Masonry Magazine December 2005 Page. 26
CAST STONE
Because shrinkage is expressed as a percentage, individual cast stone elements will experience actual shrinkage depending upon their length. For example, a 24-inch long unit with a linear dry shrinkage of 0.065% will experience a total shrinkage of 0.016 inches. A 144-inch long unit with the same shrinkage will experience a change in length of 0.094 inches (approx. 3/32 inch). Determination of an overall limit on the length of cast stone elements should consider shrinkage, but also self-weight/flexure of the element, handling limitations, anchorage type and desired appearance with respect to cracking.
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Cast stone units laid in mortar should follow the same recommendations as other masonry units. The location of control joints in walls with cast stone will depend on the materials used in the entire wall. When cast stone is used as an isolated accent in clay brick walls, recommendations for expansion joints for clay brick should be followed. For isolated accent pieces, no other special requirements apply.
When cast stone banding is used in clay brick walls, the spacing of vertical expansion joints for clay brick and the spacing of control joints for concrete masonry should both be examined. The expansion joints spacing should be based on the most stringent requirement. In addition, the Brick Industry Association recommends providing a bond break between the clay brick and concrete or cast stone banding to accommodate the differential movement that will occur. In this case, flashing is often placed either directly above or below the banding course. Using a bond break both above and below the banding course is not recommended unless proper mortar embedment of the anchors in the veneer can be achieved.
Loadbearing units should be reinforced as necessary. Panels, soffits and similar stones should be reinforced according to ASTM C1364. Lintels and large panels must be kept vertical or they will be prone to cracking. Remember, they should be handled only in the same orientation as they will be installed in the structure.
For best practice, limit lengths of units to no more than 15 times their effective cross-section thickness.
Job Site Planning
ON-SITE PERSONNEL should be familiar with the applicable sections of the Cast Stone Institute's specifications and the project specification pertaining to delivery, storage, setting, patching, cleaning, pointing and sealing. Where the project specification does not include a particular issue, the industry standards should be followed. The Cast Stone Institute publishes several technical papers that are useful to stone setters, including Technical Bulletin #37 Job Site Handling and Installation, which is available at www.caststone.org.
The following are just a few of the tips that masons and mason contractors should follow:
• Upon delivery, all cast stone should be checked for chips, cracks, stains or broken pieces. Any damage should be noted on the delivery slips and communicated to the manufacturer or the sales representative.
Prior to setting, insure climatic conditions are within thermal limitations of the mortar. Cold weather setting practices are basically the same as the International Masonry Industry All Weather Council (IMIAC) recommends for unit masonry. Mortar retarders and accelerators should be used according to manufacturers' directions, but not with patching material. Set stone in full mortar joints and fill all dowel holes and anchor slots completely with mortar. Be sure uniform joint widths are within specifications tolerances.
• Ensure that all specified flashing and dampproofing is installed. Flashing pierced by stone anchors must be sealed either by metal thimble, grommet or approved sealant. Flashing locations are the responsibility of the architect and should not be assumed by the mason under any circumstances.