To make existing mud walls water proof, the following procedure is recommended :
Addition of Chopped Straw
Chopped straw of 20 mm length and 2 mm wide should be prepared in large quantities. For every cubic metre of dry mud mortar, prepared as described in the earlier para, 64 kg of chopped straw is added and thoroughly mixed. The mix is shaped into a circular arc and water is filled in the centre space so as to keep it constantly wet for 10 to 15 days. The mortar is kneaded every day manually (by feet) and turned over by shovel, two or three times a day for a period of 10 to 15 days. The chopped straw will become soft by the above treatment and it will improve the cracking resistance of clay.
Preparation of Bitumen Cut-back
Bitumen of 80/100 grade penetration and kerosene oil are mixed in the ratio of 5 : 1 for preparing the cut-back, i.e. 53.25 kg of bitumen and 10.5 litres of kerosene oil for every cubic metre of soil. Bitumen IS slowly added to the kerosene oil which is kept in a separate container, keeping the whole mixture stirred until the whole of bitumen is added. 15 gm Beeswax is heated in a separate container and added to the bitumen mix and stirred thoroughly. The addition of wax increases the shelf life of the emulsion.
Preparation of Non-erodable and Water-proof Mud Plaster
The bitumen cut-back so prepared is added to the mud mortar prepared earlier. The required quantity of cut-back is taken from the container and it is spread over the heap of mud mortar uniformly, and worked up with a spade several times to ensure its throughout mixing. When the plaster is ready for use it will show good work ability, gloss and plasticity.
Application of Mud Plaster
The wall must be scrapped free of dirt by trowel to give it a uniform surface. Existing cracks must be filled with ordinary mud slurry and allowed to dry. Water should be sprinkled on the wall before the application of mortar. The plastering is commenced from the upper portion and the work should proceed towards the bottom. Apply the plaster in 12 mm to 15 mm thickness with a wooden trowel and finish smoothly. When the plaster is drying, sprinkle water occasionally.
Application of Cowdung Slurry
One part of cow dung and one part of soil are mixed and water is added to form a thick paste. To this paste, bitumen cut-back is added in the ratio of 1 : 24 by weight, and mixed thoroughly. Cow dung slurry is applied and finished with a wooden float. This coat is effective in filling the hair cracks and voids in the plaster and stops further development of cracks.
Cost
Due to the increasing cost of bitumen and kerosene the cost of this treatment may be as high as Rs. 10 per m2, A rural house may have normally 40 m2 of outside wall surface and the cost per household adds upto Rs. 400/-; however, the durability of the house will increase several fold.
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