Thannal Natural Building Workshop Dec 2015

Mixes & Recipes

Foundation Mortar Mix

2.Surkhi ( Brick dust/fine fired clay powder)
3.Quarry Dust
5.Fermented Mix
Equal quantities of all the above mentioned ingredients were mixed and kept for fermenting for minimum 10 days. Care has to be taken to keep the mix covered with Jute bags and we need to keep pouring the fermented mix (Kaddukai + jaggery) everyday to keep the mix moist.
Notes: In our site we used a tractor to blend the mortar mix, you can alternatively use an idly grinder for mixing the ingredients. This is done to increase the strength of the lime in the mix.

Kaddukai-Jaggery Fermented Mix

1.Kaddukai Fruit, also known as Gallnut, Haritki (Terminalia Chebula)
2.Palm Jaggery. Sugarcane jaggery can also be substituted but the former will give a better result.

1.Kaddukai (crushed): 8 Kgs.
2.Palm Jaggery :8Kgs
3.Water : 200 Li
The Kaddukai fruits have to be broken up with a hammer. We need to measure out equal quantities of the broken Kaddukai and Palm Jaggery (8kgs each) and keep it in a Jute bag whose mouth can be then sealed. This bag is then carefully immersed in a 200 Li barrel filled with water. We need to keep this to ferment for a minimum of 10 days before this can be used for mortar. The fermented mix can be directly used while making mortars, as a substitute for water. The advantage of using the above fermented mix is that it acts as a good binder for the mix. Also due to the molasses process the Mortars have a higher strength.
Note: Tie the Jute bag with a long stick so that the bag does not settle down but stays submerged in the water. This water can also be used in the cob mix.

Cob Mix

1.Red Soil or the local soil in your region.
2.Straw, finely chopped about 3” short.

1.Local Soil : 10 Parts
2.Straw : 2.5/ 3 Parts
3.Water : Just enough to get a doughy consistency.
The Red Soil in our site was locally sourced soil and was found suitable for the cob mix without any additions. It is, however, advised that the soil be tested before it is used in making any mix. There are many methods of testing a soil, the easiest one being the Bottle Test that we had displayed in our Material Library. For this we just need a clean transparent glass bottle; fill 3/4th the bottle with soil and pour water into the remaining bottle. Put on the lid and shake vigorously, then let it settle; you need to wait till the layers of the soil settle perfectly; this may take hours and sometimes days. One can gauge the percentage of each component by observing minutely, the top most layer will be humus, followed by clean water, then clay, silt and sand respectively. The clay content of the soil must be at least 20-30% and that of the sand 50-60% for a good mix. If either of the content is more or less, some clay or sand must be added to get the optimum ratio.
Note: You can also get your soil tested in a lab, to get its precise composition.

Bamboo Treatment

Bamboo Selection
For column we need to select a strong thick walled dry bamboo. Whereas a thin walled bamboo can be used for construction of wattle and Daub. Bamboos with thin walls are easier to split thus they can be efficiently split and bent as walling members. These bamboos can be used directly after treatment as they are more flexible when wet.

Boric-Borax Treatment
1. Boric Acid
2. Borax
3. Water

1. Boric Acid : 1 Part
2. Borax :1.5 Part
3. Water : 100 Li
We need to dig a pit big enough first, to accommodate the largest of your bamboos. The pit must be carefully lined with tarpaulin sheets to prevent the solution from draining. After the pit is dug it is easy to calculate the quantity of water by calculating the volume of the pit. Then we can carry out reverse calculations to arrive at the quantities of the Boric- Borax required.
Simultaneously holes (4mm dia) must be drilled onto the bamboos. Care must be taken to drill the holes 1-2” above each node. This will allow the Boric-Borax Solution to enter the inside of the bamboo and render the starch inedible for the potential pest (Boring Beetles).
The Boric Acid is available in a powder form (Boric Powder). Boric Acid is made from Borax which is a naturally occurring salt. Both the ingredients are mixed in the given proportions with warm water in a small bucket first to dissolve the salt and remove all the lumps before adding to the pit filled with water. We can do this in small batches.
After the solution is made the bamboo must be carefully dipped into the solution. Care must be taken to immerse the bamboos completely; we can place long stone slabs onto the bamboos to make sure that they are completely dipped.
The bamboos must be treated with this solution for at least 15 days before they can be used. After the bamboos are removed from the solution, they need to be dried, by keeping them vertical in a shaded area.
The bamboos used as columns should be coated with Bitumen up to the plinth level.

Note : The split bamboos used for the wattle and daub can be alternatively coated with lime slurry where treatment with Boric-Borax is not feasible.

Plaster mixes

1.Red Soil or the local soil.
2.River sand /Borewell Dust
3.Straw (very fine) /Rice Husk
6.Refined Flour (Maida)


NoRed soilSandBore well DustStraw/Rice HuskCaseinManureMaidaLime
212241 small cup1
3122412 small cup

The above are proportions that we have worked out during the workshop. Any updates regarding the change in the proportions of the mixes can be followed up on our web page. Website- www.thannal.loc

Note: The composition of soil will vary in every region and so will the mix proportion. The above mentioned mixes and proportions have been tried and tested on our site. These are not be taken as rule of thumb, many trials have to be carried out before finalising what is the best mix for the soil available in your region.