Acid Cleaning Concrete with Muriatic Acid

Acid cleaning concrete with muriatic acid should only be a last resort.

What is muriatic acid?

Muriatic acid is an industrial strength solution of hydrochoric acid. It is highly corrosive and extremely dangerous and will damage just about anything it touches. The fumes can burn your nose, throat, and even your lungs. It's commonly used as a cleaning agent for concrete and masonry surfaces but shouldn't be used without proper preparation and precaution.

How does it clean concrete?

Muriatic acid reacts with cementitious material and produces a powder residue called calcium carbonate. When the residue is removed, it leaves behind a porous and roughened surface. This process is called acid etching. Etching aids in the bonding of concrete coatings to the surface but not desirable for basic cleaning because the opened pores make the concrete more susceptible to damage.

Precautions for using muriatic acid

Read all instructions on the label. You must use proper preparation and extreme caution. Wear long pants, sleeves, rubber gloves, and eye protection.
Keep a source of water nearby such as a garden hose and a neutralizing agent such as baking soda for accidental spills and splashes.
Cover nearby objects with plastic to protect from overspray.
Don't spray outside on a windy day.
Make sure there's adequate ventilation. Not only are the fumes harmful to people, but are also harmful to other materials, especially metals, and can cause long term damage. Because of this, acid cleaning with muriatic acid indoors is not recommended.

How to use muriatic acid

Muriatic acid should be diluted to at least 1 part acid to 10 parts water. Mix the acid and water in a plastic container. Always pour acid into water, never water into acid. Mixing the two causes a reaction that gives off heat. This reaction is much more sudden and violent when water is poured into acid as opposed to vice versa.

The diluted acid can be applied with a brush or sprayer depending on the circumstances. If you're going to spray, it's best to buy a cheap sprayer and throw it away when finished.

Before acid cleaning with muriatic acid, consider some of the safer alternatives.

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Acid Cleaning Concrete with Muriatic Acid