All materials experience some dimensional changes from expansion or contraction due to temperature variations. In building materials, there is also normally some movement due to creep, moisture, and the movement of adjacent materials. While StonePly is somewhat able to flex, joints should be used to allow for movement.
StonePly is generally designed using a coefficient of thermal movement of 0.0000045 in/in/degree Fahrenheit (0.0000081 mm/mm/degrees Celsius). The actual temperature change that the StonePly may be exposed to depends on the location of the project, the color of the Stone (dark colors absorbing more heat from the sun) and the direction of the wall exposure.
The most common sealant used with StonePly joints is silicone. Silicones provide excellent weather resistance, are easy to apply, have a low shrinkage rate, and can accommodate a large amount of movement. Sealants are generally specified under section 07920. Foam backer rod should be used.
For smaller StonePly panels, a 3/8" to 1/2" joint width is typical. Larger panels should be designed to have 1/2" wide joints or wider.