117. Asphalt Waterproofing. If asphalt is to be applied to a concrete surface, the concrete should be dry; and it will be found generally more satisfactory to coat the dry surface first with asphalt cut with naphtha. Unless the concrete is heated, it is generally very hard to make the asphalt adhere to the concrete. Hot asphalt applied to ordinary concrete surfaces will generally roll up like a blanket when it cools. The concrete should be heated by hot sand, or the asphalt should be cut with naphtha. 'When the coat con taining the naphtha has been applied—like a coat of paint—and is dry, then the asphalt mastic is applied. The asphalt mastic is com posed of 1 part asphalt to 4 parts of sand. This is smoothed off with hot irons, and thoroughly tamped into place. If stone or earth is to be placed next to the asphaltic surface, it is best to cover the sur face with roofing gravel to protect the asphalt.
Asphalt paint has been used for a protective coat for all kinds of masonry where earth is to be placed against it.
A coat of asphalt + inch thick applied with mops to a grout surface, has been used satisfactorily for coating the interiors of tanks, for heads greater than 19 feet, by Mr. J. IV. Schaub ("Transactions" of the American Society of Civil Engineers, Vol. LI). Mr. Schaub states that he believes the I-inch coat, in addition to the grout, is sufficient for a water pressure of GO feet.
11S. Felt Laid with Asphalt. In waterproofing floors, roofs, subways, tunnels, etc., alternate layers of paper or felt are laid with asphalt, bitumen, or tar. These materials range from ordinary tar paper laid with coal-tar pitch, to asbestos or asphalt felt laid in asphalt. Coal-tar products deteriorate when exposed to moisture. Some asphalts are more suitable than others for waterproofing pur poses; therefore the properties of any asphalt intended for water proofing should be thoroughly investigated.
In using these materials for rendering concrete water-tight, usually a layer of concrete or brick is first laid. On this is mopped a layer of hot asphalt; felt or paper is then laid on the asphalt, the latter being lapped from 6 to 12 inches. After the first layer of felt is placed, it is mopped over with hot asphalt compound, and another layer of felt or paper is laid, the operation being repeated until the desired thickness is secured, which is usually from 2 to 10 layers—or, in other words, the waterproofing varies from 2-ply to 10-ply. A waterproofing course of this kind, or a course as described in the paragraph on asphalt waterproofing, forms a di tinct joint, and the strength in bending of the concrete on the two sides of the layer must be considered independently.
When asphalt, or asphalt laid with felt paper, is used for water proofing the interiors of the walls of tanks, a 4-inch course of brick is required to protect and hold in place the waterproofing materials. Fig. 11 shows a wall section of a reservoir (Engineering Record, Sept. 21, 1907) constructed for the New York, New Haven & Hartford Railroad, which illustrates the methods described above. The waterproofing materials for this reservoir consist of 4-ply "Hydrex" felt, and "Hydrex" compound was used to cement the layers together.
Fig. 12 is an illustration of the method used by the Barrett Manufacturing Company in applying their 5-ply coal-tar pitch and felt roofing material, and it shows in a general way the method of laying asphalt and felt for waterproofing purposes. The company's
instructions for applying this roofing are as follows: "First coat the concrete (A) with hot pitch (B) mopped on uniformly.
Over the above coating of pitch, Jay two thicknesses of tarred felt (C), lapping each sheet seventeen (17) inches over the preceding one, and mopping back with pitch (D) the full width of each lap.
"Over the felt thus laid, spread a uniform coating of pitch (F) mopped on. Then lay three (3) full thick nesses of tarred felt (F), lapping each sheet twenty-two (22) inches over the preceding one.
"When the felt is thus laid, mop back with pitch (G) the full width of twenty-two (22) inches under each lap. Then spread over the en tire surface of the roof a uniform coating of pitch, into which, while hot, imbed slag or gravel (H)." In applying asphalt and felt for general waterproofing pur poses, the felt, as already stated, would be in a continuous roll, and not in sheets as shown for roofing purposes.
119. Medusa Waterproof Compound. Among the many patented waterproofing materials on the market is the "Medusa." This compound is claimed to prevent efflorescence, as well as to make concrete waterproof. In using it, the following directions, given by the manufacturing com pany, are to be observed : "To render cement work impervious to water, a small quantity of the compound is thoroughly mixed with the dry cement, before the addition of sand and water. For most purposes, from 1 to 2 per cent of the weight of cement used will be found sufficient. This is equivalent to from four to eight pounds of the compound to one barrel of cement. The precise amount to be used mist be left to the experience of the user, and depends upon the proportion of sand, etc., employed, and on the kind of work to be done Our own experience has been that the use of 1 per eent--1 pounds to the barrel, or 1 pound to the sack of cement—is enough to make hollow concrete building blocks water-tiglit. For cistern and reservoir linings and other work which must he absolutely impervious, a somewhat larger amount should be used. Thorough mixing is of the utmost importance." In the operation of waterproofing, a very common mistake is made in applying the waterproofing materials on the wrong side of the wall to be made water-tight. That is, if water finds its way through a cellar wall, it is generally useless to apply a waterproofing coat on the inside surface of the wall, as the pressure of the water will push it off. If, however, there is no great pressure behind it, a waterproofing coat applied on the inside of the wall is usually suc cessful in keeping moisture out of the ,cellar. To be successful in waterproofing a cellar wall, the waterproofing material should he applied on the outside surface of the wall; and if properly applied, the wall, as well as the cellar, will be entirely free of water.
In tank or reservoir construction, the conditions are different, in that it is desired to prevent the escape of water. In these cases, therefore, the waterproofing is applied on the inside surface, and is supported by the materials used in constructing the tank or reservoir. The structure should always be designed so that it can be properly waterproofed, and no asphaltic waterproofing should be laid at a temperature below 25° F.
The above-described methods of waterproofing are applicable to stone and brick masonry as well as to concrete.