What Is The pH Of Brick Acid?

by Jessica Clifton

The pH of brick acid varies depending on factors, such as temperature and concentration. Commercially available brick acid typically has a pH range of between 0 and 2. However, highly concentrated brick acid of more than 36% by mass can have a negative pH (below 0). 

As the name suggests, brick acid is normally used to remove stains and mineral deposits from bricks and other types of masonry. Continue reading to learn more about the pH of brick acid and how it compares to other acids.

Introduction to pH: what is pH?

The acidity or basicity of a substance is usually measured in terms of pH level. It’s typically depicted as a 14-step scale from 0 to 14, with 7 being neutral. 

The pH scaleDevised by Danish chemist Søren Sørensen, the pH scale is a logarithmic scale of base 10 that measures a solution’s potential to accept protons in the form of hydrogen ions. For example, a substance that has a pH level of 8 is ten times more alkaline than a solution with a neutral pH of 7.

The pH scale is closely associated with the self-ionisation of water. Under standard conditions, pure water spontaneously dissociates into hydronium ions and hydroxide ions:

H2O + H2O ⇌ H3O+ + OH

The concentrations of the ions are almost exactly 1.00×10−7 mol dm−3 at 25 °C and 0.1 MPa. When an acid or a base substance is dissolved in water, the ions will dissociate into either hydroxide or hydrogen ions, plus their acid or base conjugates.

The pH or potential of hydrogen is a measure of how acidic or basic (alkaline) a solution is. It’s equal to the common logarithmic value of the reciprocal concentration of hydrogen ions expressed in mol dm−3 of aqueous solution. Although the scale is commonly depicted as having a range of between zero and 14, the pH of a substance can actually be negative (strongly acidic) or above 14 (strongly basic).

Brick acid basics

Brick acid is basically an aqueous solution of hydrochloric acid. A corrosive and hazardous liquid, it’s used to remove tough stains and mineral deposits from bricks. Brick acid works by dissolving calcium carbonate (a common source of efflorescing salts in bricks) through a neutralisation reaction between the hydrochloric acid and the alkaline mortar. 

As the equation below shows, the chemical reaction produces calcium chloride, carbon dioxide, and water:

CaCO3 + 2HCl → CaCl2 + CO2 + H2O

Brick acid can also be used to clean concrete floors, effectively removing splashes of cement, limescale, grease, and other dirt particles from the surface. However, it shouldn’t be used on natural materials like limestone or marble because it can damage the natural beauty of the stone

Composition of brick acid

As an aqueous solution of hydrochloric acid, brick acid is composed of water and hydrogen chloride. Chemically, the hydrogen chloride becomes hydrochloric acid when its ions completely dissociate in water.

Muriatic acid – a less pure hydrogen chloride solution – can also be used in brick acid, but it may not work as well. However, it’s cheaper to manufacture and sells at a comparatively lower price than laboratory-grade hydrochloric acid.

Common uses

Brick acid is used to clean a variety of brickwork and masonry. It’s often applied immediately after construction to remove unsightly mortar mess and give the brickwork a more uniform appearance. The chemical is also used to clean and maintain existing buildings, as well as pavements and concrete floors.

Brick acid’s ability to dissolve cement residue and calcium deposits makes it particularly useful in the building industry and commercial cleaning trade. You can read more about the uses of brick acid here.

The pH of brick acid

The acidity level or pH of brick acid varies depending on factors, such as concentration, temperature, and the presence of impurities. The typical pH range of most commercially available brick acid is between 0 and 2. 

The most effective concentration of brick acid is 36% by mass. At this concentration, it can dissolve calcium deposits and remove surface dirt without weakening the structure of the brick.

Graffiti on a wall outside a cafe
Brick acid is used to clean graffiti off walls

pH of brick acid vs. other common acids

So how does the pH of brick acid compare to that of other common acids? Vinegar – a diluted acetic acid commonly used in cooking – has a pH range of between 2 and 3. Lemon juice also has a pH of between 2 and 3, mainly due to its citric acid and malic acid content. 

Meanwhile, battery acid – an aqueous solution of sulphuric acid – has a pH of about 0.8.

Neutralising brick acid

It’s important to neutralise any residual brick acid after cleaning masonry or a concrete surface. If you don’t, the acid may penetrate the brickwork further and damage it. When too many bricks become brittle, there’s a risk that the entire structure could collapse. 

To prevent this, always wash the brickwork thoroughly with water. You can also use baking soda or even a diluted solution of sodium hydroxide to neutralise any remaining brick acid. 

Safety and handling: usage, storage, and disposal of brick acid

Brick acid is highly corrosive and should be handled with care. It can burn your skin upon contact and may also cause respiratory problems if you inhale the fumes. To reduce the risk of injury, always wear protective equipment like rubber gloves, goggles, breathing apparatus or a face mask, and an apron. 

Brick acid should be stored in a locked cabinet, ideally in a shed or garage, and out of reach of children. Always neutralise any leftover brick acid before you dispose of it.


Brick acid is an aqueous solution of hydrogen chloride with a typical pH level of between 0 and 2. A strong and corrosive substance, it’s normally used to remove stains and mineral deposits from bricks, masonry and concrete surfaces. It’s important to neutralise brick acid after use to prevent the chemical from damaging the brickwork. As when handling any hazardous chemical, always wear protective equipment to reduce the risk of injury.


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