General Principles for Installation
Homes using adhered concrete masonry veneer (ACMV) may show signs of moisture damage after a short time if installers detail the wall as if it were actual stone or brick. ACMV, sometimes misleadingly called "manufactured stone," is a masonry product that behaves more like stucco. (It actually has more problems than stucco, as the ledges on the some profiles give rainwater a place to puddle and soak into the wall.)
ACMV manufacturers all have particular requirements for installing their products. The Masonry Veneer Manufacturers Association has a free Installation Guide on its website that shows several important details, as well. However, remembering the general principles listed below should decrease the chance of problems with all products in all parts of the house.
Design. Wide overhangs are a good idea on any structure but especially on ACMV. They greatly reduce the chance of water problems.
Framing. The structure should be fully dried before installing ACMV. Structural movement could crack the material, especially at joints.
Lath. Make sure to install metal lath horizontally with the cups facing up. Otherwise, the scratch coat could slide off the building. Wrap the lath around inside and outside corners. Only nail lath into framing members; do not drive nails through sheathing in the space between studs.
Scratch coat. Use a mix with a high cement content that cures hard. Clean sand is needed for a strong scratch coat.
Kickout flashings. Because ACMV is so intolerant of water, kickout flashings are crucial for avoiding moisture problems below roof-wall intersections. The kickout has to be sized to accommodate the thickness of the particular siding.
Vertical transitions. Where dissimilar materials meet, install a J-bead with a small gap. This allows you to create a flexible joint by installing backer rod and sealant.
Detailing ACMV
To avoid problems, ACMV must be detailed like stucco, not like brick or true stone veneer.
The drawing highlights the important waterproofing details. They include:
- A weather resistant barrier (WRB) consisting of two layers of paper or housewrap.
- Good flashing details that integrate with the WRB at penetrations and intersections.
- A drainage mat that creates a rainscreen between the WRB and the scratch coat.
- Weep screeds at wall bases and other horizontal transitions. These give any moisture that gets behind the siding a way to drain out.
