Lime as a Fire Resistant Building Material

Lime as a Fire Resistant Building Material

Lime is a popular fire protectant building material for many reasons. It’s attractive, durable and can be used in both indoor and outdoor projects. However, limestone is not just any ordinary stone, it’s an excellent fire-resistant material with many unique properties. These properties make it an ideal protectant against heat damage.

In this article, we’ll discuss how these properties make lime a great choice for protecting structures exposed to high temperatures. Also, what makes lime different from other materials on the market today and why you should consider using lime in your next project!

The Composition of Limestone

Limestone is a sedimentary rock composed of calcium carbonate. The material has been used for centuries in construction, and it is often thought that limestone is a porous material and might not seem to be ideal for construction. This is a misconception.

The porosity of limestone can actually be an asset. This is because it’s easy to cut into different sizes and shapes. Limestone also has a high resistance to weathering and water erosion. It is an excellent choice as an exterior stone or interior wall cladding material.

Mohs, The Hardness Rating

As a material, limestone is a tough mineral. Similarly, to iron, limestone has a Mohs hardness rating of 4. This means although it can be scratched with sharper blades it is by no means delicate.

Why is Lime Fire Resistant?

The reason you’re here, protection against fire and heat.

It was not until the middle-ages that plastering in Britain really took off. Open fires and timber buildings covered in reed were still extremely common. As you can imagine, this was not a great mix and so fires were a big problem for medieval Britain. A traditional lath and lime plaster ceiling can protect the timber joists therefore preventing or delaying flames from rising quickly through the building.

Important to note, all lime mortars and renders are non-combustible. A classification rating of A1 resistance to fire has been given to all lime mortars and renders. This is in accordance with BS EN 13501-1. If you need more information on fire classifications then visit

Anyway, plaster had started to become known throughout Europe for its ability to protect against fire. In the late part of the 12th Century, Henry Fitz Alwyn, the first mayor of London ordered that all cook shop sites be plastered.

In 1212 there was a huge fire which destroyed many buildings along the Thames and spread onto London bridge. The bridge had recently been rebuilt in stone so it survived but houses that had been built along it which were supposed to help pay for its maintenance were all destroyed.

King John endorsed Henry Fitz Alwyns order by declaring that shop owners around the Thames and London bridge must whitewash and plaster inside and out any house covered in reed or rush within 8 days or it was to be demolished. He further ordered that all houses in which brewing or baking is done be plastered within and without so that they be safe from fire. Years later, limestone is still as good at reflecting back heat even if it cracks open.


Lime is one of the most common building materials used in the world today. It has a long history as a construction material and is still widely used today because of its durability, strength and heat resistance.

Lime is highly effective at protecting buildings against fire damage. This is because of its high heat resistance and class A1 rating of fire resistance.

About Ecoright

Ecoright have been working with architects, housebuilders and specialist brickwork contractors for many years, so their knowledge of lime and its uses is extensive. If you have any questions about how to use lime or its suitability to a particular project, please get in touch, they will be pleased to advise. You can read more about Lime Renders here:

Lime Renders are available through Ecoright’s sister companies:

Lime Render – the natural choice for exterior and interior work Lime Render – the natural choice for exterior and interior work

Lime mortar is highly aesthetic and can be exact colour-matched to bricks or other adjacent materials making it a good choice for conservation or new build.