Natural stone is one of the world’s oldest building materials, and its attractiveness, strength and durability have ensured it is still as popular today. But whether York stone, Bath stone or any other type of natural stone, it can become damaged by ageing, extreme weather, and pollution. When done correctly, cleaning natural stone will help to preserve the building’s beauty and ensure it will continue to serve you for many years. However, while stone might be durable, incorrect cleaning methods can cause considerable damage either immediately during the cleaning process or some time afterwards.
Before you go ahead with cleaning natural stonework, make sure you know the type of stone it is, what kind of staining you are dealing with and the most effective and safest cleaning method for the stone.
Why clean natural stone?
Cleaning the stonework of a building improves its appearance, removes any impervious paintwork, and can help to blend the original stonework with new work carried out such as repairs or an extension. It is also essential for the overall structure of the building. Vehicle exhausts release nitrogen dioxide and sulphur dioxide into the air which reacts with the stone to form calcium sulphate. If not washed away by rainwater, these crystals will trap the polluted air particles producing a black crust, causing the stonework to deteriorate, triggering blisters and spalling of the surface. The effect of limestone decay is particularly severe along heavily trafficked roads.
Cleaning natural stone helps to slow down the damage caused by deposits on masonry and will reveal the overall condition of the stonework where the deposits have concealed cracks, failed pointing, damaged stonework, or serious structural faults.
Pre-cleaning survey
Before any stone cleaning begins, a survey of the building should be carried out to provide crucial background information on its style and construction. This survey should also take into account any conservation objectives. For instance, if the building has certain marks that reflect its age, this may need preserving. A pre-cleaning survey will identify the type, pattern and cause of the soiling and examine the building’s structure to see whether the soiling has caused damage or decay. These issues will all need reviewing within the context of the building itself, its history, location, construction and proximity to other buildings. The findings in the survey may decide the method of cleaning the building’s stonework is required, where and how.
Natural stone cleaning methods
There are several different natural stone cleaning methods. However, the type of soiling, the pre-cleaning survey and pre-project cleaning test trial will determine the most appropriate form of cleaning. Some of the techniques commonly used 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
Some cleaning methods such as dry air abrasion, high pressure or continuous water spray can damage delicate stonework such as soft Bath stone if not carried out correctly by a professional. See our blog post Choosing the best cleaning solution for your stone building for more information.
Benefits of steam cleaning
Hot water cleaning, low-pressure cleaning, and steam cleaning are one of the safest methods of restoring and maintaining soiled building façades and exteriors made from natural stone such as sandstone, limestone, slate, or quartzite, and other natural stones. This process effectively removes staining such as traffic film, carbon, leeched salts, effluence staining, organic matter, environmental pollution and paint from the natural stonework. When just the right amount of pressure is applied, steam cleaning will remove dirt, and debris and restore a building’s natural stonework to its former glory without the use of harsh chemicals.
Choosing the correct method for cleaning natural stone will help to preserve this precious piece of history and ensure the building continues to look its best for years to come.
