Historically, limestone has been an essential building material for centuries. It is strong yet workable and fairly easy to find and extract, but it is also vulnerable to the elements which leads it to degrade over time. This process is inevitable and will nearly always require professional limestone restoration, but there seems to be a common misconception around what is actually happening and the difference between erosion and weathering.
The process of erosion entails tiny fragments of rock being moved by a force such as the flow of a river, the crashing of waves or to a lesser extent the wind. These tiny fragments will impact and rub against other rocks or a large piece of rock and the friction caused will result in minute damage to both surfaces. This damage will gradually build up over many years and eventually both moving rocks and the static ones will begin to change shape according to the erosion they have been suffering. This is why pebbles on a beach are smooth, they are constantly battered and rolled around, resulting in all of their sharp and pointy edges eventually being ground down to leave a smooth surface.
There are two main types of weathering that can occur: physical weathering and chemical weathering. Physical weathering is when an abrupt physical event takes place that forcibly breaks a rock or surface. A good example of this would be frost cracking; a process where water gets into gaps in a rock or surface and then freezes. Water expands when it becomes ice and as such it can force the rock apart and crack it open.
Chemical weathering on the other hand is far more subtle but has the potential to be equally destructive. This type of weathering occurs when a chemical reaction takes place between the stone and another substance, such as rainwater. The chemical reaction results in the stone being broken down and often dissolved. With rainwater and limestone, this is one of the biggest sources of wear as the water in the rain will chemically bond with the carbon dioxide in the atmosphere to form a very weak carbonic acid in the rain, which is perfect for dissolving limestone as it converts it into calcium bicarbonate, which will simply wash away.. This can be made even worse in areas of high pollution as there can be nitrogen oxides and sulphur dioxides in the air, which can form sulphuric acid causing acid rain.
These two descriptions should tell us that exposed limestone is going to be worn away by a variety of factors, but by far the biggest of these factors is chemical weathering. When applied to limestone buildings, chemical weathering can be highly destructive over many years, leading to the owners requiring the expert services of a company such as Kernow Stone to remedy the situation and repair the damage that humble rainwater is largely responsible for. Essentially, your limestone is being dissolved by the rain, and will need your protection.