Earthbag wall and cob pizza oven part 3. Truth window and rendering the wall

Once the wall was finally built, the suspended concrete slab poured and the rocket stove built it was time to build a truth window and render the earthbag wall. I will update this post as I put successive layers of render on.

A truth window is often built into straw bale houses so that people can see how the walls were built. I decided to build one into the earthbag wall. I built a wooden frame and inserted lengths of reo bar in the back of it which were driven into the earthbags. After construction I taped up the front surfaces to protect them from any render that I might get on it. The window will have a hinged front with polycarbonate so you will be able to see how it was constructed.

truth window construction

truth window construction

truth window

truth window

For the rendering I would have liked to use a lime render but here in Tassie we have a lot of rain and it will be out in the openAfter m so after much research I decided to use a render ratio as follows

First coat:

  • One part cement
  • One part lime
  • 4 parts putty or plasterers sand (You need a sand that is angular and not rounded so that it locks together)

I soaked the lime for about two weeks in an old plastic dustbin. this ensures that the lime fully hydrates. Is is so fine that it takes time to take up the water. Wearing mask, goggles and gloves to protect me as lime is very alkaline and can burn I half filled the dustbin with water and then added the 20kg of lime. Using a drill attached paint stirrer I mixed thoroughly and then added more water as needed. Checked it every few days and stirred it well before use. Always leave an inch of water on the top to keep it well hydrated.

1st coat render

1st coat render

1st coat render 3

1st coat render 3

The first coat really started to fill in the gaps between the earthbags. I made sure that I cross hatched the surface so that the next coat would have a good key to stick to.

Second coat: I read that to help ensure that layers of render do not de-laminate that each successive layer should be weaker than the last. To this end I made the mix

  • One part cement
  • One part soaked lime
  • Five parts plasterer/putty sand

To ensure that cracking did not happen I added a layer of fibreglass mesh between layer one and layer two.  The mesh was about 200mm wide and I found this was a good width to render onto. Any big gaps between the earthbags were filled in before the mesh was put on. I kept the walls damp to slow the drying time as it was reasonably hot (even for Tassie). Note the edge of the render mesh in picture below.

2nd coat render 1

2nd coat render 1

close up render mesh

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