Fig. 25   Hollow Basement Wall.

Fig. 25 - Hollow Basement Wall.

A. lower stoneware ventilating .damp own, B. upper stoneware ventilating damp-course,. cc, bonding blocks.

Fig: 26.   Wall with Cavity filled with Artificial Asphalt.

Fig: 26. - Wall with Cavity filled with Artificial Asphalt.

For waterproofing walls in this way, some kind of artificial asphalt is usually employed. The mixture of pitch, oil, sand, etc., made by rule of thumb by the builder or one of his labourers, is far from reliable, unless very careful supervision be exercised. More satisfaction will be given by the use of one of the well-known compositions specially made for the purpose, such as the "Hygeian Rock" and "Tenax" compositions, and "Sub-aqueous Asphalt". Sometimes one of the natural asphalts, - Limmer, Seyssel, Ac, - is used.

One disadvantage of this method of construction is that the outer portion of the wall is not protected against the damp. In order that this portion may be as small as possible, the outer skin of the wall should be only a half-brick thick. A horizontal damp-course, extending over this outer skin, must always be laid a few inches above the surface of the external ground. A second disadvantage is that no inspection of the vertical damp-course is possible, and consequently defects - which may occur through carelessness, or the presence of small pieces of mortar or brick, or water - may not be discovered till damp has struck quite through the wall, perhaps some time after the house is occupied.

The only way of making the whole of a wall in wet ground quite dry is to spread a waterproof coat on the outside of the wall. For cottages and other buildings where economy is a paramount consideration, a very thin mixture of boiled pitch and oil may be applied to the wall with a brush, but this method has little to recommend it save its cheapness. The best method is to spread on the wall one or two layers of natural asphalt, carefully connected with the horizontal damp-course as shown in Fig. 27. In connecting horizontal and vertical damp-courses a triangular fillet is usually employed as at D. The top of the vertical asphalt may be finished by tucking it into a joint above the ground to the depth of about an inch, or may be connected with a second horizontal damp-course at that level. Where the exposure of the vertical coat of asphalt above the ground is objectionable, recourse may be had to the arrangement shown in Fig. 24, where the asphalt is faced outside with a 4-inch skin of brickwork.

Fig. 27. External Vertical Damp course of Natural Asphalt

Fig. 27.-External Vertical Damp-course of Natural Asphalt.

A, vertical asphalt damp-course; B. lower hort-zontal damp-coarse; c. upper horizontal damp-course: D. asphalt fillet; E. concrete foundation and ground-layer; r, concrete floor finished with terrazzo, and rounded to meet plinth; a, glazed brick plinth; h. glased brick capping to dado.

Before laying a vertical damp-course of natural asphalt, the wall should he dried by means of coke-fires and the joints raked out to the depth of an inch. The joints are then filled with mastic asphalt, and afterwards the proper layer is spread upon the wall. Sometimes a single layer inch thick is used, but in wet situations two ⅜ - inch layers are necessary.

It not unfrequently happens that a basement or cellar is required to extend below the permanent level of the ground-water, or below the flood-level of an adjacent river. It is then necessary to cover the ground-layer and walls with a sheet of asphalt absolutely flawless and continuous, and so arranged as to resist the pressure of the water. Fig. 27 exhibits a simple method of doing this; the horizontal coat is spread cither on a level concrete bed or when the walls have been built to the level of the ground-layer, and on it the upper walls arc built and a sufficient weight of concrete is deposited over the ground-layer to resist the upward pressure of the water. In exceptional places, where the pressure is great, the concrete ground - layer may be formed with a concave surface (as shown in Fig. 28), on which the asphalt is laid. An inverted arch of one or more 4i-inch rings of brickwork in cement-mortar may then be built on the asphalt and finished above with concrete; or the brick arch may be omitted and concrete alone be trusted to resist the upward stress.

In the case of cellars sunk below the permanent level of ground water and therefore below the drainage-level, the formation of an open area is obviously unwise, as no outlet can be obtained for the rain-water which may find its way into it. The best mode of construction in such cases is the solid wall asphalted outside, even though it be necessary to construct a temporary coffer-dam in order to keep out the water during the progress of the work. Only in the most exceptional circumstances, however, should cellars be constructed below the level of the ground-water. It is always more conducive to health to raise a housefloor well out of the ground, than to sink it below the ground, and it is usually cheaper.

Fig. 28   Asphalted Floor and Wall to resist considerable Pressure of Water.

Fig. 28 - Asphalted Floor and Wall to resist considerable Pressure of Water.

A. vertical asphalt damp-course; a, lower horizontal damp-course; C, concrete bed to receive asphalt; D. Inverted brick arch; E. concrete filling and floor.

Where ordinary open areas, dry areas, and cavity-walls are adopted, provision must always be made for ventilating and draining them; otherwise they will prove of little or no use.

The materials used in the walls of basements, especially in those walls which are in actual contact with the ground, are often of the commonest kind. Anything is good enough to be buried is the builder's thought. Certainly where an external asphalt layer is adopted, there is not so great a necessity for impervious and non-absorbent materials, but as a general rule it may be said that materials exposed to damp, as in basement walls, should be hard, dense, and durable. Soft porous bricks and coarse friable stone are out of place in such situations. The nature and properties of building-materials will be discussed a little more fully in the next chapter; suffice it now to say that the bricks should be hard and dense - blue Staffordshire bricks for the best work, - the stone close-grained, and the mortar of the best. It is a good plan to use hydraulic mortar in all basement walls, either Lias lime, or (tatter) Portland cement. Concrete coin-posed of Portland cement, sand, and hard, well-broken aggregate, mixed in proper proportions (1+2 + 3 or 4), is an excellent material.