Copper Flashings - A Manual - 1925 - Page 43
Notes on Copper Flashing Practice
KEEPING BUILDINGS DRY
An Article on the Flashing of Terra Cotta
By Cecil Fidler, Engineer of Standards, Atlantic Terra Cotta Co.
There is no doubt that in the past the importance of flashing in building construction has not been fully recognized. It has long been the custom to flash gutters and to use flashing at the junction of roofs and parapets, but it is only recently that designers and owners of buildings have begun to realize the necessity for flashing the entire upper and rear surfaces of exposed architectural features. It is now becoming evident that more attention must be paid to the protection of parapets and copings, the top of cornices and the floors of balconies.
An extensive examination of buildings erected in the last thirty years shows conclusively that the saturation of cornices and parapets is a very prevalent condition. In some cases the water enters at the mortar joints in the top of the coping. In other cases rain beats in and soaks in at the joints in the back of the parapet wall. Very frequently the mortar joints in the wash of the cornice are so cracked and porous that a lot of the water that runs down the parapet or falls on the top of the cornice finds its way into the interior of the wall.
Many architects and owners find that they have been placing too much reliance on the mortar joints. Having procured weatherproof building materials, such as terra cotta or hard stone, and having specified mortar of tested ingredients and approved mixture, they supposed that their buildings would be water-tight when erected. They are now finding that a great many buildings are not water-tight and on searching for the cause, they usually discover that the water is getting in at the mortar joints in the wash of the cornice and parapet coping.
At a first glance, it might appear that by carefully caulking or grouting the joints in the wash of cornices, parapets and balconies, it should not be very difficult to make them water-tight, but the present condition of a great many of these features proves that for one reason or another, water-tight joints are not being obtained. The bad condition of the mortar joints may be attributed to a variety of reasons, as for instance, poor workmanship, poor mortar, disintegration by frost, or cracking of joints due to thermal expansion and uneven settlement.
Many kinds of elastic cement and various caulking compounds for the protection of mortar joints are on the market and some of them remain impervious and somewhat elastic for several years but none of them appears to retain its original qualities indefinitely. Protection by means of caulking compounds involves periodical examination and considerable maintenance.
The results of poor joints are far reaching. The most common visible damage due to leaky joints in washes is unsightly staining and streaking on the face of the architecture. This staining and streaking is often extensive enough to destroy the beauty of a costly building. Frequently the streaks and discolorations clearly indicate that soluble portions of the mortar are seeping out at the beds and joints and are being deposited on the face of the building. Such a condition as this if allowed to continue will rapidly bring about the disintegration of portions of buildings on which it occurs.
Another serious result of leakage at joints is damage to plaster ceilings and walls within the building. Cases have been known where water entering at leaky joints in the washes of cornices and parapets has penetrated the walls to the depth of several stories below, causing considerable damage to the paint and plaster on the inside of the walls.
A still more serious condition, worse because it is out of sight, is the effect of dampness on steel framework within cornices, balconies and balustrades. The presence of moisture leads to rapid corrosion of the steel members and may eventually render projecting features unsafe.
Architects and owners of buildings have also to consider the damage that is caused by the freezing of water that collects in pockets and open spaces in the interior of walls and structural features. The expansion of ice repeated through a number of winters may finally rupture the masonry.
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