Use muriatic acid to clean concrete only when no other cleaner will do the job. Muriatic acid, also called hydrochloric acid, is the most dangerous chemical product sold on the open market. Phosphoric acid can be used as a safer alternative for cleaning concrete. Yet if the concrete stain contains minerals phosphoric acid does not remove, muriatic acid can be used safely outdoors while the wind is low. Protective gear and clothing are required. A neutralising agent and running water must also be at hand. Use muriatic acid to clean concrete or prepare concrete surfaces for paint or sealer.
- Skill level:
Things you need
- Acid resistant gloves
- Rubber boots
- Splash guard goggles or a face shield
- Respirator with acid--grade filter
- Vinyl coated overalls
- 5 gallon plastic bucket
- 2 gallon bucket (plastic, metal or wooden)
- Long-handle scrub brush
- 2 large boxes baking soda
- Hose and sprayer with running water supply
Put on acid resistant gloves, splash guard goggles or face shield, respirator, vinyl coveralls and rubber boots. Guard against severe skin burns and irreversible eye damage muriatic acid can cause on contact.
Moisten the concrete to be cleaned. Spray water to soak all grass and plants within 20 feet of the area of the concrete to be cleaned. Brushing creates tiny splatter that can be carried by a light breeze.
Pour one gallon of water into a 5-gallon plastic bucket. Add 354ml, 1 1/2 cups, of muriatic acid to the water. The ratio is 10 parts water to 1 part acid. Be sure to put the water in the bucket before adding the acid. Stir the acid water mixture with the long--handle scrub brush.
Scrub the wall, sidewalk or patio with the acid mix the scrub brush holds. Do not pour acid mix on the concrete surface. Leave on for no more than 10 minutes.
Rinse the area with running water. Brush away any loose residue and rinse again.
Neutralise the area. Pour one gallon of water into a 2 gallon bucket and add 236ml, one cup, of ammonia. Spray or brush the ammonia mix liberally over the cleaned surface and immediate surroundings. Rinse thoroughly with water again.
Neutralise the remaining acid mix. Add another gallon of water to the 5-gallon plastic bucket of acid mix. Pour in baking soda while slowly adding another gallon of water. Continue to add baking soda and water until the fizzing stops. The neutralised mixture can be disposed of in a sink or storm drain.
Tips and warnings
- Try cleaning with phosphoric acid first. Follow label dilution instructions and see if you can get satisfactory results without using the more dangerous muriatic acid.
- If a spill occurs while cleaning with muriatic acid, neutralise the grounds with an ammonia and water mixture quickly. Then rinse thoroughly.
- Safe handling of muriatic acid is crucial to the safety of humans, pets, foliage and metals. Muriatic acid will eat anything except certain plastics. Keep unused muriatic acid closed in the plastic container in which it was sold.
- Keep protective gear and clothing on until all cleaning and neutralising is finished.
- Never use muriatic acid indoors. Acid vapours burn the linings of the nose, throat and lungs.
- Never use muriatic acid for cleaning on a breezy or windy day
- Never pour water into muriatic acid. Always put water into the mixing container first, then add the acid. Pouring water on muriatic acid causes it to quickly release heat in an eruption that can cause the acid to splash out of the bucket.
- Never pour muriatic acid down a sink or storm drain unless it has been completely neutralised.
- Never allow muriatic acid to contact skin or eyes. If it does, flush with water and get medical attention immediately.