Cleaning natural stone paving can be a precarious task. Different types of natural stone have different properties, so different methods are needed to clean them. We regularly receive calls from clients who need to clean of cement residue left over from pointing. One product which will remove cement is called lithofin builders clean. This is an acid based product which works well on sandstone paving. It is important to follow the manufacturers instructions before using any acid based products. Acid should NEVER under any circumstances be used on any type of limestone paving. Using acid on limestone will completely ruin the surface colour of the stone. We have used acid before when cleaning excess grout from slate paving but it was heavily diluted.
Another thing to avoid is jetwashing natural stone. A jetwash is an effective way of cleaning stone but at the same time it can cause damage by blasting away the surface particles of the stone. Jetwashing will clean natural stone in the short term, but in the long term will make the stone more porous and difficult to keep clean. Softer sawn sandstone is particularly susceptible to jetwashing. If you do need to jetwash make sure that the jetwash is set on a low setting and do not hold it to close to the stone. A good way of cleaning stone is to use a bucket of hot soapy water and a stiff brush.