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Do You Really Need to Wash Interior Walls Before Painting?

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Question: Do You Really Need to Clean Interior Walls Before Painting?

I don't mind painting, but I hate cleaning. I keep reading that, before painting my interior walls, I should clean them. Do I really need to do this? Is there any way around this requirement?

Answer: Paint manufacturers recommend that you clean interior walls with trisodium phosphate (TSP), a cheap powder that you mix with water. But do you really need to do this?

I'm going out on a limb here and say that in most cases--if you have a normal house, normal rooms--you do not need to scrub with TSP when preparing to paint.

Lightly washing with TSP is always preferable to not lightly washing with TSP. Simply put, cleaner is always better. But if a full wash-down is preventing you from tackling the painting, then I believe it's possible to skip the wash, in most cases.

How 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. Besides, what does perfectly clean entail? If you clean interior walls with TSP but aren't able to paint for two weeks, I guarantee that your walls have already begun to accumulate dust; it happens that fast.

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

I emphasize that 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.

Read Interior Painting Tips From Martha Stewart Living's Kevin Sharkey

Interior Painting Prep, Minus the TSP

If you're going to skip the 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.

Washing Alternative:  Pole Sanding

Professional painters hate washing walls.  There are many good reasons for this.  For one, they're not in the business of washing--they're in the business of painting.  For another, 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 him 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 definitely keep TSP on hand as an addition to your collection of essential painting supplies. I 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 non water-soluble markings (for instance, Crayons in a kid's room).
  • On walls, above heating registers.
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