Lime vs cement

Why do we use lime for the footings, foundations, floors, render and mortar in a cob house?

  1. A cob house, cob-bale house or any natural home needs to breath: one of the pluses of building your house from cob is that you should not experience damp or mould problems. This is because moisture can escape from a cob house through the earth walls. There is no opportunity for water to build up and cause problems. This makes for a house that is structurally and aesthetically superior and healthier to live in. To ensure the cob walls and floors remain breathable it is important to use clay and lime plasters on the inside, a limecrete floor, and a lime render on the outside of the house. Lime is breathable. In contrast, cement does not allow for the escape of moisture. It acts as a barrier. If you live in an old earth house and you currently have cement render outside or inside on your walls it is important to remove this. The cement will be trapping water in your walls and this could effect their stability. We specialise in replacing cement renders with lime on period properties. Please visit our renovations page for more info.
  2. Lime is flexible- you will have seen on most conventional new builds you always get some cracks on the internal plaster and on external cement render after a while. This is because cement is inflexible. In contrast lime allows a certain amount of movement and settlement to take place in your new cob house so you won’t see the cracks you’d get with cement.
  3. Lime is much kinder on the environment with lower CO2 emissions than cement – converting lime stone into usable lime products for the building industry produces a lot less CO2 than cement productions – partly because lime does not need to be heated to such high temperatures. But the best bit of all isl, as your lime render, limecrete or lime mortar sets, it carbonates in the air. This means it takes back CO2 from the atmosphere. How cool is that? It is estimated cement production accounts for at least 5% of global CO2 emissions and so using lime instead is one important way of helping reduce global warming.

The Guardian did a very informative article titled ‘Lime is a much greener option than cement’ about the benefits of using lime. You can read the article here. If you choose to come on one of our cob house building courses we will also take you into much more detail about the different lime products you can use (hydraulic lime, slaked lime etc) and how to use and apply them.