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Bush materials have many applications in building such as kunai grass and various types of palm fronds used as roof thatching. Also a number of types of woven wall linings such as kipa and bau-bau are in common use and bamboo is used in many different ways.
One of the main drawbacks of this type of construction and one which serves to defeat its advantage of cheap initial cost is the susceptibility to damage by insect and fungal attack and by fire. Because of this, many buildings constructed of these materials have a life expectancy as low as three years.
In an endeavour to extend the life of such structures, research work has been carried out in India, by the National Buildings Organisation, New Delhi and the Forest Institute, Dehra Dun. Treatments have been devised whereby the organic materials are impregnated with chemicals and it is claimed their life extended 5 to 7 times that which could be expected of them in the untreated state.
Whilst these treatments have been used by this Department, insufficient time has elapsed for us to be able to comment on their efficiency. It is on this basis that they are presented to the reader.
The first is a treatment to protect materials from decay caused by fungi and insects and the constituents are as follows: --
(i) Copper sulphate.
(ii) Sodium dichromate.
(iii) Acetic acid.
The solution is prepared as follows:
(i) Dissolve carefully 16 lbs. of copper sulphate and 18 lbs. of sodium dichromate in 40 gallons of water.
(ii) 15 ozs. of acetic acid should then be added to this solution.
NOTE: To facilitate the dissolution, crystals of copper sulphate and sodium dichromate should be broken down to pebble size and left in water overnight. Warm water also facilitates the dissolution. Acetic acid should be handled carefully to avoid burns.
The second treatment is intended to protect materials against fire as well as decay and insect attack
(i) Copper sulphate.
(ii) Boric acid.
(iii) Zinc chloride.
(iv) Sodium dichromate.
The solution is prepared as follows:
Dissolve 6 lbs. of boric acid, 2 lbs. of copper sulphate, 10 lbs. of zinc chloride and 12 lbs. of sodium dichromate one after the other in 20 gallons of water.
Preparation of materials to be treated should be as follows:
(i) The material should be left in air for some days to dry so that the moisture content of the materials is around 12 to 15%. Materials with more than 20% moisture content can only be treated with difficulty and would lead to a considerable dilution of the solutions.
(ii) If the material needs to be cut or shaped, it should be done before treatment, as far as possible.
(iii) Thatch is usually tied to split reeds or bamboos and these should be treated along with the thatch. Bamboos should be split and cut to finished sizes before dipping. If bamboo sections are to be used whole, a hole must be broken through each node membrane with a suitable rod, to allow access of the solution to the interior of the culm.
The method and duration of the treatment should be as follows:
(i) The leaves or bundles of grass, loose or loosely tied together should be dipped into the preservative solutions. These should be turned over occasionally so that they are wet on all surfaces and there is no hindrance to the absorption of the preservative. Full immersion of the material should be ensured.
(ii) Bamboos or reeds to be used may be dipped with the thatch or separately as convenient.
(iii) Before use, material should be air dried so that its moisture content is around 15%. This helps in fixation of the chemicals so that they are subsequently not so easily leached out.
(iv) For the first treatment (against decay and insect attack), the duration of dipping should be 6 hours for grass thatch and 24 hours for leaves.
(v) For the second treatment (against fire, decay and insect attack) the duration should be 32 hours for grass thatch and 48 hours for leaves.
Whether these treatments are effective when applied to the round bush timbers often used in this type of construction is not known. Experimental work is currently being done on this aspect by the Department of Public Works and the results will be published as soon as they are available.
Safety Precautions.
Whilst none of the chemicals used in these preparations are considered highly dangerous, certain safety precautions in their handling should be observed, viz.:
1. Avoid permitting acetic acid coming in contact with the skin, as burning can result,
2. Wash hands and other parts of body which have been in contact with the solutions, thoroughly with soap and water at the end of the day's work ar1d before eating.
3. Do not eat while working with solutions.
4. Do not smoke while working with solutions.
Half Drum : cheap and convenient when quantity of material to be treated is not too great.
Cut surface turned back can be used as platform for draining of solution from material after treatment and before final removal for drying, thus avoiding any waste of solution.
Cut half drums joined together to make bigger containers using wooden blocks for stability.
Bamboos or reeds to be used can be dipped along with thatch or separately as convenient. If bamboo lengths are more than container dip as shown and reverse to complete treatment.
(The foregoing appeared in Technical Research Bulletin, Vol.I published by the Public Works Department of the Territory of Papua & New Guinea, October 1964)
Letter from Public Works Dept., T.P.N.G., to O.I.C., Siassi Patrol Post, Morobe District, dated 26th March 1969 :
Your 10-2 refers.
Enclosed are drawings you have asked for of lime kilns, charcoal retort, and loom for weaving sago bark matting.
A further technical bulletin is in the preparation stage now; staff deficiencies at this station have made earlier publication impossible.
This Department does not handle chemicals for the maintenance etc. of semi-permanent or "native" materials buildings. The chemicals listed in the Technical Research Bulletin No.1 can be purchased from any pharmaceutical chemists, or possibly agents of chemical companies.
Of further interest however, the following may be useful to you as treatment for kunai thatch, using:-
The solution is prepared as follows:-
Dissolve 6 lbs. of Boric Acid, 2lbs. of Copper Sulphate, 10 lbs. of Zinc Chloride, and 12 lbs of Sodium Dichromate, in that order, in 20 gallons of water.
Preparation of materials to be treated should be as follows:-
The method and duration of treatment:-
During treatment all solution should be thoroughly removed from body and hands of the operator with soap and water. Do NOT eat or smoke while working with the solutions.
Half 44 gallon drums welded in series make ideal containers for treatment.
The above treatment should effectively extend the useful life of kunai thatch 5 to 7 times that of untreated grass.
(signed)
for T.M. CROTTY
DIRECTOR