BRIGHTER BUILDINGS

Evening Star, Issue 22444, 15 September 1936, Page 2

BRIGHTER BUILDINGS

USE OF EXTERNAL CEMENT HEED OF PRECAUTIONS New Zealand builders and architects, following the examples set ip older countries, are giving a bright finish to various structures by the use of coloured cement. In the case of renderings on brickwork it is necessary to give heed to the composition of the bricks, according to an official report contributed by the British Building Research Station to the journal of the Royal Institute of British architects. It is mentioned that external cement renderings have in the past been liable to a great many troubles of one kind or another, crazing, cracking, discolouration, and even in some cases efflorescence.’ It sometimes happens, when a cement rendering is applied over brickwork containing an abnormally high proportion of sulphates, and particularly when the design of the building and the conditions at the time the work is carried out are such that water gains access to the brickwork, that the sulphates attack the cement in the rendering, and when this happens the rendering disintegrates completely and ultimately may fall away from the wall, leaving a mushy paste on the face of the wall which is usually found to consist mainly of calcium sulphate. It is often found in such cases that repeated attempts to renew the renderings are unsuccessful, and finally some very expensive and complicated treatment is necessary to obtain a dry wall of reasonably good appearance. In the last 10 years a considerable number of failures of this kind has been investigated by the Building Research Station, perhaps some 20 in all. While it is not suggested that the trouble is a very common one, yet, nevertheless, when this type of failure does happen it is so. exceedingly troublesome that it is felt that the attention of the industry should be drawn to it.

Investigation of a number of cases has shown that this trouble is due to several factors acting in conjunction:— 1. The presence of an abnormal proportion of sulphates in the brickwork. 2. The presence of a high moisture content in the brickwork due to: — (a) Water absorbed during building operations, as, for instance, when work is carried out in inclement weather. (b) Absorption of water after erection due to certain features in design. (c) Absorption of water due to Jack of damp-proof course. 3. The use of unsuitable mixes for the rendering, in particular strong, dense materials with heavily trowelled finishes. ' The fact that these failures are more common in buildings finished with parapets, cornices, and similar features, without eaves projection is a matter for apprehension at the present time, since the so-called “ modern ” type of building is becoming increasingly popular. Finally, the composition and method of application of the rendering must be considered. Modern developments in various European countries and experimental work at the Building Research Station indicate that porous, open-textured finishes are to be preferred to dense, heavily trowelled work in strong mixes. Direct evidences of the relative vulnerability of porous and dense mixes to sulphate attack is not yet available, but for finishing coats at any rate there is every reason to adopt the weaker mix. NEW PHASES IN CONSTRUCTION Coloured footpaths are being constructed in some streets in New Orleans, U.S.A. The material specified is an aggregate made of chipped rocks, and is laid in a diamond formation, the shape being ensured by brass stripping. The surfaces are smoothed down with sand. An entirely new form of construction —windowless factory premises—are making their appearance in certain industrial centres abroad. Changes of light and atmosphere indoors will not be noticed by workers in these scientifically air-conditioned structures. They are being provided, moreover, with electric systems which will indicate to workers the kind of weather they may expect when leaving the building. One new type of factory is an almost square mass of three stories built of limestone, with a flat roof of concrete, which is dead level, and covered at all times with several inches of water, that acts as an insulator, A VERY WET TIMBER. Green timber may be amazingly wet. The moisture content of green timber is usually considered to vary from 40 per cent, to twice the weight of the solid matter in the timber. These figures arc based on the oven-dry weight of wood. Recently a timber with a green moisture content of between four and five times the weight of the wood itself was found in Southern Queensland. It is known botanically as laportea photeuiphylln. It is sometimes known as fibre wood. It has little commercial value, but when seasoned may be suitable for the purposes of insulation on account of its low density. LOAD CAPACITIES OF GLASS. Bending strength tests on strips cut from sheet glass demonstrated that conditions at the edges exercised an important influence. Glass strips, the edges of which had been entirely sealed and rounded off by fire-finishing, showed distinctly higher strengths than strips cut with a diamond or ground and polished edges. It was also found that the wider the strip the less was its relative strength, and that the fractures in narrow strips were not as complicated as in wide sheets. It would thus appear that a framework of very narrow strips of glass should carry heavier loads than a single sheet of the i same area. i