How do you know if a stone is frost resistant and where to use it on a building?

Finding the appropriate material can be a daunting task if you don’t know what you are looking for.

During my career as a stone mason I have met customers, craftmen, and sometimes architects who were wondering which stone to use outdoors in the UK.

So I thought this post could help to avoid some expensive mistakes, and allow you to create your project with the most suitable stone.

What is frost damage?

A non frost resistant limestone absorbs water in tiny cracks which are invisible to the naked eye. When the water freezes it expands and behaves like a wedge being driven into the cracks.

In some stones, these spaces between the grain of the stone join up with each other, which allows the ice to come out of the stone. This is what we call open porosity and it is what makes some soft and porous limestone resistant to frost.

Compact stones with a fine grain break in irregular and angular shapes.

Stones containing a lot of clay will erode and crumble. Sandstone and granite will turn into sand and pebbles.

How do we know if a stone is resistant to frost?

To help us in our research, the EU has created in 2010 a new Regulation called NBN EN 12371.

A laboratory has tested each stone quarried in the EU. They do this by soaking a sample in water and leaving it to freeze then letting it thaw. After each cycle they measure its elasticity, compressive strength and visual aspect.

This regulation specifies that for using a stone as flooring it needs to resist at least 140 cycles.

What level of frost resistant stone is needed for outdoor projects?

For a non vertical feature or a stone protruding out of a building (cornice,windowsill),we need at least 84 cycles.

For an ashlar, we need 56 cycles and for a a vertical cladded ventilated stone we need 14 cycles minimum.

DS Stone Supplies Ltd will help you to choose which material to use safely, find a matching colour and supply it to your door for a competitive price. See our Stone Specifications for detailed figures on the frost resistance levels of our European limestone and marble.