Methods of Waterproofing

The waterproofing capacity of the compound is indicated in the fact that two gallons mixed in cement will provide a coating one inch thick over a surface of 200 to 250 square feet; in mass work, the same quantity will waterproof one to one and one-half cubic yards; and used as a wash, two gallons will cover 500 square feet of surface, two coats.

Hydrated Lime.

This substance—placed on the market under a variety of trade names, such as Crown Hydrate, Tiger Brand White Rock Finish, etc.—consists of a very high grade of calcium oxide, almost 100 per cent chemically pure. It is mixed dry with the cement and ag gregates, before the addition of the water. While the amount to be used should vary some what with the character of the work required, an admixture of 10 to 25 per cent by weight of hydrated lime to the amount of the cement used will greatly increase the water-tightness of the concrete and make a rich mixture practically waterproof. The action of the lime seems to depend largely on the fact of its extreme fine ness, which, it is claimed, exceeds that of the finest ground Portland cement, and renders it capable of filling smaller voids, thereby increas ing the density of the mixture. It increases the plasticity of mortar and concrete, and their ease of working under the trowel, thus adding to the capacity of workmen in laying brick, blocks, stone, etc. It also greatly increases the adhesive power of mortar, the lime retaining moisture longer than cement alone, thus retarding the set and enabling the mortar to penetrate deeper and gain a stronger grip.

In a paper read before the 1908 annual meet ing of the American Society for Testing Mate rials, and based on a number of careful tests, Sanford E. Thompson announced his conclusions regarding the effect of hydrated lime upon the permeability of concrete to which it is added, as follows: 1. Hydrated lime increases the water-tight ness of concrete.

2. Effective proportions of hydrated lime for water-tight concrete were found to be as follows: One part Portland cement ; 2 parts sand ; 4 parts stone ; add 8 per cent hydrated lime.

One part Portland cement ; parts sand; 4% parts stone ; add 12 per cent hydrated lime.

One part Portland cement; 3 parts sand ; 5 parts stone ; add 16 per cent hydrated lime.

These percentages are based on the weight of dry hydrated lime to the weight of dry Portland cement.

3. The cost of large waterproof concrete structures may be frequently reduced by em ploying leaner proportions of concrete with hydrated lime admixtures; and small structures, such as tanks, may be made more water-tight.

4. Lime paste made from a given weight of hydrated lime occupies about times the bulk of paste made from the same weight of Port land cement, and is, therefore, very efficient and void-filling.

Hydrated lime will not swell or expand in concrete as will ordinary free lime. The swell ing of free lime in concrete after the work has set and hardened, sets up internal stresses which may cause the work to crack and peel off the surface, and may also give rise to blow-holes. These undesirable results, it is claimed, are avoided by the use of hydrated lime.

Many of the advantages claimed for this ma terial are based on considerations of economy. The addition of a small proportion of hydrated lime will greatly increase the amount of work that can be done with a certain weight of cement.

The quantity of lime that can be added to a mortar depends entirely upon the amount of Portland cement that is present in the mixture. The best results seem to be attained when the proportion of cement to lime is as 1 to 1, although proportions ranging from 1 to up to 1 to 2 have been used. The mortar made from one part Portland cement combined with six parts and and one of lime paste, seems to give the best results. The sand-carrying power of the cement is almost doubled by this mixture; and the mortar is easy to work, of great strength, hardening rapidly in air, and offering a perfect resistance to the weather.

Hydratite.

This compound also comes in powder form, and is first mixed dry with ce ment. Damp sand in the proper proportions is then mixed in, after which water is added to give the required consistency. Under average conditions, the quantity of hydratite needed is two per cent of the weight of the Portland ce ment used, or eight pounds to the barrel. The area which one barrel of Portland cement in various mixtures will cover with coatings of varying thickness, is shown as follows: The effects secured by the use of hydratite, it is said, are due to its chemical action upon the constituents of the body into which it enters. By this chemical activity it becomes an integral part of the mass, and the water-resisting prop erty it gives is claimed to be permanent. It increases the sand-carrying capacity of cement, and is said to have no deleterious effect on the strength of the concrete or its final setting. Its tendency is to make the concrete several shades lighter than it would otherwise be. A wide range of usefulness is claimed for it by its pro prietors—in reinforced work, stucco, walls (ap plied on interior side), floors (applied in top dressing), reservoirs, tanks, cisterns, silos, etc.