Finish for Adobe and Cob

The finish layer with clay requires some preparation worthy the end result it provides. On the photo below is an Adobe wall recovered by a clay finish and clay painting.

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You may use two types of dung to make your finish; cow or horse dung. Cow manure has hardening enzymes although horse manure provides with very good fibers for your plaster cohesion. When using horse manure you may add wheat floor to make your finish harder.

My choice in this case is about resource availability. In the region no one use horse dung as an organic fertilizer for two reasons;

– Horse manure needs to be composted because high in nitrogen (due to the method of gathering which implies a mix with horse urine in the stable). Cow dung can be used as is as a fertilizer.
– Horse are given a lot of dewormers in the tropics, something you do not want in your compost. Only antibiotics are well degraded in the hot composting process.

Therefore horse dung is better used for adobe than for compost, and easy to find and get from farms. They can be gathered as well from the sand road when you are lucky enough to live in a place where horse riding is part of the local culture. You do not need important quantities of horse dung to make a finish.

If you get cow manure better to use it for your kitchen garden.

The proportions to make a finish mix are as following;

– 2 Bucket of horse dung
– 4 Bucket of mixture sand/clay in proportion of 20% clay / 80% sand
– Optional : 1 kg of flour

You may test the clay/sand mixture by applying a fine layer on a wall and see if it’s cracking. In this case add some sand.

Clay processing

The clay should be sucked in water to ease the filtering process. A very fine meshing is required.

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The mixture you get is very liquid.

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You may gather it in a bucket and wait 2 to 3 days for decantation. The excess of water will surface and can be easily removed from the bucket.

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You obtain a very fine mixture with a low proportion of sand (only very fine sand pebbles have gone through). This is the main reason you need to add sand although your soil could be already in the correct initial proportion of 20% of clay and 80% of sand.

Sand processing

The sieve for sand needs bigger meshing. The sand needs to be dried so to ease the filtering process. It is worthy to store some sand in a location ventilated and protected from the rain one week before.

Dung processing

The dung needs to pass through a sieve as well, with bigger mesh. The filtering process separate long fibers from the short one and help as well to obtain an homogeneous material. From the different tests performed it does not appear a real difference between using old and dry manure or fresh one. When the final mixture is kept wet for few days the enzyme activity improve the hardening of the plaster in any case.

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The residues of dung and clay can be mixed together (in proportion of 1/3 volume of dung and 2/3 volume of clay residue) to be used as a rough (still strong, thanks to the dung) mortar to fill holes for examples in location which need a better mortar. Usually the clay residue has higher proportion of sand which did not go through the sieve.

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Flour processing

This step is optional and should be dedicated to the parts of your walls where you need a very fine and strong rendering.

Whisk flour in 2 liters of cold water. You’ll obtain a white and consistent paste than can be diluted in 4 liters of warm water. The dilution can be done by passing first the paste through a large mesh into the hot water in order to remove the clumps.

Mixture

The mixture can be done in a large recipient.

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The color will become grayish, a bit like cement. If you put color pigment here be aware that you’ll need a big quantity of it and that the gray influence of the dung will ruin a bit the end result. If you want to have a colorful wall it is better to make a painting coat using clay as well.

Mixture for painting

The proportion are

– 1 Bucket of clay
– 1 Bucket of sand
– 1/2 kg of flower
– Color pigment powder; (you may mix various pigment to obtain the taint you desire)

Make sure you always use the same proportions of mixture and pigment in order to avoid color variations on your wall. The sand, this time, should be passed through a finer mesh than for the finish. When finished the paint can be dried under the sun and transformed in a powder for future use.

Applying the clay finish

Before to apply the finish you need to make sure that your wall is dry since the finish is more water proof and could prevent your wall to dry or at least slow down the drying process. Then you pulverize water on the part where you want to plaster and scratch the wall to increase adhesion.

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Fine finish can be obtain using a flexible spatula (you may use a piece of plastic from a detergent plastic bottle like in the photo below). It is always possible to water a previous work and rework the finish. An advantage of such technique.

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The end result before painting is as following;

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When painting the wall put 2 layers of paint, it will make a difference.

The wall should be dry before painting.

When passing the paint make sure it fills in the holes. Wait another day to pass the second layer of paint

When doing wall sculpture you should add layers of 2 or 3 mm max on top of each others to create relief and wait for the previous layer to dry every time.

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