How to protect sandstone

Sandstone is an iconic feature of Australian landscape design and construction.

Sandstone has been used as a construction material in building facades and landscapes for hundreds of years. Some of our most iconic buildings and landscapes are made almost entirely out of Sandstone. You don’t have to go far in Sydney to see incredible examples of just how beautiful and versatile this material can be. Buildings like the QVB, Sydney Uni, Barangaroo Foreshore and the Cove are all testimony to this great natural resource. However, without proper care, the serviceable and aesthetic life of Sandstone can quickly be compromised. Sandstone has one major enemy and that is, water! When Sandstone is left unprotected water enters the stone and carries with it, salts, pollution and organic matter. The water then evaporates leaving behind the pollution that weakens the stone and makes it look unattractive. It leaves behind the organic matter that feeds off the damp stone and turns into mould and mildew. It leaves behind the salt that crystallizes, and when it crystalizes, it expands and destroys the surface of the stone.

Salt attack

Salt attack is most often seen in pool surrounds, landscape gardens and building facades in coastal areas. George Dodd from the Sydney Uni wrote this excellent article recently highlighting the challenges associated with preserving Sandstone surfaces in coastal areas. “Preserving the history of our precious sandstone buildings”

Salt attack affects some sandstone much more than others. The first effect seen from salt water ingress, is the oxidization. This is where we see the stone take on a slight reddish/orange tinge. This is actually a form of rust occuring as the salt water comes into contact with minerals in the stone. The next thing we see will be the surface of the stone becoming rough and more porous. This is followed by extreme pitting of the surface and in some cases the entire surface skin delaminating from the stone. Learn more about these modes of decay in this brilliant article written by Jim Mann from Stone Initiatives – “The resistance to salt attack test”

The solution

Extensive testing has proven, that the most successful protection system for Sandstone is a consolidator and water repellent combination. Defender CSD50 is a prime example of this type of product. Defender CSD50 reacts with the stone to harden and densify the surface while also imparting excellent water repellency. Some of the unique advantages provided by this product, is that it does not change the appearance of the stone at all and the protection is permanent. Not only does the sealer protect the stone from water, mould and salt attack, but due to the strengthening effect of the consolidation technology, the stone is also protected from aggressive high-pressure cleaning systems used by councils and cleaning contractors.

The images below, clearly show the difference between Sandstone that has been protected with Defender CSD50 and Sandstone that has been left unprotected. The Sandstone blocks were supplied by Gosford Quarries. One block of each colour stone was treated with Defender CSD50 and the other left untreated. All the blocks were the subject to standard salt-attack tests. Testing requires 14 (12hour) cycles of submersion in salt water solution, followed by drying at 60°C. The experiment that we carried out was approached in this exact manner. following the 14 days, we continued the experiment for a further 120 days. The blocks marked with a 1 Were left untreated. The blocks marked with a 2 were treated with Defender CSD50. The piles marked with a 3, show how much material was lost off the untreated blocks during the course of the salt attack testing.