How to Clean Walls Before Painting

wiping walls down with a sponge

​The Spruce / Ruthie Darling

No DIY advice is ignored as often as the recommendation to thoroughly wash the walls before priming and painting. Even careful DIYers are tempted to bypass this step when the walls appear to be clean and in good shape, and many do-it-yourselfers don't bother to clean in any way, instead opting to simply slather paint over the walls. And the immediate consequences of skipping the cleaning step aren't always evident. In some cases, the paint job may hold up fine for many years, leading you to wonder why nearly all paint manufacturers firmly insist that washing the walls is a critical part of painting prep.

Further adding to the confusion is the fact that paint manufacturers themselves don't agree on just what kind of cleaning is essential.

Recommendations of Major Manufacturers

The major paint manufacturers have different recommendations on the necessity of painting interior walls before painting, ranging from a cursory wiping to firm scrubbing with mild chemicals. Consider the advice of the major paint companies:

  • PPG: "Wipe walls clean of dust and dirt."
  • Behr: "If you need to remove any oil, grease or wax stains, apply a mild detergent with a sponge onto a lightly water-dampened surface, rinse with clean water and allow it to dry."
  • Benjamin Moore: "Most walls can be washed using a sponge and warm water. For surfaces that have exposure to oil or grime, like kitchen walls, wash with a solution of water and grease-cutting detergent and follow up with clean water to remove any residual cleaning agent. Finish by wiping the walls with a damp cloth."
  • Sherman Williams: "Washing your walls and trim will remove grime, cobwebs, dust and stains that can prevent your paint from adhering. Use a mixture of lukewarm water and mild soap, gently rubbing in a circular motion. Rinse your walls using a slightly damp cellulose sponge.
  • Valspar: " Use an ordinary sponge mop to clean your ceiling and walls thoroughly with TSP and water. Rinse well and let dry. Moving from top to bottom, clean walls and moldings with sponges or rags."

The reality, though, is that many people skip this step, or clean in a more cursory way. Not even pro painters are diligent about cleaning walls before they paint.

Professional Painters Usually Don't Wash Walls

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. Washing cuts into painting time, which cuts into their income, so don't expect your hired painter to wash down your walls unless you agree to pay them more for the service. Better yet, hire a cleaner to do this work, or do the cleaning yourself before the painter arrives.

Instead, your hired painter is likely to pole-sand the flat surfaces with fine-grit sandpaper. Light sanding sloughs off sticky dirt and junk, deglosses surfaces, and knocks down some of the stipple.

When You Might Be Able to Skip Washing

If you are painting the walls yourself and want to omit the step of washing walls as part of the preparation, the surfaces should meet at least most of the following conditions:

  • No excessive dust present
  • No crayon or grease stains present on the walls
  • No wood-burning fireplace in the house
  • Walls have little or no contact with hands
  • No pets in the house
  • No cooking or bathing takes place in the room (meaning kitchens and bathrooms should always be washed before painting).
  • Vertical surfaces only (trim work and ledges should always be washed)

The spaces that might qualify as rooms that don't require active washing with detergent or TSP include:

  • Living room that does not get a lot of activity and was painted recently
  • Master bedroom used by adults, not children
  • Dining room dedicated to dining only, rather than cooking
  • An office
  • A family room that is well-treated with no wood-burning fireplace
  • Powder room used only for toilet activities and hand-washing

Even these rooms, no matter how pristine, will require a wipe-down to eliminate loose dust.

When to Wash With Soap and Water

As noted above, most paint manufacturers recommend that you clean walls with at least mild detergent and water before painting. Although modern paints are so good that they bond well to almost any surface, it will adhere best to surfaces that are perfectly clean and smooth.

How to Wash Walls With Soap and Water

Walls that are visibly dusty or dirty from handprints or other grime should be washed with detergent and water. A good cleaning routine for walls looks like this:

  1. Remove the Big Stuff

    Knock down the dust bunnies and cobwebs with a broom.

  2. Clean 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.

    wiping walls and baseboards with a cloth
    The Spruce / Ruthie Darling
  3. Vacuum

    With the bristle attachment on a home or shop vacuum, vacuum any floor areas near the walls.

    using the vacuum brush attachment on a baseboard
    The Spruce / Ruthie Darling
  4. Wipe

    Mix in a mild detergent with a bucket of warm water, and wipe down all the surfaces you will paint using a damp (not sopping) sponge.

    sponge in soapy water
    ​The Spruce / Ruthie Darling
  5. Rinse

    Immediately after washing, rinse the walls with clear water and a damp sponge.

    washing walls with a damp sponge
    ​The Spruce / Ruthie Darling

When to Scrub with TSP

TSP (trisodium phosphate) is an inorganic powder (chemical formula Na3PO4) that creates an alkaline cleaning solution when mixed with water. The alkalinity makes it excellent at dissolving greases and oils, and TSP is recommended as a cleaning solution under certain conditions:

  • 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

TSP also lightly etches surfaces, which makes it good for slightly dulling high-gloss paint surfaces. If the previous paint is a glossy finish, TSP washing can take the place of sanding to help the new paint bond.

When washing with TSP, mix the powder with water as directed by the product label, then wash the walls with a sponge dampened in the solution. Work in sections about 3 feet square. Let the solution sit for about two minutes on each section, then scrub again with TSP. Immediately rinse each section with another sponge dampened in clear water.

TSP can sometimes stain wood floors, so protect them with drop cloths. Also, keep the TSP off any surfaces that won't be painted. It is mildly caustic and may etch painted or stained woodwork. Wearing rubber gloves is recommended.