac to remove dirt and spider webs. If the surfaces look relatively clean, a brush may be used on some areas rather than a vacuum. Make baseboard trim a target, since it tends to attract all kinds of particles.
Next, combine 1-2 cups of white vinegar, a half-tablespoon of dish soap, and two or more gallons of water. The goal is to make the wash-and-rinse process as simple as basic dishwashing.
Gather some cloths, or other pieces of fabric (such as T-shirts), without lint. Dampen a cloth, squeeze out most of the water, and use it to moisten the vertical surfaces you plan to paint. When the fabric looks unclean, use your soap-and-vinegar mixture to wash it. Keep going until you’ve covered all the surfaces you’ll be finishing.
With clean water and a different cloth, do the whole thing over. This step prevents soap scum from remaining on the walls. Once the surfaces are no longer wet, move on to the next stage of pre-painting preparation.