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Straw bale classroom: Lime render and clay plaster

02 Sep 14
Michelle Gaffaney
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Our straw bale classroom at Castle Hill School is really starting to take shape now!

The walls are up, the roof is on, and it’s time to start covering the walls.

The naked straw walls, before rendering.

Externally, we’re using a lime render to protect the building from the elements.

Lime is often used on straw bale and cob buildings and is a traditional building material. It is particularly suited to our harsh Yorkshire weather, as it has a sponge-lique quality, absorbing rainwater in bad weather, then releasing it, rather than allowing it to soak into the inner wall.

Here’s Arthur, our plasterer, tackling the first coat:

Lime render

Arthur lime rendering

The difference is astounding, and it’s so exciting seeing the classroom start to look more like a ‘real building’!

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Internally, we’re using clay – the oldest and simplest building material of all.

Clay is applied to the wall much like regular plaster, except that more coats will be needed. We start with layers of rough clay plaster, mixed with coarse sand to grip tight to the straw walls. Once this has built up, we apply a final layer of fine clay plaster (made using a finer sand) to give a nice smooth finish.

clay plaster