[432] Outdoor Whitewash of Lime or Chalk.

Manufacturer and Builder ?, 1872

A common remedy to make lime stand the weather is to put a solution of common alum in the lime whitewash. If the lime is not old, but freshly burnt, it combines while drying to an insoluble compound. If the lime is old, it is no better than chalk; in fact, it becomes similar to chalk. In this case you must use water-glass, or silicate of soda. This, mixed with the finely-ground chalk, makes a coat which water will not wash off, except when your water-glass contains a little too much soda. In this case you must cover your chalk coat with a second wash of a solution of chloride of calcium. This will take the soda out, and make the chalk coat stand the water better.

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