CONSTRUCTION: In the conventional method, when the colour of the leaves turns from green to pale brown then they are sorted out and split along their length after cutting off both the ends (see figure 1). The split leaves are then tied into bundles of about one foot diameter and immersed in water ('retting') for two days (see figure 2). After retting, the leaves are plaited to make thatch sheets (figure 3).
TREATMENT: 1. Dipping and Coating Method 2 Kgs of commercial copper sulphate is dissolved in 200 litres of water in a tank which is 7 feet long, 2 feet broad and 2 feet deep. The dry sheets are immersed in the copper suphate solution for 48 hours and then taken out to dry in the shade. The sheets are then coated with Cashew Nut Shell Liquid (CNSL) on both surfaces with a brush (see figure 4). Only a very thin coating is sufficient for the lower surface of each sheet. The sheets are dried in the sun, after which they are ready for thatching purposes. 2. Spray Method Mix 7 Kg of CNSL with 1 Kg kerosene and also prepare copper sulphate solution separately by dissolving 2 kg copper sulphate in 200 litres of water. Spray the copper sulphate solution twice on both sides of 200 dry thatch sheets at intervals of half an hour. The thatches are then stacked one over another, for 24 hours, and dried in the shade. The CNSL is sprayed on both sides of the thatches, with only a thinner coating on the lower surface. The thatches are then dried under the sun and later used for thatching. PRECAUTIONS: 1. Do not inhale copper sulphate spray since it is toxic. 2. Be careful while spraying kerosene as it is a fire-hazard. SOURCE: C.K.S. Pillai, R.R.L (CSIR), Trivandrum - 695 019, Kerala
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