Cleaning stone or masonry is important in improving a building’s appearance, removing anything that could damage its structure, and restoring the natural stonework. However, certain cleaning methods can do more harm than good. Pressure washing is often considered a quick and easy way to clean most outdoor surfaces and remove paint from stone or brickwork. However, it can cause untold damage to the interior and exterior walls and could lead to paint chips blasted across the building’s surface and surroundings.
Risks of pressure washing to stone and masonry
Using a pressure washer risks removing the natural patina of masonry and stone surfaces. It can also take away any coating or sealants previously applied to the building. This will open up the pores in the surface and allow water to seep deep into the stone and masonry. It’s also common for people not to put tips on the pressure washer to help remove deep soiling. However, not placing tips on a pressure washer can lead to severe scarring of the building’s surface, leading to deep patterns becoming carved into the stone or masonry.
People often choose to use chemicals to help remove excess soiling during pressure washing. These chemicals may include bleach, acids and high alkaline cleaners. The pressure washing process can push these chemicals deep into the stone, causing irreversible damage.
Damage caused by over-saturation
The higher the pressure setting, the more water consumed by the stone or masonry during pressure washing. When stone or masonry becomes over-saturated it will develop efflorescence, leaving a white powdery residue on the surface. This powder contains salts from the stone and setting material. These salts dissolve and deposit onto the surface, leading to flaking, pitting and delamination.
There’s also the risk that once the water gets into the wall, it will take a very long time for it to evaporate. This excessive moisture within the wall can jeopardize the external and internal structure of the building. In addition, pressure washing can remove grout and point on a building’s exterior. Grout and point can become soft, weak and cracked over time. The over-saturation caused by using a pressure washer will accelerate this process.
Effective alternatives to pressure washing
When it comes to cleaning stone or masonry on the façade of a building, you should always leave it to a professional to ensure safe and long-lasting results. A professional will carry out a pre-cleaning survey to identify the type and cause of soling and whether it has caused any damage or decay. The surveyor can also determine the softness of the exterior surface, particularly the grout and point. Pre-project cleaning test trials will then be used to decide the safest and most effective cleaning method.
While there are several different approaches to cleaning stone or masonry, the type of soiling, age of the building and results from the pre-cleaning survey will help determine the most appropriate. Some of the most common protective and conservationist techniques for cleaning stone and masonry include:
- Rubbing and brushing, wet and dry abrasives or surface dressing
- Sponging, water sprays and steam cleaning
- Organic solvents, acidic or alkaline treatments
- Laser cleaning and ultra-sonics
- Sandblasting
- Low-pressure cleaning
We are conservation driven in our philosophy and approach to masonry cleaning and building restoration, with experience on a range of historic and listed stone or brick buildings. If you’re looking at getting your building professionally cleaned or restored speak to one of our experts today.
