To Clean an Old Roof
Those wishing to know the best means of removing moss and earth accumulations from an old shingle roof, are advised to sprinkle lime freely along the comb of the roof, and let the rains dissolve and carry it over the shingles. Every particle of dirt and moss will be removed by it. If kept clean, shingles will last much longer. This method is as good and cheaper than any direct application to the shingles.

The Farm and Household Cyclopędia - circa 1888