How to Fix a Damaged Cob Wall

A quick message before I begin, from a bioconstruction project in South Africa

We’ve launched a crowdfunding campaign to help finish building a training centre in early childhood development in one of the most dangerous suburbs in Cape Town.

We are busy building a passive solar, earth sheltered building out of tyres, cob, compressed earth bricks and glass bottles at the Delft Early Childhood Development (ECD) centre. But, we need your help to finish building it. The building will be an edu-centre so carers from informal crèches can get training in early childhood development.

You can donate here

Here is a really straight forward fix if you have a bit of non-structural damage on your cob walls. We had a section of cob which was falling off underneath one of our windows here at Eco Caminhos. The fix only takes about an hour, and here is how to do it…

First of all, what do you need?


As you can see above, there is only a few tools needed for this job. They are…

  • Large brush for wetting the wall and smoothing the wall
  • Burlap sack with natural fibres
  • Bucket of water
  • Clay slip (fine filtered clay with water added till it is a nice smooth paste)
  • Margarida Mix. We made this mix to smooth off our walls before applying the final render. The mix is made with 1 sand, 1 clay and short cut straw. Add water till it is a nice putty mix.


Next, pull off the parts of the wall that are really loose and won´t hold at all. Try to leave as much as possible though as it will make it easier to fix


Next, wet the wall. Use a brush to wipe the cob until a nice shiney layer of clay shows on the surface. This will give your filler and your sacks something to stick to.


Then take your Margarida mix, or whatever filler you use to smooth your walls, and work it right in to the wall. Sculpt the wall back to the shape you want it to be.


Using your hand, smooth everything off


ANd now the clever bit that keeps everything in place and really strong – the burlap sack. First of all wet the sack a bit then really soak it in your clay slip. Really work it in to the wall and make sure it is sitting there snug


Use a brush with some more slip if you like to paint the sack right in to the wall.


And there you have it, a really strong fix for your wall. You can use it over cracks, or just where areas have started to fall away from the wall. With cracks, just make sure to stuff your filler right in there before applying the sack.


Any questions or comments, please leave below here, or contact me through the contact page.

And for your viewing pleasure. Here are some scouts helping us fix our cob wall with burlap sacks

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