Making lime and mortar for walls, vaults and cisterns
Slaking lime, choosing sand, the Roman practice of long-covered lime, and why sea sand cracks vaults
Folio 87v is a treatise-like note on lime and mortar for building. Leonardo gives the slaking of alberese lime, the proportions of lime to river sand, the superiority of travertine and flint limes for rendering and paving, and mixtures for cistern plaster. He records the Roman practice of storing slaked lime under sand for years before use, citing lime found buried in Rome still perfect after centuries, and warns that salty sea sand cracks vaults and must be weathered by rain before use in walls.
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Slaking and mixing lime with sand
Alberese lime must be slaked at once, straight from the furnace, with plenty of water, since too little inflames it and makes it behave like sand. Mix two parts of river sand to one of lime (three to one for other limes); travertine and spongy-stone lime is the best for rendering and plastering walls.
Best limes and mortar for cisterns
The flint (selice) with which the ancient Romans paved their roads makes the best lime of all, abundant in the mountains of Radicofani. Adding a third part of pounded old potsherds or tiles gives an excellent mix; for cistern walls compose two parts of lime to five of harsh, rough sand.
Aging lime under sand, after Roman law
Once slaked, the lime is gathered into a heap and well covered with sand, and the longer it stands the more perfect it becomes. The Romans forbade its use before three years covered, and lime found buried twenty feet down in Rome after hundreds of years was still most perfect.
Choosing sand; why sea sand fails in vaults
Sand is worthless unless harsh and dry, so that squeezed in the hand it does not cling and, shaken from a cloth, leaves no soiling. Sea sand is bad in vaults because its salt always weeps and fills them with cracks; if used in walls it should be laid over time so the rains purge its saltiness.