Sandstone is a common building material in many parts of the world. Sandstone is also subject to several different forms of weathering, which wear it down over time.
One process that weathers sandstone is ice crystallisation, which is sometimes referred to as "ice wedging" or "frost wedging." This occurs when water seeps into a pore or crack in sandstone and then freezes. Because water expands when it freezes, it has the potential to fracture sandstone and break pieces off.
The process of salt crystallisation is similar to ice crystallisation, though in this case it is a saline solution that enters a crack in the sandstone and then crystallises and expands. This produces a wedge effect, and can widen cracks in sandstone and break pieces apart. Often, ice crystallisation and salt crystallisation work together to weather sandstone.
Expansion and Contraction
Constant cycles of expansion and contraction can also weaken sandstone over time and eventually cause it to break apart. Expansion and contraction of the molecules in sandstone occur when it heats and cools (as it does from day to night, especially if the sun shines directly on it), and when it is wet and then dries.
Lichens can also weather sandstone. When lichens grow on rock, they produce a chemical that breaks down stone and allows the lichens to obtain nutrients. Lichens will eventually make cracks and holes in sandstone that make it more susceptible to other forms of weathering.
In general, the more holes, pores or cracks there are in a piece of sandstone, the more susceptible to weathering the sandstone will be.