How to Clean Walls Before Painting (No TSP Required)

You’ve picked the color, bought the rollers and blocked off a weekend. Then an old how-to tells you to scrub every wall with TSP (trisodium phosphate) first. The good news: learning how to clean walls before painting is mostly about matching the cleaner to the dirt, and most walls need far less muscle than you’d think.

Cleaning walls before painting gives new paint something solid to grip. Dust, grease and soap film get in the way, and the trouble they cause (peeling or tiny craters in the finish) is much harder to fix once the paint is on.

Below, we’ll cover why prep matters, how to size up each room, a simple 10-step method, what TSP really is and the gentler options we reach for instead. As we like to say, you don’t have to clean with a jackhammer.

Should You Clean Walls Before Painting? Yes, and Here’s Why

Yes, every time. Walls look clean from across the room, but up close they hold dust, skin oils around switches and door frames, cooking grease and bathroom soap film. That’s why Sherwin-Williams’ prep steps for previously painted walls start with washing away dirt, grease, soap and oil, then rinsing well. Skipping prep invites two problems:

• Fisheyes and craters. Sherwin-Williams describes fisheyes as small, crater-like openings that appear during or shortly after painting, and it generally traces them to surfaces contaminated with oil, wax, silicone or grease. That makes the kitchen the room to watch.

• Poor adhesion and peeling. Paint needs a clean surface with a little texture to grab. Sherwin-Williams warns that any coating applied to a hard, slick, glossy surface is likely to peel.

Size Up Each Room Before You Start

Walk each room with a flashlight held close to the wall. Light skimming across the surface shows grime, drips and shiny patches you’d otherwise miss. Most rooms fall into one of these groups:

• Bedrooms, living rooms and hallways. Usually just dust, cobwebs and fingerprints around switches, doorknobs and stair rails. A dusting and a mild soap wash will do.

• Kitchens. Run a fingertip over the wall near the stove. If it feels tacky or leaves a smear, there’s a grease film, the kind of contamination behind fisheyes. Plan on a degreaser.

• Bathrooms. Dark speckles in corners, above the shower or around the window often mean mildew. It needs its own treatment, plus a fix for the moisture that feeds it, before any paint goes on.

• Homes with smokers. A yellow or brown tint and a slightly sticky feel point to smoke residue. Expect a degreaser wash (sometimes two), a thorough rinse and a stain-blocking primer.

• Trim, doors and cabinets. If the paint looks shiny or feels slick, it needs deglossing so the new coat can grip.

Safety first: If your home was built before 1978, it may have lead-based paint, and sanding or scraping it (steps 8 and 9) can create dangerous lead dust. The EPA recommends having a certified lead inspector or risk assessor test the surfaces first, and if you can’t confirm your home’s age, assuming lead is present. Its lead-safe practices, meant to protect family members and especially children, include sealing off the work area, wearing a disposable N-100 respirator, misting surfaces before sanding or scraping, fitting power tools with HEPA vacuum attachments and cleaning up with wet disposable cloths. For renovation, repair and painting projects in pre-1978 homes, the EPA recommends hiring a lead-safe certified contractor.

How to Clean Walls Before Painting in 10 Steps

Work one wall at a time, wear gloves for every wet step and spot test each cleaner in a hidden area, such as behind a door, before you start.

1. Clear and protect the room. Move furniture to the center, lay drop cloths or old towels along the baseboards and tape over outlets and switches to keep splashes out.

2. Dust and vacuum. Wipe each wall from ceiling to floor with a dry microfiber cloth or duster, then vacuum the baseboards and floor edges. Removing loose dust first keeps it from turning into muddy streaks when you wash.

3. Wash with a gentle cleaner. For most rooms, about a teaspoon of mild dish soap in a gallon of warm water is plenty. Wring your sponge until it’s barely damp, wash about three feet at a time and catch drips before they run. Change the water when it turns cloudy.

4. Degrease the kitchen. Around the stove, range hood and backsplash, switch to a grease-cutting cleaner such as a kitchen degreaser. Follow the label and ventilate with an open window or the range fan. Work in small sections so the film lifts instead of smearing.

5. Treat mildew and let it dry. For small patches, the EPA advises scrubbing mold off hard surfaces with detergent and water, then drying completely; wear goggles and gloves. We skip bleach for this job (here’s why). If you do use it, ventilate well and never mix it with any other cleaner; the EPA specifically warns that bleach mixed with cleaners that contain ammonia can produce toxic fumes. Fix the moisture source too, and see the EPA’s guidance for patches over about 10 square feet.

6. Rinse if your cleaner calls for it. Always rinse after a soap wash; for other products, follow the label. Use a second sponge and clean water to lift leftover cleaner, and change the rinse water often so you aren’t spreading soap back on.

7. Let walls dry completely. Benjamin Moore says the most important part of washing is letting everything dry thoroughly, since primer or paint applied to damp walls can blister. Follow any wait time on your cleaner’s label and open a window or run a fan. Before moving on, touch-test corners and the bottom of each wall, where water collects.

8. Patch and sand. Scrape off any loose or flaking paint, fill nail holes and dings with spackling compound, let it dry and sand it smooth. Wipe away the dust with a damp cloth and let that dry too.

9. Degloss glossy surfaces. On shiny trim, doors, cabinets or glossy walls, Sherwin-Williams recommends sanding the gloss dull, then using a bonding primer if the surface still feels slick. On sound paint, a liquid deglosser can be a no-sanding alternative. Wear a dust mask for sanding, and gloves plus fresh air for deglossers. In a pre-1978 home, test for lead before you sand and follow the lead-safe practices in the safety note above.

10. Prime stains and patches. Sherwin-Williams advises sealing water, smoke, ink, pencil and grease stains with a stain-blocking primer and priming bare areas, such as fresh patches, before the topcoat. Once the primer is dry, you’re ready to paint.

TSP Explained: Should You Use Trisodium Phosphate to Clean Walls?

Classic TSP wall cleaner is made with trisodium phosphate, a white crystalline compound that dissolves into a strongly alkaline solution. PubChem’s chemical record lists a pH of about 12 for a 1% solution and notes TSP’s ability to break fats and greases down into water-soluble glycerin and soap.

That strength comes with hazards. The hazard classifications compiled in PubChem list TSP as a skin irritant and a serious eye irritant that may also irritate the airways, and some agencies rate it more severely, as able to cause serious eye damage and skin burns. If you do use it, gloves and eye protection are a must.

Then there’s the phosphate. The EPA explains that too much nitrogen and phosphorus in water makes algae grow faster than ecosystems can handle, and the resulting blooms can cut oxygen enough to sicken or kill fish. Its advice for households is to pick phosphate-free soaps, detergents and household cleaners.

Phosphorus in cleaners can be a legal issue, too. In our home state of Illinois, the Regulation of Phosphorus in Detergents Act has barred using, selling or making cleaning agents with more than 0.5% phosphorus by weight since July 1, 2010, with exemptions for certain agricultural, commercial and institutional uses. Its definition of a cleaning agent covers household cleaners and degreasing compounds. Rules vary, so check your own state’s before buying a phosphate cleaner.

We’ve been making cleaners since 1997, and our take is simple: for most homes, using trisodium phosphate to clean walls is more chemistry than the job needs. Gentler cleaners handle everyday grime, and the tough jobs have phosphate-free options.

What to Clean Walls With Before Painting: TSP Substitutes and Other Options

The best wall cleaner before painting is the mildest one that gets the job done. Here’s how the common choices compare:

• Mild dish soap and warm water. Best for bedrooms, living rooms and hallways. Benjamin Moore notes that most walls can be washed with a sponge and warm water, with a grease-cutting detergent for oily kitchen walls and a clean-water rinse after. Trade-off: it’s slow on heavy grease and needs that rinse.

• Degreasers. Best for kitchens and homes with smokers, where an oily film is the main problem. Trade-off: stronger formulas call for more care, so read the label, spot test and ventilate.

• Carbonate-based TSP substitutes. Best for heavy grime when you want to skip phosphates. Know what you’re buying, though: formulas vary, and the safety data sheet for one phosphate-free TSP substitute lists sodium sesquicarbonate as 90 to 95% of the powder, a pH of 10 to 11 (1% solution) and an eye and skin irritant warning. Phosphate-free isn’t the same as gentle, so gloves and eye protection still apply.

• Liquid deglossers. Best for glossy trim, doors and cabinets. A deglosser chemically dulls a shiny finish so new paint can grip without sanding. Trade-off: deglossers don’t smooth patches or rough spots, so you’ll still sand those. Follow the label, ventilate and wear gloves.

Prepping glossy trim, doors or cabinets? Our 5 Minute Paint Prep cleans, degreases and deglosses in one step, with no sanding. It’s free of acids and bleach and is designed to work with our CleanWalls tool. For mildewed bathroom walls, stick with the detergent-and-water approach in step 5 and fix the moisture first.

Keep Walls Paint-Ready Between Projects

The easiest prep job starts with walls that are already fairly clean. Dusting a couple of times a year and wiping switches, door frames and kitchen walls more often keeps grease and grime from building into a film you’ll have to scrub off next time. Once your new paint has cured (check the can for timing), our guide to cleaning painted walls without damaging them covers a gentle routine that protects the finish.

Make Wall Cleaning a 5-Minute Habit

Our company motto is simple: when you know the right thing, do the right thing. Now you know how to prep your walls for paint without reaching for TSP. We also know the real reason walls get skipped: hauling out a ladder, a bucket and a sponge turns a quick job into a weekend project. That’s why we created the 5-Minute Clean Walls Bundle.

It pairs our non-toxic CleanWalls spray with a wall cleaning mop built for the job: a telescoping pole that reaches from baseboards to ceilings, a 360-degree swivel head for corners and trim, and two machine-washable microfiber mitts you can reuse again and again. The spray is safe on painted walls and comes in several scents, including unscented. No ladders, no kneeling and no harsh fumes.

It’s backed by our 60-day money-back guarantee, so you can put it to work in every room and decide for yourself.

Shop the 5-Minute Clean Walls Bundle

Frequently Asked Questions

Do you need to wash walls before painting if they look clean?

Yes. Walls that look clean still collect dust and skin oils, especially around switches, door frames and stair rails. In a bedroom with no grease or stains, a thorough dusting plus a mild soap wash of those high-touch spots may be enough. Kitchens, bathrooms and homes with smokers deserve a full wash, rinse and dry every time.

Can you paint over mildew?

No. The EPA says not to paint or caulk moldy surfaces and notes that paint applied over mold is likely to peel. Scrub small patches with detergent and water and fix the moisture source, such as a leak or a weak bathroom fan. Let the area dry completely before you prime and paint.

Do you need to sand if you use a liquid deglosser?

Often not. On sound, shiny paint, a liquid deglosser can stand in for scuff-sanding if you follow the product’s directions for application and drying time, and if the surface still feels slick afterward, sand it dull or use a bonding primer. You’ll still need to sand patched spots, rough areas and the edges of any chipped paint. In homes built before 1978, have the paint tested for lead before sanding or scraping anything.

Do you need to prime walls after washing them?

Not always. Primer earns its place on fresh patches, stains, porous walls and slick finishes. Benjamin Moore recommends primer especially when walls are porous or have stains that need covering. If your walls are sound, clean and close to the new color, check your paint can’s directions to see whether a separate primer is needed.