Connecticut western news., 1911-08-24
WATERPROOF CONCRETE.
How 10 Prepare Mixture So II Is tn1-
 previous to Moisture.

How to Prepare Mixture So If ls tr1-
 previous to Moisture.
 Concrete is very largely employ cd in many building constructions. aud in some situations it Is very important that 1t should be at least practically waterproof. There are several methods of rendering concrete more or less i'm permeable to water. some simple and free 10 anyone. and some involving the use of secret of patented com pounds. Of the former the simplest method Is to mix hydrated lime or finely divided clay with the concrete, thus at least partially filling the voids or interstices in the concrete and de- creasing the percolation of water.
 Another simple method Is to mix powdered alum with the cement and dissolve ordinary soap in the water to be used in mixing the concrete. AL though the latter materials have been used for more than sixty years as a wash for rendering masonry impervi- Dus to water, and although in recent years they. have frequently been en- ployed as ingredients of concrete 10 make the entire mass impermeable. the proportions to be employed and the reason for the effect seem to have had little or no scientific consideration: at least the proportions used in practice vary very widely.
 To use the alum and soap method of decreasing the permeability of nor tar or concrete the alum in powdered form may be mixed with the dry ce- ment or the sand, and the soap may be dissolved in the water employed in mixing the concrete, or both the alum and the soap may be dissolved In the water. The former is probably the safer method in practice. since with the latter method the watef>must be thoroughly stirred while the two are being mixed. or the precipitate may form in large masses, which 1t Is prac- ucally impossible to break up; and further. the water must be kept stirred to prevent the compound from ac- cumulating Oh the surface. These are conditions that it is not always easy to be certain of securing. However, the alum is more easily dissolved than the soap. and hence the alum may be dissolved in. say. one-fifth of the water. and the soap in the remaining four f1fths, and then the two portions may be mixed together, being careful to stir them as the mixing progresses. The alum and the soap combine and form finely divided. 1occulent, insolubIe, water repelling compound. which fills fnn rF hn its permeability.
 The best proportions are. alum one part and hard soap two parts. both by weight Soap varies in its chemical composition. and hence a single pro- portion cannot be stated which will be chemically exact for all cases The above proportion is in round numbers. the relative combining weights of alum and average hard soap. and hence 1t is the best proportion to use although widely different proportions have been used in practice with suc- cess. Any reasonably pure soap will do. but if soft soap is employed a greater amount should be used in pro- portion to the amount Of water in it.
 II lS diucuAL tO ulSSOIV6 mOFe Iuun about per cent of hard soap in cold water. and hence this practically iim- its the amount of alum to 1.6 per cent and of the soap to 8 per cent These amounts will give a precipitate equal to about B per cent Of the weight of the total water. The amount of precip. itate formed in the pores of the mor- tar or concrete will depend upon the amount of water used in the mixing, Of course. if it be dissolved in small CT quantity of soap and alum the soap could be first dissolved in a smaller quantity Of hot water. which Is after ward mixed with the water used In making the mortar. but this is hardly practicable or necessary.