By Bud Coburn
Manufactured stone is a lightweight, man-made concrete masonry product that is typically cast into random sizes in a variety of colors and finishes meant to mimic the look of quarried rock. It is generally applied as a masonry veneer to exterior and interior walls, columns and landscape structures.
InterNACHI inspectors are likely to come across manufactured stone during inspections, and will want to be familiar with the details of this building material, as well as some of the problems associated with it. Water damage due to incorrect installation is a significant area of concern, and inspectors and homeowners alike can benefit from knowing how this can occur.
Manufactured Stone vs. Cast Stone
Manufactured stone is often referred to by many different names. While in most instances, the various names can be used interchangeably, manufactured stone is notsynonymous with cast stone. Manufactured stone is a different product entirely. Cast stone is a refined architectural concrete building unit whose appearance is meant to simulate quarried stone, but is generally built into a load-bearing masonry wall system. This is a different purpose from the lightweight veneer created with manufactured stone. These two products are manufactured according to different standards and are intended for different applications, although they are often confused with each other.
Pros and Cons
Manufactured stone provides some benefits over quarried rock. However, there are some important concerns to be aware of.
- Although manufactured stone is basically nothing more complicated than standard cement, the molding and coloring process allows for it to be made almost indistinguishable from real quarried stone. It can be molded and colored to look like a wide variety of different stone facings.
- As a lightweight veneer, manufactured stone allows the aesthetic of a real stone structure to be achieved simply and cost-effectively.
- Manufactured stone veneer can be applied to wood frame, masonry and metal structures, and does not require foundational support.
- When properly installed and maintained, manufactured stone is extremely durable and will last for many years.
- Proper installation is absolutely critical with this product. Incorrect installation of manufactured stone veneer on an exterior wall can lead to serious damage from water penetration, occurring even over a relatively short period of time. There have been reports of serious foundation rotting due to improperly installed veneers in homes less than two years old.
- Though the pigment used to color the manufactured stone is generally durable and will not fade, de-icing salts, harsh chemicals, cleaning solvents and paint thinners can cause discoloration and staining.
- It has been reported that manufactured stone used around swimming pools can be discolored by chlorine.
Similar to what has become a common problem with synthetic stucco, improper installation of manufactured stone veneer on exterior walls has lead to serious concern about water damage. Improper flashing and drainage details behind the veneer are often the culprit, just like with synthetic stucco, but the damage with manufactured stone can often be more severe. This is because, unlike synthetic stucco, manufactured stone is not installed with an air space between the cladding and the framed wall. When the veneer is saturated with water during a rainstorm, it holds rainwater right up against the framed wall. With little drainage or drying space, housewrap (or building paper) and flashing have a harder time diverting the moisture. If care is not taken during installation to cover every detail properly, serious water damage may result under relatively normal weather and seasonal conditions.
Manufactured stone veneers share many similar concerns with synthetic stucco. Proper seams at windows and doors are important, and building paper or housewrap must be lapped correctly in order to keep water diverted from the framed wall. Window pan flashings can be helpful if correctly installed. Bottom terminations of manufactured stone veneer are best equipped with weep screeds of some kind in order to avoid the pooling of water at the lowest points, which can cause those areas to stay continuously wet. The tops of windows and door openings are also spots that will benefit from weep screeds.
Another issue can arise when manufactured stone is paired up with a different material on the same wall. Synthetic stucco, for example, is often installed on part of a wall, with the rest of the wall covered with manufactured stone. Water will penetrate to the wood-frame wall and cause damage if the seam between the two claddings is not properly managed during installation.
The most important thing to look for when inspecting an exterior wall clad in manufactured stone is correct installation. Even if there is no visible water damage, steps must be taken to guard against it. Here are some things InterNACHI inspectors can keep in mind when examining these walls.
- The base of wood-frame walls need weep screeds, as do the tops of windows and door openings.
- In order to avoid water penetration at the seams at windows, doors and adjacent trim, as well as at seams and joints where manufactured stone meets another form of cladding, these seams should be sealed. Corrosion-resistant flashing with a drip edge should be installed with a bedding seal included under the flashing. A water-resistant barrier should lap over the back edge of the flashing for positive drainage. A piece of manufactured stone veneer with an edge that slopes away from the building is also beneficial for use here.
- In order to ensure proper drainage and to avoid the possibility of termites tunneling through it, the veneer should not be in contact with the ground or pavement.
- The veneer should not be in contact with roofing materials.
- If the veneer has been installed correctly, there will be nothing other than mortar visible between the stones.
- Kick-out flashings should be installed everywhere they are needed, and should divert water away from the manufactured stone veneer and the building in general. If proper detailing and flashing are not installed, water may penetrate the cladding and cause structural damage from rotting.
- The manufacturer’s instructions for the particular AMSMV product installed should always be followed by the installer.