Brick acid is often recommended as a patio cleaner, especially for stains on natural stone paving. But it can cause more problems that it solves. We look at the dangers of using patio cleaning acid on natural paving and what precautions you should take.

Close view of dirty riven sandstone paving with twigs and leaves.
With the correct patio cleaner, this riven sandstone paving will look like new.

When to Use Acid Cleaners on Natural Stone Paving

Acid-based formulations are not recommended for general cleaning of natural stone paving. And they should never be used, in any circumstances, on calcareous stones like limestone, marble, and travertine. This is because the acid reacts with the stone to create irreparable and unsightly damage.

However, the following situations may warrant the use of acid natural stone paving cleaners on non-calcareous stones like granite, slate, or sandstone.

  • Efflorescence: to dissolve and remove white, powdery deposits caused by soluble salts.
  • Rust stains: to eliminate rust stains caused by metal structures and by oxidation of iron traces within the paving.
  • Mortar or grout residue: to dissolve and remove residue left after installation or repair work.
  • Mineral deposits or hard water stains: to break down and remove deposits that cause a dull or discoloured appearance.
Bottle of Lithofin Bero rust remover and stone cleaner, acid-based
Lithofin Bero is an acid-based cleaner for rust marks. An alkaline formulation like Lithofin Rust-Ex should be used for limestone.

The dangers of acid-based patio cleaner

The following can all be caused by mis-use of acid-based cleaners.

  1. Etching. Acid can react with the minerals in the stone, causing the surface to become rough and pitted. This etching can lead to an uneven appearance and texture, which can also make the stone more susceptible to staining and damage.
  2. Discolouration. Acid cleaners can alter the colour of natural stone by reacting with the minerals in the stone, leading to undesired colour changes, fading, or uneven colouration.
  3. Loss of shine. An issue that affects cleaning interior tiles more than exterior, etching caused by acid-based formulations can dull the polished or honed finish of natural stone, leading to a loss of shine and a less attractive appearance.
  4. Weakening of the stone. Prolonged or repeated use of acid-based cleaners can weaken a stone's structure, making it more susceptible to cracks, chips, or other forms of damage.
  5. Increased porosity. Acid cleaners can increase the porosity of the stone, making it more vulnerable to moisture penetration and staining, which can eventually lead to the growth of mould or mildew.

Precautions to Take When Using Acid Cleaners on Natural Stone Paving

To avoid these negative effects, it is crucial to use cleaning products specifically designed for natural stone or opt for neutral pH cleaners. We recommend that you consult your stone supplier or a professional before using any cleaning product on your stone paving.

Tub of Dry Treat Alkaline Cleaner, suitable for all stone and porcelain paving,
Dry Treat Alkaline Cleaner is safe for all stone and porcelain paving, and can be used for a multitude of stains.

If a patio cleaning acid is appropriate, and recommended for your specific stone type, follow these guidelines to ensure safety and prevent damage:

  1. Read and follow the manufacturer's instructions for proper dilution, application, and dwell time.
  2. Test the cleaner on a small, inconspicuous area before applying it to the entire surface.
  3. Wear appropriate personal protective equipment (PPE) such as gloves, eye protection, and a mask.
  4. Ensure proper ventilation if working indoors.
  5. Apply the cleaner evenly, avoiding pooling or over-application.
  6. Rinse the area thoroughly with clean water after the recommended dwell time.
  7. Dispose of waste properly.
  8. Monitor results and reapply the cleaner if necessary, following manufacturer's guidelines and professional advice.

It’s inevitable that there will be spills and stains on your natural stone paving during the course of its life. With care, they should cause no problem and we recommend that you use a patio cleaner specially formulated for the stains you wish to remove.

Post updated: March 2023