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• The Treatment Of
BEFORE comparing the yariods' Methods of water-proofing the outside Of a wall, it will be well for us to-examine some other ways by which damp can Make an 'entrance, since any general treatment is not only: unnecessary but useless if
the real source of the trouble is Seine unperceiYed local Chink . . in the defences.' =
Only prohibitively-' expensive .bricks can claim' tfl he impervious to waier;, but, except in yew unfityourable circumstances, any. good quality brick should be able to evaporate moisture .before this has had thug to soak through. It is important to' know what circumstances. May fairly rank as unfavourable. In the first place, no Inick.shotild..be exposed to a steady.stream of water such as may leak fiom a choked gutter or down-pipe--or eVen-froiri a wide sill. It shindd not be exposed to drippings from heavy trees, especially if these retard evaporation by screening off the Sun and Wind:• (hut I would point out that tlietelief commonly held that ivy inakeett wall damp is fallacious : on the contrary, the disposition of the leaves is extremely effective in keeping every drop of rain off the wall—as an examination of its surface after a heavy shower will prove. But if the wall is damp for any other reason the ivy will, of course, - tend to prevent it drying. Deciduous creepers cannot be held so innocuous after they have shed their leaves.) Lastly, a brick is not intended to present a horizontal surface on which water can lie and soak downwards. In this connexion one must condemn the common practice of building "party walls" with a finishing course of bricks laid on edge. - The fatuous device-of providing a clear eighteen inches of wall above the tiles on the boundary of any two properties was recommended as a protection ' against fire in the "Model By-laws of the Local Government Board," and has been adopted in many districts. It is at least arguable that the damage by damp due to its inter- pretation must be vastly greater than that saved by its fire- preventive qualities. Certainly, a waterproof or sloping capping should be put on top, broad enough to throw the water dear of the brickwork below.
In the absence of any such obvious source as on uncapped wall or defective roof, suspicion will rest' first on gutters, down-pipes and lead flashing.. The simplest, though the least
pleasant way of examining these is a heavy shower-, of rain which may disclose -some obvious flaw that cannot ha detected at any other time. Suspect the presence of any mud, leaves or mass which could retain water and perhaps lead it (uphill as readily as down) to unprotected brickwork. Moisture will climb vertically for three or Di& inches at least up any really dirty surface. Lead is liable to have Perished if it has been anywhere in contact with lime mortar ; zinc is badly corroded by the air of towns ; cement- may have cracked or come away from the brickwork ; downpipes may be choked; or they "raityThe 'ciaekecl on the side nearest the house. A simple and permanent -cure for many of these minor flaWS is to apply one of the 'several plastic compositions, such as " Tilo," which will stickto any surface that is free from dust. ■. • A chimney often provides an entrance for damp. Suspeet all round the base where it runs into the roof, and, in particuldr, any "set-backs," where the courses of bricks are stepped, leaving exposed Arrizontal -surfaces -.All -thes-should-be carefully weathered with cement mortar set at a sharp angle. Lime mortar is useless for the purpose. A similar trouble can arise inside a chimney and is easily recognized by the characteristic dark brown stains which appear on the chimney-breast inside. The flue is bent to improve the draught and to keep the rain off the fire, as also to accommodate other flues in the chimney ; but if a careless bricklayer has omitted to weather all surfaces on which soot could otherwise lodge, this may become saturated with rain, which will then soak through into the room. A radical cure for this is troublesome and expensive, involving cutting out the brickwork, weathering the flue and making good—and, unless the patch is very large, it can generally be treated in a more superficial way.
Windows may let water in between frame and sill, or between Sill and wall. In the former case, the joint should be well raked out all round and repointed with mastic. (cement is of no use, since the different expansions of wood, metal, and stone or brick call for an elastic joint). In the latter, the sill should be provided with a " throating groove" under the front edge, to prevent drips being blown back against the wall and its joint, too, raked and repointed—with mastic if it is a wooden sill, with cement if it is stone. Should a sill overhang less than two inches, it may be wise to build it out to this width, grooving it as before. An alternative is to fix a fillet across with an overhang below, so as to throw the drips clear. In cavity. walls, mortar dropped and allowed to remain on wall-ties and the tops of window or door-frames will form a bridge across which damp can travel to the inner walL The cure is to open the wall and remove the mortar.
We have now examined most sources of darripness and prescribed various local cures : it remains for us to discuss more general treatments. A wall whose dampness is due to porosity or to its exposed position can be successfully treated without altering its appearance by various patent colourless solutions ; but these lose their effect after three or four years and must be renewed. The only one I know which can be put on a wall while this is actually damp is " Neal's Waterproofing Compound " : the others must wait for a settled spell of dry 'weather. They are cheap and easily applied. A half-inch rendering of one part cement to two parts of clean sand (with the possible addition of a water-proofing compound such as " Pudlo ") is absolutely permanent if well done, but it is ugly. It should not be painted for at least a year unless it is first chemically neutralized. Cement wash is ugly and of little use. Boiled linseed oil is effective for several years, but it darkens the bricks and gives them a glossy look. Tar is perhaps the cheapest ; but it, tuo, is unsightly and needs renewing every five years. Various plastic compounds are made but they are usually black—as is asphalte, which needs expert application. Tiles laid on battens of wood will solve the problem in houses of a suitable type. They have the advantage over all other methods that they allow the moisture in the wall to dry outwards after they have been fixed.
No external 'treatment is of any use if the, damp-course is absent or faulty : in such cases the inside walls should be rendered with cement and finished with lime plaster to
avoid condensation, as in the first of these articles. Palliatives for inside use include pitch paper or Willesden paper, both of which, being organic, perish sooner or later, and tin-foil, which is permanent. These can be put on under the wall-paper—but since there is the possibility of the damp spreading beyond them, a wide margin should be allowed. The colourless compositions described for outside can be used, or a black emulsion called " Protex." For all these things the wall must first be dried, either with fires or the use of a blow-lamp ; and, since they are imporous, they encourage condensation in a cold room.
I come lastly to the most surprising of all—the " Ernapen " process. This has been adopted, after trial, on many important buildings on the Continent, such as the palaces at Versailles and Brussels, and may be considered reliable. It consists of a carefully calculated number of small porous tubes which are let into the external walls at a predetermined angle. Their effect is to evaporate automatically the moisture in the wall at the rate, in some eases, of several quarts a month for each tube. There must be many cases in which the" Knapen " process offers the simplest solution to the problems we have