The author of this article, W.H. RANSOM of the BUILDING RESEARCH STATION IN ENGLAND, describes the taxing conditions which building materials must stand up to in the tropics.
He takes a selection of characteristic new products: polyethylene, pvc, translucent corrugated roof sheets, polystyrene, wood particle board, paper resin laminates, pva emulsions and pitchfibre — and states in what conditions each can be used.
TROPICAL
15.5
UILDING materials will, initially,
possess certain desirable proper- ties. They may
be strong and resistant to impact and fire; they may be elastic and have the ability to adhere to other materials; they
be waterproof and of good appearance. When exposed to the weather under normal working con- ditions these initial properties can change. Then the material may cor- rode and become weaker; it may embrittle, fade and discolour. Ob- viously it is an advantage if the probability of such changes can be forecast. In the Tropics, however, many of the materials to be described are very new and there are few relevant laboratory results specific to the climatic conditions.
SO
some
now
Even
useful guidance on probable behaviour can
be given though some of the remarks made in this article will, no doubt, need to be modified in the light of future practical experience.
cause
The factors that
detrimental changes in a material are often present in both tropical and temperate areas.
It is primarily the variation in the degree of intensity of these factors which is responsible for any differences in behaviour in the two climatic regions. The essential difference lies in the much higher levels of solar radiation--both light and heat-received in the Tropics.
Because of absorption by cload and dust, solar radiation received at the earth's surface is a maximum, not at the Equator, but between latitudes of 15 and 35 degrees both north and south of the Equator. (The world's highest shade air temperature of 136 deg. F. was recorded at Azizia on latitude 32 degrees N.)
The surface temperatures attained by building materials by day are greater than the corresponding shade air tem- perature. Then a duli or black surface, especially if insulated underneath, may well be some 50-60 deg. F. hotter. Moreover, at night it can fall below air temperature when the atmosphere is clear with little moisture or dust.
High temperatures in themselves can cause fundainental changes within ma-
32
BUILDING CON OWN PROBLEMS
terials particularly in the organic materials, bitumen, paint, plastics and changes which are manifested
rubber
by embrittlement.
Volatile constituents-e.g. paint driers -will be lost more rapidly and prema- ture evaporation of water from cementi- tious mixes will result in poor hydration and hardening. Furthermore, high tem- peratures have the secondary effect of stimulating biological activity and in- creasing the rate of other degradation reactions both of which are detrimental to many organic materials.
cause
Fluctuations in temperature thermal movements of materials. These impose differential stresses upon different materials used in conjunction with one another and even within a homogeneous material through unequal heating of the surface and underlying layers.
These
stresses can
cause crazing, cracking and distortion. This is most marked when changes are large and rapid for example, in hot, desert areas where diurnal temperature variations are high. In equatorial rainforest areas changes are much smaller and may well be less than in temperate regions. Quite apart from any heating effects. the shorter wavelengths of sunlight itself can be absorbed by bitumen, many paints, plastics and rubber. Embrittle- ment, crazing and discoloration are caused, the effects being most pro- nounced at high altitudes and in coastal
areas.
Moisture is detrimental to most building materials. Deterioration is most likely in equatorial rainforest areas where humidities are so high that the small drop in surface temperature of a material at night frequently results in heavy condensation upon it. Even when stored under cover building materials can then be thoroughly wet- ted. They may corrode or rot particu- larly when condensation occurs in rela- tively inaccessible crevices from which subsequent evaporation is slow.
are
Prolonged high humidities, too, conducive to mould and algal growth. At the best, building surfaces are disfigured; at the worst, decay can result. Tropical savanna regions have markedly wet and dry seasons and the annual range of relative humidity can exceed 90 per cent; the daily range can be greater than 70 per cent.
Such extreme fluctuations of humidity cause marked dimensional changes of
many building materials-notably of timber, boards, earth, and cement pro- ducts. Warping, splitting, crazing and cracking can result.
Rainfall amounts in tropical areas vary widely but in general terms the wettest areas may be said to be between 10 deg. N. and 10 deg. S. Here annual totals commonly exceed 60 in. and may exceed 100 in. High intensity falls of 2-3 in. per hour are not uncommon during storms.
High total rainfall and high intensity falls keep humidities high, cause the prolonged and thorough wetting of materials, and can erode the softer ones, Tropical convective hailstorms can be severe and even material such as con- crete and clay tiles, asbestos-cement and thin gauge aluminium sheets can be broken by hailstones which at times weigh over 1 lb. Paint films, too, can be damaged.
Damage by insects to building ma- terials is chiefly caused by the termites, whether earth-dwelling--where contact with the ground is vital to their life- or wood-dwelling-where no such con- tact is needed.
Both types feed on timber, fibreboard, hardboard, and some plastics and can damage bitumen, paint, rubber and earth in their search for food. Termites are widespread and cause much damage where remedial measures are not taken.
Damage through atmospheric pollu- tion is generally less in the Tropics than in the more industrialized tem- perate areas, but in hot, desert areas wind-blown grit can etch glass and erode paint films.
Near surf beaches, too, the high concentration of sea-salt in the atmos- phere degrades paint films and promotes the corrosion of metals.
Plastics figure prominently amongst the building materials most recently introduced into the Tropics. Of the many types now available special men- tion must be made of polyethylene, polyvinyl chloride (pvc), acrylic resins, polyester resins and polystyrene.
are
Polyethylene, stabilized with carbon black, has been used indoors for above- ground cold water service pipes, At normal indoor temperatures these tough with a high impact resistance. They do not corrode and present-day compression jointing and welding tech- niques have overcome earlier fixing difficulties. They should not be used
THE HONG KONG & FAR EAST BUILDER · VOLUME 15, NUMBER 6