Managing Moisture Control, Shrinkage and Cracking

Reading Rock’s RockCast architectural stone products, like all concrete masonry products, may shrink slightly. The most common shrinkage/restraint issues come from drying shrinkage, temperature changes, carbonation and differential movement.

Kiln fired clay brick expands as it absorbs moisture and concrete masonry units shrink. This differential movement needs to be controlled when utilized with clay products.
IWR mortar additive should be included in the mortar mix when a water repellent wall system is required.
Control movement in the wall system. To do this, consider horizontal joint reinforcement, bond separation between different building products (Brick vs. Concrete Masonry), and the use of control joints. TEK Guide 5-2A outlines these parameters. For Concrete Masonry units used as a wainscot with brick above, bond separation should be considered with horizontal joint reinforcement every 16” o.x. or every course on 12” and 16” tall units and appropriate control joints. Please refer to the appropriate NCMA TEK Guide.
In using elastic (control) joints, refer to NCMA TEK Bulletins 10-1A Design of Concrete Masonry for Crack Control, 10-2B Control Joints for Concrete Masonry Walls- Empirical Method, 10-4 Crack Control for Concrete Brick and Other Concrete Masonry Veneers, and 5-2A Clay and Concrete Masonry Banding Details for guidelines. Refer to NCMA TEK Bulletin 3-6B Concrete Masonry Veneers for proper veneer anchoring.
Control joints are required at all openings, changes in wall height, between main intersecting walls, corners and for long running walls without openings at a distance of 1½ times the height of the masonry, as outlined in TEK Guide 10-2B. The empirical method notes that the distance is for the masonry only and if brick is used, it should be treated independently for “expansion: and the appropriate brick technical guidelines followed. The most common shrinkage/restraint issues come from drying shrinkage, temperature changes, carbonation and differential movement.

Tolerances

Only RockCast's Custom Cast Stone Series (wet method) is structural. All other RockCast architectural stone products are designed to carry only its own weight.
Maximum size ratio is generally 15 to 1. Units should not be manufactured longer or larger than 15 times the thinnest dimension.
Do not deviate by more than plus or minus 1/8” from approved cross-section dimensions.
Do not deviate by length of units by more than length/360 or plus or minus 1/8”, whichever is greater, not to exceed plus or minus ¼”.
Warp, bow, or twist: Do not exceed length/360 or plus or minus 1/8”, whichever is greater.
For installation tolerances comply accordingly:
- Variation from Plumb: Do not exceed 1/8” in 5’ or ¼” in 20’ or more.
- Variation from Level: Do not exceed 1/8” in 5’, ¼” in 20’, or 3/8”
maximum.
- Variation in Joint Width: Do not vary joint thickness more than 1/8” or ¼”
or normal joint width, whichever is greater.
- Variation in Plane between Adjacent Surfaces: Do not exceed 1/8”
difference between planes of adjacent units or adjacent surfaces indicated to
be flush with units.