is then obtained by a granolithic finish, put on with a steel trowel or wooden float. When tiles, bricks, or slates are used over a water-proofing membrane, they are laid on a thin mortar-bed, the joints grouted with cement mortar, and expansion-joints provided as described in the case of concrete slabs. In this connection it should be noted that if the work is done in cold weather the join's should be only half filled with mastic, as otherwise the expansion in the summer will force the material over the top of the joint and cause an unsightly appearance. (Fig. 4.)

PREPARED ROOFINGS AND READY ROOFINGS are seldom used except on temporary wooden roofs or for small areas of steeply pitched concrete roofs, as they are usually inferior to those of the membrane-type.

Tile is a satisfactory roof-covering, widely used for pitched ROOFS OF INDUSTRIAL BUILDINGS. Interlocking cement tiles as well as both long-span and short-span gypsum tiles, applied directly on the steel roof-framing, are employed. Cement tiles can be obtained in lengths up to 10 ft and of various thicknesses. Flat cement tiles, in lengths up to 6 ft, weigh from 14 to 18 lb per sq ft. The gypsum tiles are made in 12-in and 18-in widths and in different

If Poured in Winter

If Poured in Summer

-Concrete Wearing-Surface
Built-Up Roofing

-Structural Slab

Fig. 4. Expansion-Joints in Concrete Wearing Surface

lengths up to 8 ft. For the same span the weight is about equal to that of the concrete tiles, but the thickness is approximately double. Terra-cotta roofingtiles, also, such as are used for residential work, are suitable for industrial buildings with pitched roofs when their cost is justified. The use of either terra-cotta, tile or slate, however, requires a roof-deck of wood or of some material like "nale-code" into which nails can be driven. If NAILING-STRIPS are to be left in the concrete they should be 1 by 2 in in size, and so placed that the compressive resistance of the slab is not materially affected. Before applying either tile or slate the roof should be covered with one thickness of roofing-felt, properly lapped and nailed on with capped roofing-nails.

4. Flashing. Wherever the roofing abuts against a vertical surface, such as the face of a chimney or a parapet-wall, it is necessary to employ some form of flashing. The materials generally used for this purpose are 16 oz soft rolled copper, No. 22 gauge galvanized iron, or some form of plastic compound. On one-story buildings, and where parapet walls are not required, gravel stops are used on flat roofs covered with slag or gravel (Fig. 5). When a roofing with asphalt as a cementing material is used, it is carried over the edge of the roof and nailed to wooden blocks embedded in the concrete slab. (Fig. 6.) If the roof slopes toward the outside walls of the building, gutters and leaders are provided,

for the straps of which nailing-blocks should be placed in the structural work. The ordinary method of flashing employed on flat roofs with a membrane covering, is to place the base-flashing on top of the upper ply of the built-up roofing at the time of laying, and then to place two or three additional strips of felt on top of the metal, the whole being thoroughly mopped with pitch. Fig. 7 shows a detail recommended for a brick parapet wall, in which the width of the wall,

up to the cornice on which the flashing is placed, is 1⁄2 in less than it is above that level, in order to prevent the water running down the inside face of the parapet from getting back of the flashing. Fig. 8 illustrates the same type of flashing when used for concrete walls. In order to hold the cap-flashing in place against the inside of the wall-form during the operation of pouring the concrete, wooden blocks % × 14 × 6 in are spaced 2 ft on centers as shown in Fig. 9.

Fig. 10 illustrates a method of flashing which has been successfully used under

Fig. 7. Cap and Base-Flashing for Brick Walls
Fig. 8. Cap and Base-Flashing for Concrete Walls

varying conditions, and which includes the use of a diagonally sawed 2 by 4 in wooden strip to form the recess. Before placing them in the forms the two wedge-shaped sections are lightly nailed together in such a manner that the strip on the face of the finished wall can be removed without difficulty after the concrete has hardened, leaving the desired recess. The other strip, which is designed to serve as a nailing-ground for the cap-flashing, is anchored into the concrete. Nails driven through the forms are used to hold both strips in place while the

concrete is poured, and must be withdrawn before removing the forms as otherwise the edge of the recess or chace is likely to be broken off when the forms are taken down.

Besides the standard metal flashings there are a number of proprietary

Fig. 9. Metal Base-Flashing and Felt Base-Flashing for Concrete Walls
Fig. 10. Special Type of Flashing at Concrete Parapet Walls

materials such as the Flex-Lock Flashing for brick walls made by the Barrett Manufacturing Company (Fig. 11). This firm supplies, also, a special FLASHING-BLOCK (Fig. 12), for use in brick walls and a FLASHING-FORM, designed for concrete walls (Fig. 13).

Fig. 14 illustrates a satisfactory method of waterproofing about the base of structural steel members that rest upon a concrete roof. In this case it is necessary to construct a PITCH-POCKET formed of a hollow, copper box filled with pitch.

Fig. 14. Waterproofing at Base of Structural-Steel Member

A METAL FLASHING is the most satisfactory kind for a pipe passing through a concrete roof-slab, and Fig. 15 shows three types that have been successfully used employing this method. For steam-pipes the hood-cap type as shown in Fig. 15(a), should be used in order to allow for expansion and contraction and

prevent the breaking of the joint between the metal flashing and the roofmembrane.

The types of flashing to be employed for SKYLIGHT-CURBS, MONITORS, ETC., necessarily vary with the conditions, but it is customary to carry the flashing up the face of the curb and to attach it on top by means of a wooden nailing-strip embedded in the concrete. Figs. 16 and 17 show two satisfactory methods of flashing used for skylight-curbs, monitors, ventilators and scuttle-covers.

Fig. 18 illustrates the ordinary method of flashing around a brick chimney. For steel stacks flashing of the hood-cap type, as shown in Fig. 15(a), is used. It is attached to the stack by means of a metal collar as in the case of steam pipes, Fig. 15(a).

5. Methods of Basement-Waterproofing. The problem of providing adequate protection against the infiltration of ground-water is one which should

receive careful consideration in the earliest stages of the design. At that time accurate information should be obtained from the site as to the hydrostatic head to be resisted and a decision made in regard to the choice of methods to be used, as this may determine the details of the substructure of the building. The methods ordinarily employed for waterproofing the basements of buildings may be divided into four general classes, INTEGRAL, SURFACE COATING, MASTIC, and MEMBRANE.

6. The Integral Method of Waterproofing Basements. The function of an INTEGRAL WATERPROOFING MATERIAL, which is mixed with the concrete either in the form of a liquid, paste, or powder, is to make the concrete itself more impermeable, either by filling the voids with an inert material, or by increasing the activity of the cement through the addition of liquid chemicals. They also act to a certain extent as lubricants for the aggregates and tests apparently show that the use of small proportions of powdered admixtures do not