Preservative treatment may extend the service life of grass and palmyra thatches from 3 to 12 years. Besides treating the thatch, it is also necessary to treat the bamboos which are used for supports and the framework, and also the ropes/strings that will be used for binding.
Proportion of ingredients of the treatment is as follows :
(1) Fertiliser grade diammonium phosphate 99-95% (by weight)
(2) Sodium fluoride 0.05% (by weight)
Purpose
Diammonum phosphate acts as a fire-retardant chemical and Sodium fluoride as an insecticide as well as fungicide. As these chemicals are water-soluble, it is advisable to paint the thatch with the fire-retardant and then apply water-repellent paint over the treated thatch.
Procedure
(a) Impregnation of Thatch : Dry the thatch material by spreading it out in the sun. Prepare a 14% solution in water of the above combination of chemicals. Immerse the thatch material in this chemical solution and leave it to soak for 10 to 12 hours. Again dry it in the sun by spreading it out. Similarly, treat the bamboos and ropes/strings. Assemble the thatch roof in the customary manner.
(b) Protection Against Leaching : To make the treatment durable, the upper surface of the thatch is to be coated or sprayed with a fire-retardant and water-repellent paint. The following chemicals are required to prepare such a paint :
(1) Zinc oxide 15% by weight
(2) Mica Powder 15% by weight
(3) Talc Powder 15% by weight
(4) Chlorowax * 30% by weight
(5) Polyvinyl Acetate Emulsion 25% by weight
(6) Spirit in a quantity adequate to give the desired consistency for brushing/spraying.
* (Containing not less than 40% Chlorine)
Take Zinc oxide, Mica powder and Talc powder in BS 300 mesh size that is passing 53 micron sieve and mix thoroughly and add 30% Chlorowax to the above mixture in small lots and make a homogeneous paste. At this stage, add 25% polyvinyl acetate emulsion to the paste gradually and again mix till homogeneity is achieved. Add spirit which serves as a thinner, in sufficient quantity, for brushinglspraying. Store this paint in an air-tight container and apply the same to the roof.
Cost of Treatment
Ordinarily, a rural house has 25 m2 of area and the area of thatched roof will be about 32 m2. To make a roof of this size fire-retardant, the cost will be of the order of Rs. 250/- and this will, in addition, increase the life of the roof by about 10 years.
No comments:
Post a Comment