Do You Need to Clean Walls Before Painting?

Cleaning walls before painting
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Paint manufacturers always say that you clean interior walls before painting. Recommended is trisodium phosphate (TSP), an inexpensive white powder that you mix with water to produce a mild cleaning solution.

As with so many products today, this recommendation ranges from sound remodeling advice and a statement created to limit company liabilities.

But do you need to do this? Are there any instances when you can get by without cleaning walls before painting?

Bottom Line

Cleaning Needed Cleaning Not Needed
Walls are excessively dirty, oily, or greasy Walls that are relatively clean
Children or pets in the home Ceilings
Bathrooms and in kitchens around stove and sink Low impact rooms (i.e., bedrooms)

When You Can Avoid It

If you have a normal house, low-impact rooms, usual activities—you do not need to scrub with TSP when preparing to paint.

Common themes:

  1. Lack of excessive dust.
  2. No Crayon, grease, or other substances on the walls that paint refuses to stick to.
  3. No wood-burning fireplaces.
  4. Little or no contact with the skin.
  5. No pets.
  6. No cooking or bathing (thus, bathrooms and kitchens are excluded from this class).
  7. Walls, not horizontals like baseboard or door trim tops.

Areas That May Not Need Cleaning

True, lightly washing with TSP is always preferable to not lightly washing with TSP. Simply put, clean is always better. 

But if a full wash-down is preventing you from tackling the painting, then you should skip the wash.

Test to Determine If You Can Skip the Wash

At what level of uncleanliness can paint adhere properly?

Today's paints have greater tolerance levels for sticking to surfaces that are less than perfectly clean.

Take a dry white-colored cloth (cloth, not a paper towel) and run it across the wall. Run it the entire length of the wall. If you can turn the cloth over and the color ranges from white to light-gray, you can skip the wash.

You should run it the length of the wall (at least 15 feet) as a control factor. For instance, even if you have an extremely dirty wall, running the cloth just a foot or two may not produce any color on the cloth, leading you to believe that the wall is clean enough.

Interior Painting Prep, Minus the TSP

If you skip TSP cleaning, then at least do the following:

  1. Remove the Big Stuff: Knock down the "dust bunnies" and cobwebs with a broom or vacuum.
  2. Trim and Baseboards: Use a lightly water-moistened cloth and run it across the tops of door and window trim and baseboards. These places will have significant amounts of dust. Cleaning them will help the painter's tape stick.
  3. Vacuum: With the bristle attachment on a home or shop vacuum, clean floor areas near the walls.

Priming your walls is also one way to encourage paint to adhere to the walls better without cleaning first.

Washing Alternative: Pole Sanding

Professional painters hate washing walls. There are many good reasons for this. For one reason, they're not in the business of washing—they're in the business of painting. For another reason, washing cuts into painting time, which cuts into their income. 

In short, do not expect your professional painter to wash down all of your walls. He is not being lazy; he is being practical.

However, you may find your painter pole-sanding some flat surfaces with fine-grit sandpaper. This sloughs off sticky dirt and junk; deglosses surfaces; and knocks down some of the stipple.

If you're insistent on having him wash down all walls with TSP, expect to pay extra for this service Better yet, hire a cleaning person to do this before painting.

When You Need to Wash With TSP

You should keep TSP on hand as an addition to your collection of essential painting supplies. We would use TSP in the following instances:

  • In kitchen areas that have accumulated grease.
  • In bathroom areas that have soap scum. Or in bathrooms that get a lot of misted sprays, such as hairspray.
  • In areas that receive a lot of skin contact (near door handles; door jambs; etc.)
  • In rooms with unusual amounts of nonwater-soluble markings (for instance, Crayons in a kid's room).
  • On the walls, above heating registers.