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Glossary

Trisodium Phosphate

Trisodium Phosphate

This is a strong chemical powder you mix with water to clean stubborn dirt, grease, and old paint off your house. You often use it to wash your siding or prep your walls before you apply a new coat of paint. It is very powerful, so you must wear gloves and protect your plants when you spray it.

Reviewed by Hank AshUpdated July 3, 20263 min read

Origin

The name describes its chemical makeup of three sodium atoms bonded to a phosphate group. Chemical companies introduced it as a heavy duty cleaning agent in the 1930s before modern liquid detergents took over.

How you'll see it used

  • Your painting contractor's estimate includes a line item for washing the kitchen walls with trisodium phosphate to remove heavy cooking grease before applying primer.
  • While buying supplies to pressure wash your dirty vinyl siding, the hardware store clerk recommends picking up a box of TSP to mix into your pump sprayer.
  • You read the instructions on a bucket of heavy duty concrete patch, and it tells you to scrub the old driveway crack with trisodium phosphate so the new cement bonds properly.

What is trisodium phosphate?

Trisodium phosphate is a strong chemical cleaning powder. People usually just call it TSP. You buy it in a cardboard box or plastic tub at the hardware store and mix it with warm water. It isn't like the gentle soap you use to wash dishes or clothes. It's a heavy duty cleaner that strips away stubborn dirt, thick grease, soot, and old smoke stains. Chemical companies introduced it in the 1930s before modern liquid detergents existed. The name simply describes its chemical makeup of three sodium atoms bonded to a phosphate group. Today, you mostly use it when you need a perfectly clean surface before you start a big home improvement project. It leaves no soapy residue behind, which makes it perfect for prep work.

When to use it around your house

You'll run into this cleaner most often when you tackle painting or exterior cleaning jobs. If you paint over a dirty or greasy wall, the new paint will bubble and peel right off. Washing the wall with this mixed powder removes all the invisible oils and grime. It also slightly dulls shiny old paint so your fresh coat sticks much better. This step is very important when you update your Interior: Paint, Drywall & Trim.

You might also use it outside your house. It does a great job cleaning mold, mildew, and dirt off wood fences, brick masonry, and vinyl siding. If you're washing your Exterior: Siding, Garage & Decks, a weak mix of this powder and water can make old surfaces look brand new. You just apply it with a large sponge or a stiff brush, let it sit for a few minutes, and then rinse it away with a hose.

How much does it cost?

You don't need to spend a lot of money to get professional cleaning results. This powder is very cheap compared to specialty liquid cleaners. A standard one pound box usually costs 5 to 10 dollars. A larger four pound box or bucket costs 15 to 25 dollars. Prices and ranges vary depending on your local hardware store and the brand you buy. One small box goes a very long way. You only need to mix a half cup of the powder into two gallons of warm water for most basic cleaning jobs. A single box will easily clean all the walls in a large living room or kitchen.

How to stay safe when you use it

This cleaner is incredibly powerful and highly alkaline. It will burn your bare skin and severely irritate your eyes if you aren't careful. You must take basic safety steps before you even open the box.

  • Wear thick rubber gloves to protect your hands and wrists.
  • Put on safety goggles so accidental splashes don't get in your eyes.
  • Wear long pants and a long sleeve shirt to protect your skin.
  • Open your windows and doors to keep fresh air moving through the room while you clean indoors.
Protect your yard: If you use this cleaner outside, soak your plants with plain water first. Then cover them with plastic tarps. The strong chemicals will easily burn or kill your grass and landscaping if the dirty runoff touches them.

The rise of substitute cleaners

You might notice boxes labeled as a substitute cleaner sitting right next to the real thing at the store. Real trisodium phosphate contains a lot of phosphorus. When this chemical washes down your driveway and flows into storm drains, it eventually reaches local lakes and rivers. The extra phosphorus causes massive algae blooms that ruin the water and kill fish. Because of this environmental impact, many states and counties strictly ban the real chemical for outdoor use. If you live in one of these areas, stores will only sell the substitute version. The substitute is much safer for the environment, doesn't require as much rinsing, and works almost as well for basic painting prep jobs.

Frequently asked

Do I have to rinse the walls after I clean them with this powder?

Yes, you must rinse the walls thoroughly with a clean, damp sponge. If you leave the chemical residue on the drywall, your new paint will not stick properly. It takes extra time, but rinsing guarantees a smooth and lasting paint job.

Can I use trisodium phosphate to wash my wood deck?

You can use it to clean an old wood deck, but it will strip away old stains and sealers. It also darkens bare wood, so you will likely need to apply a wood brightener afterward. If you just want to remove mild dirt, a gentle deck soap is a safer choice.

Is the substitute version just as good as the real thing?

The substitute works perfectly fine for scrubbing dirty walls inside your house before you paint. However, it doesn't cut through heavy outdoor grease and deep soot quite as well as the original chemical. Many homeowners prefer the substitute anyway because it is much safer for their plants and local waterways.

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