1932-06-18 — Page 2

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HONG KONG DAILY PRESS, SATURDAY, JUNE 18, 1932.

ENGINEERING AND BUILDING

BUILDING STONES

SOME NOTES ON CAUSES 'AND PREVENTION OF DECAY.

BUILDING RESEARCH BOARD AND ACTION OF THE ATMOSPHERE.

A special report on the weather-continuous cycle of change, ing of natural building stones, ench geological formation is the issued by the Building Research result of the consolidation of dia Board (H.M. Stationery: Offico., 4. Í integrated older rocks. Stone in Gd.net) forms a collected survey buildings in subject to the same of the seattered information avail- į agencies, and in addition " Ita able on the subject, and links up liability to dechy may be increased the results of investigations that have beon, carried out by the Build ing Research station during the past five or six years. It is offer ed as a fair and accurate state-

by atmospheric pollution, mistakes in the handling of the material, and the use of unsuitable methods for cleaning or restoration.

Among the natural inherent de ment of present knowledge, thoughfects of building stones which be further investigation may nodes- eome apparent after the material sitats" modifiëntion of the views ex-

has been exposed in a building is pressed..

the occurrence of hard and soft Containing 149 pages" the report, beds in the same stone, leading to "differential weathering," which often could not be anticipated from the original appearance of the

which is the work Mr. R, J. Schaf-

rain, or it may be carried. in solu

Forces set up the differences in

formed which differs in physical

the thermal expansion of the rock-properties from the underlying material, so that dangerous stresses farming minerals play a part in

are liable to be set up and ultimate- promoting decay. Cracks develop the skin muy fake off. Another ed in the surface of the materials

source of danger is that certain by these forces may become centres forme of trentment introduco of attack by the other weathering soluble salts as by-products of tho

apparent.

its way into sach a stong. Calcium sulphate may be carried from the limestone by direct washing by agents. For example, Cleopatra's renotions involved, and thero aults

Needle withstood for many con-may be extremely deleterious.

For now buildings, and modern tion in the pores and may tend to turies the daily temperature changes

of Egypt, but soon after its buildings, in which the stow is in accumulate in the sandstone by

condition, virtue of differences in the physical moval to London a marked decomparatives good properties of the two materials. Interioration in its condition became washing with water at regular in- selecting a material for # new

tervals is a cheap and effective building or for repairs to an old Frost is another physical agent moans of keeping stonework clean one it is therefore not sufficient to which induces decity. The offects and of retarding decay, even under determine that it has properties of its action are thought to have the conditions prevailing in densely which favour its use in a particular been exaggerated in England, as populated districts. Washing re- locality, but the possible effect of in spits of the climate stones are moves the salts which are largely and, the materials "with which it is to seldom sufficiently saturated by responsible for decay, wherons pru. be associated must also be given rnin to be badly damaged by frost,servatives tend to seal them within

enreful ocnsideration.

though in unprotected parapets and the pores, and it also eliminates cornicos, where a thorough soaking deposits of soot, which have the AGENTS OF DECAY.

by rain may occur, freezing may effect of false shadows, and which Pollution of the atmosphere by cause disintegration of certain it in erroneous to suppose form a acid gases is the main cause of the types of building stone.

protection to the, stonework. The decay of building materials that Living organiams vontribute in lenst eestly way of carrying out the contain calcium carbonate. Pollu- some degree to the decay of stone. washing operation is to

use fire- tion by solid products of combus- Whether there are bacteria which hoses from the ground level. In tion is also important, because scot can live in the stone and destroy many cases the pressure from the deposits cause disfiguration and it is a matter of controversy, but mains is adequate, though for high also because 3000 carries with it in some instances the presence of buildings a smail pumping engine acid materials which it brings into some, types of lichens is thought may be required. An annual wash The to be detrimental. In others, how-by hosing may normally be regard close contact with the Rone.

ever, lichens cause, no apparant | ed as sufficient, but more frequent principal neid products of the com- bustion of coal are carbon-dioxide harm, and it is stated that blocks application may be an advantage

of stone quarried at the time of for such parts us balconies, balus-' and sulphur dioxide. The effect on building "stones of the presence of the erection of St. Paul's and left trades, and predimenta. Too fre the former in the atmosphere is lying in the Isle of Portland for 160 quent washing of Portland atone defeot considered to be of relatively little years still showed the tool marks is, however, to be avoided, as it stone unheerseurily consequence, and the heid sulphur below the lehen growths. Ivy is makes the gnees are much more important. a serious menace to ancient stone whits and unduly roughans the aur- ed with natural defects inherent quences is the presence of minute

face. Whore stone can be scrub in the material, faulty craftsman-figures, which are termed "vents" Their main chemical action is the work.

conversion of the carbonates of when they are of weakness

bed by hand, as was recently done ship, and errors in the choice of

hy the Office of Works nt Bucking- effect of vents on durability largely calcium and magnesium into tho stone, with atmospheric pollution depends on the architectural style corresponding sulphates, and The report holds out histle hope ham Palace. washing every five in relation to wrathering, with the chemical and physical phenomena of the building, dangerous condi- calcareous materials it causes the of the discovery of a satisfactory years or so will probably prove ade

application to quate to maintain a good appear- associated with weathering, with tion of the Anston stone in the formation of hard impermeable au- preservative for

The results obtained ando in London. The public monu-, clable units and living organas House of Parliament is due to the face skins, which tend to blister stonework. as ngents of deeny, with preventive and remedial measures, and with use of a vented stone for a highly and exfohate thus causing the de- with such materials have been diamanta maintained by the Office of Works are now regularly washed the testing of building materials in decorated building, and it is prin-velopment of an ugly type of decay.appointing, and the Building Ro

with water. relation to the estimation of theicipally in, the decorative and free. Limestones also suffer a breakdown search Station is at present unable durability. The text is accom-

Regular washing can be effective panied by over 50 half-tone illu-standing features that restoration of their internal structure. Some to recommend the use of stone pro-

In the times this takes the form of a pow-suriktive solutions except to pro in keeping stonework clean only ¿f his become necessary,

temporary protection in begun in time. If it is desired to Muscum of Practical Geology in dering of the stone immediately vide

The pro-clean a "blackened frontage the Jermyn-street, which was built of behind the skin, probably due to special circumstances. Anston stone, at about the same the retention of liquids which are perties demanded of a perfect storm-brush process can be used

unable to time as the Houses of Parliament, because of the denseness of the

cscape by evaporation stone preservative are, it is point with advantage. The report, how-

ધર્મ out, many and conflicting. ever, emphasizes that the use of the opening of the vents has had skin sometimes a series of crucks

Thus a waterproof agent is requir- alkalis, whether in conjunction with no serious consequences because the occurs parallel to the exponedosar

ed to prevent penetration of mois steam or without, should never be building is in "Classic style with face; nometimes the internal strile- ture is shattered. Structural fon-

ture, but at the same time shouldepuntenanced, since it is definitely plain wall surfaces and few pro-tures probably determine the degree jecting overhanging features of attack by neid gases and the permit the escape of water which harmful, though apparently bene- degree of resistance to the effects has gained access at some unproficial, in that the building appears of the crystallization of salt tected point. A common cause of

cleaner.

Attempts to eliminate the The texture of the stone alau нeems to influence the thickness of the failure is that even in porous mate-alkali by subsequent washing with akin, and the strength elasticity, riala and under the most favour

a weak acid such as, vinegar ara which are also related to structure, nhle conditions, the preservative unlikely to be effective, and dan- are likely to have considerable in ferce in detemining the liability

penetrates only to a relatively perous suluble salts are still habe of a stone to exfoliation,

small depth, and a surface skin is to remain.

fer, deals in n dozen chapters and two appendices with the classi fication of the naturaleatones used for building purposes with dif- ferent types of weathering associat

strations.

"NATURAL DEFECTS.

No one, it is pointed out. resists the, action of atmospherie agencies indefinitely. In Nature the surface of the earth suffers a

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ERRORS OF CRAFTSMAN- SHIP,

Damage to stonework may arise from iron cramps and dowels, the use of which may be regarded as an error of craftsmanship which haa" persisted although the pos- sibility of damage resulting from it was known as early as the 5- teenth century. Wren Was well aware of the danger of using iron in buildings wherever oxidation occur, and is said to have specified that no iron should be used within Din of the air. It is clear, how- ever, that his instructions were not In St. carried out by his builders. Paul's over 1,000 iron cramps and dowels were removed from the main pers during the recent repairs," and many of them, which had caused much damage to the masonry, were within an inch or two of the surface of the stone. In one ease the iron was found to be completely encased in copper,, and no corrosion had occurred. Further damage has resulted from the later introduction of iron reinforcements, some of whicir, it is believed, were inserted during Wren's lifetime; in sorae of these the iron was merely faced with lead and painted to match the colour of the stone.

It has not hitherto, been ade-. quately recognized that an incum-

LIGHTING & POWER INSTALLATION patibility exists between certain

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types-of-building-stone--The-1880- ciation of a limestone with a sand- stone, for example, frequently re- sults in the rapid decay of the latter. The deleterious, action may 'show itself even with those sand- stones which when used alone hæve" extremely good weathering quali- tice. Sandstones in which tho grains are not cemented by siliceous material are not liable to direct at. tack by atmospheric sulphur gases, but excessive decay may result if 'calcium sulphate resulting from the decomposition of a limestone finds

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