Mastic for stop-ping up holes, leakages, or cracks in marbles, is made with gum lac, coloured, as nearly as possible, to imitate the marble upon which it is used. Sometimes the gum is mixed with marble dust passed through a silken sieve; in other cases little pieces are used, which are cut and adjusted in the hole to be repaired, and glued there with the gum mastic - the precaution being first taken to heat the marble and the pieces, and to take measures for producing a perfect cohesion.

Cement Mastic

(a) Thick mastic is composed of 2 parts wax, 3 of Burgundy pitch, and 8 of rosin; melt and throw into spring water to solidify the paste, then roll it into sticks, and, in using it, melt only so much as is immediately required; this will preserve its strength, as it becomes more brittle by repeated heating.

(6) Corbel mastic is used in seams of the flagging of stairways and terraces. Six parts of the cement of good Burgundy tile without any other mixture, pass it through a silken sieve, add 1 part of pure white-lead, and as much litharge, steep the whole in 3 parts of linseed oil and 1 of lard oil, and preserve in cakes or rolls as the preceding. All the materials used should be thoroughly dry, so that they may perfectly mix with the oil which unites them.

(c) Fountain mastic is made of the rubbish of stoneware or of Burgundy the, amalgamated with thick mastic in such a manner as to form a paste proportioned to the use for which it is required; this is one of the easiest to prepare.

(d) Mastic of filings is employed in places which are usually damp, or which constantly receive water, as curb stones, flaggings of kitchens, bath-rooms and water-closets, and stone troughs composed of several pieces, either separate or clasped. This mastic is composed of 26 1/2 lb. of iron filings, or of iron and copper, which must not be rusty, 4 1/2 lb. of salt, and 4 garlics; this is infused for 24 hours in 3 1/2 pints of good vinegar and urine; it is then poured off, and the thick paste which is found at the bottom of the vessel is the mastic, which should be immediately used.

These mastics should be used upon materials which are perfectly dry, otherwise they do not incorporate well. Choose dry weather, and open the seams well with a curved, sharp instrument, finally polishing them with the chisel. Before laying the mastic, remove the dust from the seam by blowing info it with bellows; a long, straight, iron chafing dish, closed at the bottom, with the grate elevated about an inch to obtain a current of air, is then passed over the seam; this chafing dish is filled with burning charcoal, the heat of which draws out the moisture from the stone or marble. The slightest dust or dampness hinder the adherence of mastic. (See also ii. 93.)

Cold Mastic

Hydrochlorate of ammonia, 2 parts; flowers of sulphur, 1 part; iron filings, 16 parts. Reduce these substances to a powder, and preserve the mixture in closely-stopped vessels. When the cement is used, take 20 parts of very fine iron filings, add 1 part of the above powder, mix them together, adding sufficient water to form a manageable paste; this paste, which is used for cementing, solidifies in 15 days or 3 weeks, in such a manner as to become as hard as iron.

Masons Mastic

Pulverised baked bricks, quick-lime, wood ashes, equal parts. Mix thoroughly, and moisten with olive oil. This mastic hardens immediately in the air, and never cracks beneath the. water.