As the mortar in the exposed edges of the joints is especially subject to dislodgment through the expansion and contraction of the masonry and the effects of the weather, it is customary after the masonry is laid to refill the joints to the depth of half an inch or more with mortar prepared especially for this purpose.
This operation is called pointing.
Pointing is generally done as soon as the outside of the building is completed, unless it should be too late in the season, when it should be delayed until spring. Pointing should never under any circumstances be done in freezing weather. It is also not desirable to do it in extremely hot weather, as the mortar dries too quickly.
Portland cement mixed with not more than an equal volume of fine sand and such coloring matter as may be required, with just enough water to give the compound a mealy consistency, makes the most durable mortar for pointing. If the stone is stained by cement, Lafarge cement should be used, or a putty made of lime, plaster of Paris and white lead.
Before applying the pointing the joint should be raked out to the depth of an inch, brushed clean and well moistened.
The mortar is applied with a small trowel made for the purpose and then squeezed in and rubbed smooth with a tool called a jointer (Fig. 120) and made for that purpose. Jointers are made with both hollow and concave edges, so as to give a raised or concave joint, as shown in Fig. 121. The concave joint is the most durable, although the raised joint makes perhaps the handsomest work.
Cleaning Down. - This consists in washing and scrubbing the stonework with muriatic acid and water. Wire brushes are generally used for marble work and sometimes for sandstone, but stiff bristle brushes usually answer the purpose as well. The stones should be scrubbed until all mortar stains and dirt are entirely removed. The cleaning down is done in connection with the pointing.
For cleaning an old front the sand blast, using either steam or compressed air, does the work most effectively, as it removes from 1/64 to 1/32 of an inch from the surface of the stone, making it look like new. Even carving can be successively treated in this way.