If you would like to know whether it is possible to apply the Moroccan, natural bathroom finish ‘Tadelakt’ to a modern material such as a clay block wall, then we have done some small tests just for you.
Tadelakt Test Conclusion…for those who just want the answer. Our small test on some blocks resulted as follows:
Yes you can. You just need to apply a natural clay sand finish to the clay block wall first. The mix is made from about 80% filtered (3mm) coarse sand and 20% (3mm filtered) clay and short cut straw. You can read a guide on how to make and apply that mix here
Tadelakt is a beautiful finish that is used in bathrooms and wet rooms, for sinks, showers, and floors too. It has an almost glass like feel to touch and doesn’t use any chemicals or harsh ingredients so will create a healthy environment in your home.
So first up we cleaned the lime plasters which were on the wall from a previous test. As hoped, they were really tough and needed a spade to scrape off.
Then we needed to prep the wall to receive the Tadelakt. This was the real test for me as we know the Tadelakt sticks to an earthen wall. The only question really was whether a thin layer of earth would be sufficient for the Tadelakt to stick to, and whether the earth would hold well to the clay blocks.
We used some clay slip to prime the walls (fine filtered clay mixed with water to form a nice paste. Quantities of water vary according to preference so don’t worry too much about the consistency).
Apply the slip generously with a brush to all the area you want to test. If you are doing this test for yourself then I would recommend going over the joints between the blocks as the materials may react differently here and could cause cracks which wouldn’t necessarily appear on the face of the block alone.
We made three new test areas. On the bottom left is left over cement from a previous test. We used this to have a go at applying Tadelakt directly over plastered concrete. The second from the left is a larger area of thinly spread Margarida Mix (75% filtered sand, 25% flitered clay, short cut straw and water). The third from the right on the clay block wall is a fat layer of Margarida Mix (about 2cm thick). And the final test in the models hand is on a standard concrete block we had laying around. Again we applied clay slip to the block first.
Both the clay and concrete blocks took the margarida mix without problems which was to be expected. In the previous test the cement render which is on the left also went on very easily. The real test will be how the Margarida Mix holds when subject to drying and some moisture. So we leave the tests to dry for a week or so.
As there was test patch of cement that had been there for some weeks now, it was ready to do a small test. We added some red natural colour to some old Tadelakt we had and pasted it on to the patch. It went on as easily as expected and stayed there. Again, we now need to wait to see how it holds when dry.
Once the margarida mix was dry I brushed it with a wet brush and applied the Tadelakt to it. It went on easily and stayed on with no problems.
In order to stop it from cracking, Tadelakt should be kept wet with a mister, and rub firmly with a very smooth stone. I didn~t have a smooth stone to hand so I used a yoghurt pot. The yoghurt pot technique is good for other earth finishes too, not just Tadelakt. It closes up the cracks and small holes to improve the water resistence.
With Tadelakt, you should also apply a soap for every day for the next couple of weeks, but if you want a full guide on how to make and apply Tadelakt then you best consult the professionals. This guide is just to see whether the Tadelakt mix stays on a modern building material.
So now we wait for some weeks to see how the tadelakt holds on the various surfaces.
And it held well. I cannot say for sure if it works in a bathroom over a whole wall as I have not tested it there however if it were my house I would feel pretty confident using Tadelakt on my clay block walls.
Mediterranean Permaculture 
Getting very technical
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