What does acid wash mean?

Prior to sealing, your contractor may acid wash a stone floor or wall to remove any residue that has occurred during installation. It can also be used to remove efflorescence that has left a white residue on the surface of the stone.

It is common for pool maintenance teams to acid wash the interior of a pool to remove stubborn stains or calcium deposits once the pool is drained and scrubbed.

What does acid washing involve?

To acid wash a stone surface such as a driveway or outdoor entertaining area, the stone is wet with water before an acid mix is applied. The surface is then scrubbed with a stiff bristle brush or a commercial cleaning machine is used until the desired appearance is achieved. The process may be repeated, depending on the individual application and the extent of the staining.

As acid is a harsh chemical, it is recommended you start with a mix of 1:20 acid to water. Always test a patch in a discrete area before applying to your entire surface. If required, the ratio can be increased to achieve a heavier clean or the process repeated.

Once the surface has been thoroughly scrubbed, it is imperative that all the excess residue is washed off with water and it is allowed to dry completely prior to sealing.

Providing the mixture isn’t too strong, acid washing can also be used for a regular clean without affecting the stone sealant. It is recommended, however, to acid wash a pool no more than once a year as you’ll have to drain your entire pool and the process will remove a very thin layer of the surface. Too many acid wash treatments and your pool may need to be replastered.

What are the risks of acid washing?

If the acid washing isn’t done correctly streaks from the acid can permanently etch the stone or pool surface. If this occurs, this can permanently discolour the material.

It is important to ensure the acid wash mixture isn’t too strong, particularly when cleaning a stone surface as all products can react or burn. Some stone products, such as Raven Granite, is particularly susceptible to colour lightening when a strong acid mix is applied.

Speaking with your stone supplier and engaging a reputable contractor to acid wash your surface may be well worth it.