Trisodium phosphate, better known as TSP, is a heavy-duty cleaner that has prepped walls for paint and stripped grime for decades. It comes as an inexpensive, odorless dry powder that dissolves in hot water into a mostly clear, slightly cloudy solution, and a $5 to $10 box handles dozens of cleaning jobs around the house. TSP is sold in most hardware stores and home centers, usually near the paint prep supplies. TSP belongs to a larger phosphate family; in building materials, magnesium phosphate cement offers a different set of characteristics and advantages for repair work, while TSP stays focused on surface cleaning.
What Trisodium Phosphate Is
The packaged product labeled TSP is a blend of 75 to 80 percent trisodium phosphate and 20 to 25 percent sodium carbonate. Mixed with hot water, it cuts through dirt, grease, and mold in places a general cleaner cannot reach, such as the film on kitchen cabinets or the soot above a fireplace. It is not a disinfectant and does not kill mold spores; it removes the surface growth so a follow-up treatment can finish the job.
How the Blend Works
Trisodium phosphate raises the pH of the wash water, which breaks down fatty soils and loosens stubborn residues. The sodium carbonate portion softens water and buffers the solution so it keeps working as it picks up grime. The two ingredients together make TSP faster on grease than most all-purpose sprays.
A Project-Level Snapshot
Typical TSP tasks fit into an afternoon. A single wall takes about 15 minutes of active work and 20 to 30 minutes total, and the skill level suits beginners. TSP is sold as powder that must be mixed fresh, and as a liquid concentrate in some regions; the powder form stores longest and costs least per gallon of solution.
The store product is a formulated cleaner, not raw trisodium phosphate. Straight TSP powder without the carbonate buffer is harsher and harder to rinse. Knowing what is in the box explains why two brands can behave differently at the same dilution.
How TSP Cleans and Where It Works Best
TSP excels at three jobs: degreasing, de-sooting, and preparing surfaces for paint. Paint will not adhere well over greasy or chalky walls, so a TSP wash is a standard step before repainting kitchens, bathrooms, and trim. Detailed guidance on cleaning with TSP covers dilution, dwell time, and rinsing for each surface type.
Surfaces That Respond Well
Painted walls and cabinets, fireplace surrounds, baseboards, and exterior siding headed for repaint are the classic TSP targets. It also removes mold and mildew stains from hard surfaces such as tile, concrete, and masonry, and it cuts the soap scum that builds up around sinks and tubs.
TSP also levels the playing field before other projects. It removes the chalky oxidation on old siding, strips the film left on painted trim, and gives adhesive and caulk a clean base. For exterior work, wash on a cloudy day so the solution does not dry before rinsing.
Why Paint Prep Demands It
Latex and oil paints both need a clean, dull surface to bond. TSP removes the invisible film of cooking grease and household soil that makes paint peel, and its mild etching action gives the new coat something to grip. Skipping this step is a leading cause of paint failure in kitchens and bathrooms.
How to Mix and Apply TSP
Mixing TSP is straightforward, but the solution is caustic, so preparation matters. Work in a ventilated area, wear rubber gloves and eye protection, and cover skin from splashes. Follow the label ratio, typically 1/2 cup of powder per 2 gallons of hot water for general cleaning, and stir until the powder is fully dissolved. Hot water activates the powder faster than cold, but boiling water makes the solution dangerously hot to handle.
Tools You Need
- Rubber gloves and safety glasses
- Sponge or stiff scrub brush
- Bucket for hot water
- Clean rinse water and a second sponge
- Drop cloths to protect floors and furniture
- Mix the powder into hot water and stir until dissolved.
- Wet a sponge or brush in the solution and wash from the bottom of the surface upward.
- Let the solution sit for 30 to 60 seconds on heavy grime, then scrub.
- Rinse thoroughly with clean water, changing the rinse water often.
- Let the surface dry completely before priming or painting.
Work one section at a time so the solution never dries on the surface. Dried TSP residue is harder to rinse off than fresh solution and can leave a white haze on dark paint. A second person with a rinse sponge keeps the pace steady on large walls.
Rinsing Rules
Residue left on the wall can make new paint fail just like the old dirt did. Rinse every section with fresh water, and use a hose for exterior work. Test a small hidden area first on painted, glazed, or colored surfaces, because TSP can dull some finishes.
What to Clean With TSP and What to Avoid
TSP is powerful, and power needs boundaries. The table below summarizes where it helps and where it causes damage.
| Surface | Safe to clean | Notes |
|---|---|---|
| Painted walls before repaint | Yes | Rinse thoroughly after washing |
| Kitchen cabinets | Yes | Removes the grease film |
| Fireplace surrounds | Yes | Heavy scrubbing on soot |
| Aluminum and soft metals | No | Can discolor or corrode |
| Unsealed wood | No | Raises the grain and darkens |
| Glass and mirrors | With care | Streaks unless rinsed well |
| Skin and eyes | No | Caustic; wear protection |
Reading the Label
Brands blend TSP differently, and some add surfactants that change the dilution instructions. Always follow the ratio on the container, and test an inconspicuous spot before tackling the whole surface. If the label warns against a material, trust the warning.
Surfaces That Resist TSP
Soft metals, unsealed wood, and waxed floors react badly to the alkaline solution. TSP can also dull anodized aluminum and leave a cloudy film on glass if rinsing is rushed. When in doubt, wash a sample area first and inspect it once dry.
TSP belongs in the maintenance rotation, not the daily cleaning drawer. Reserve it for seasonal deep cleans, paint prep, and the grime that general-purpose cleaners cannot shift. Regular household cleaners handle weekly dusting and touch-ups, which keeps TSP use occasional and exposure low.
Safety and Environmental Considerations
Phosphates feed algae when they reach lakes and rivers, which is why many communities restrict phosphate detergents and why some areas ban TSP outright. The product remains legal in many places, but responsible use means keeping wash water out of storm drains and choosing alternatives where local rules require.
Why Some Areas Ban It
Municipal bans target phosphate loading in wastewater. Check local regulations before buying TSP, and note that many hardware stores in restricted areas stock only phosphate-free cleaners. Online retailers still ship TSP to most regions, which makes the local rule the real deciding factor.
Handling Precautions
- Wear gloves, eye protection, and long sleeves.
- Keep the powder and mixed solution away from children and pets.
- Never mix TSP with bleach or ammonia-based cleaners.
- Dispose of wash water down the sanitary drain, not the street gutter.
Storing the Powder
Keep the box tightly sealed in a dry, cool spot. The powder absorbs moisture from the air, and clumped TSP is harder to measure and dissolve. A sealed container with the original label lasts years without losing strength.
Wash water from interior TSP jobs can go down the sanitary drain, where treatment plants handle the phosphate load. Exterior wash water should be directed onto soil or landscape areas rather than pavement, so it filters before reaching waterways.
Phosphate-Free Alternatives and Substitutes
Several cleaners deliver similar degreasing power without phosphates. A practical comparison of trisodium phosphate substitutes helps you match the alternative to the job: washing soda for general degreasing, oxygen bleach for stains and mildew, vinegar for light cleaning, and commercial TSP-free preparations for paint prep.
Household Standbys
Washing soda, sold as sodium carbonate, is the closest single-ingredient match because it is already part of the TSP blend. Baking soda adds mild abrasion for scrubbing, and oxygen bleach handles organic stains that plain alkali leaves behind. Vinegar works on light soap scum but should not be mixed with bleach.
Commercial TSP-Free Cleaners
Products labeled TSP substitute or TSP-PFree blend sodium carbonate, sodium metasilicate, and surfactants to mimic TSP behavior. They work well for paint prep, though some leave a film that still requires a full rinse. Compare the active ingredients on the label and test on a hidden area before a full job.
Some brands label a product TSP when it is actually phosphate-free, so check the ingredient list rather than the front of the box. Dilution matters with substitutes too; washing soda is strong enough to irritate skin at the same ratios as TSP, so the same gloves and rinsing rules apply.