Veneer Wall: Adhered Stone Veneer/Reinforced Concrete Block

• Interior walls where the weight or the thickness of full depth stone could be a problem
• Infill buildings in an historic district where you want the look of traditional masonry but want to minimize the thickness of the wall
• Single-family and multi-family residential, shopping centers and restaurants, low-rise construction
• Stone clad buildings look natural in mountain settings while the high fire resistance of this wall system is a real plus in wildfire areas
• Use thin adhered stone veneer where the weight and depth of the wall are more important than longevity

• Great design flexibility with many colors, textures, and types of stone available
• Has the appearance and fire resistance of a solid masonry building but walls are thinner and lighter than traditional stone veneer walls
• Minimal long-term maintenance

• By Code, adhered thin stone veneer must be kept at least 2” above pavement and 4” above grade. Do not bury the thin stone veneer in the ground.
• The stone veneer must lap at least 1” over the joint between the foundation and the CMU.
• This wall system does not have a drainage cavity. It can be difficult to make this wall completely weathertight unless you coat the exterior surface of the wall.
• Fully grouting the wall minimizes water penetration that typically comes through the head joints between blocks.
• Do not use batt insulation behind a single-wythe wall. If water leaks through the wall, it will saturate the batt insulation, inviting mold and reducing the R-value of the insulation. Rigid insulation boards can tolerate occasional moisture exposure.
• Exercise caution when using this wall system in climates with above average precipitation.
• In Colorado’s climate, single-wythe CMU walls have difficulty meeting the energy requirements of the International Energy Conservation Code unless you add insulation to the assembly. You can either build the wall with specialty units that include insulation within the wall, or you can add furring and rigid insulation on the interior face of the wall.  If you use Hi-R block, the wall will need to be at least 10” or 12” wide to allow enough room for the insulation inserts and the space for grout and rebar. Compliance with the IECC is not required for interior partitions that are not exposed to weather.

• Backup: Reinforced concrete block (CMU) wall
• Veneer: Natural stone veneer (3/4” to 2-5/8” thick)
• Insulation: Polyurethane foam in un-grouted cores of the backup wall + 2-inch rigid extruded polystyrene on the inside face of the CMU wall (Reference: Colorado Masonry Systems Design Guide, Chapter 7, Table 7-1 and Figure 7-3)
• Flashing: Use a proprietary flashing system at the base of the wall to lead moisture out of the wall without compromising the structural connection from the CMU to the foundation.  Details showing these flashing products are shown here under “System Details”.
• Mortar: Type S, Portland cement/lime, plain gray. Adding a bonding agent to the mortar can make the stone adhere to the back-up wall more aggressively, but it will also make the mortar more difficult to clean. 
• Joints: Struck flush

• In areas with high seismic risk, masonry reinforcing might have special requirements. Check your local building codes.
• Do NOT call for dry-stack mortar joints in adhered stone veneer in Colorado. Our severe weather can cause premature failure. 

• Fire Rating = 4 hours

• 1” thick stone veneer                                 12.00 psf
• ½” to 1” thick setting bed                          10.00 psf
• 8” concrete block                                       20.25 psf
  CMU @ 105 pcf (25% grouted solid 75% foam-filled cores)
• 2×2 wood furring                                         0.70 psf
• ½” gypsum sheathing                                 2.20 psf  
• TOTAL weight of wall                                45.15 psf

• STC = (weight of wall)^0.233 x 21.5
• STC = 50.83 dB

Reference: NCMA TEK Note 13-01C

• R-value: 16.94 to 17.11
• Calculations
  • Outside air film                                          0.17
  • ¾” thick stone veneer                               0.12
  • ½”to 1” thick setting bed             0.16 to 0.33
  • 8” concrete block                                       5.26
    CMU @ 105 pcf (25% grouted solid 75% foam-filled cores)
  • 2” XPS insulation board                          10.00
  • ½” gypsum sheathing                                0.45
  • Interior air film                                           0.78
  • TOTAL                                         16.94 to 17.11

Reference: NCMA Tek Note 06-02C
Reference: International Energy Conservation Code, Tables C402.1.3 and C402.1.4

• Thin stone veneer is more fragile than a full-depth stone veneer. It needs movement joints at 16’-0” on center, maximum. Call for control joints near outside corners and around window and door openings to manage this differential movement without cracking. Align the control joints in the veneer with the control joints in the CMU backup wall.  For more information, read NCMA Tek Note 10-02D 
• There are three different pathways to meeting the requirements of the International Energy Conservation Code (IECC). You can use R-values to satisfy the prescriptive limits of Table C402.1.3 of the code. Using R-values requires continuous insulation in the wall in all Colorado climate zones. Following Table C402.1.4 of the code uses U-values to meet the insulation requirements. This approach does not require continuous insulation in the wall. A third approach is to use computer software like COMcheck to prove that the building meets code. Computer software is the most complex, but it is also the most flexible option.
• Do not use batt insulation. This wall system is essentially a barrier wall and does not have the drainage layer of a cavity wall. If moisture gets through the exterior wall, it will cause the batt insulation to mold.
• Call for rigid insulation on the inside face of this wall. Do NOT try to put the rigid insulation on the outside face of the wall (between the masonry veneer and the CMU). The weight of the veneer can cause the rigid insulation to shear in two, leading to failure of the entire system.
• Make sure you have at least ¾” overlap between the door and window jambs and the stone veneer. Install backer rod and sealant at the joints where different materials meet.
• Call for a saw-cut (smooth) edge where stone meets door or window jambs or control joints.
• Do NOT call for dry-stack mortar joints in adhered stone veneer in Colorado. Our severe weather can cause premature failure.
• You can save time by substituting a one-layer proprietary bonding mortar in place of both the scratch coat and bond coat shown in this drawing. See System Details.
• Use a proprietary flashing system at the base of the wall to lead moisture out of the wall without compromising the structural connection from the CMU to the foundation. Details showing these flashing products are shown here under “System Details”.
• It is difficult to quantify craftsmanship in a stone veneer installation. RMMI advises you to call for a Sample Panel to be built before you start the final installation. That way the masonry contractor, architect and owner can define acceptable installation standards early in the project. (See image of Poor Craftsmanship under System Details.)
• Calling for Coursed Ashlar Stone might save you money. It will also cut down on waste. Coursed stone is supplied in specific sizes, based on the height of the stone. Three-height coursed stone arrives on site with the stone cut in a combination of full-height, 1/3 of full height and 2/3 of full height. (Four-height coursed stone comes in full height, half height and 1/4 of full height). While coursed ashlar stone costs a bit more at the quarry, it cuts down on labor and installation costs because it simplifies the puzzle of installing the stone. Random Uncoursed Ledgerock looks more rustic. Coursed Ashlar Stone looks more controlled. (See images of coursed and uncoursed stone patterns in System Details below.)

• Spread a full mortar bed on the back of each stone. Do not leave air gaps behind the stone veneer.
• Use a proprietary flashing system at the base of the wall to lead moisture out of the wall without compromising the structural connection from the CMU to the foundation.  Details showing these flashing products are shown here under “System Details”.
• You can minimize the cleaning by laying the stone veneer from the top of the wall down to the bottom. This keeps mortar droppings from landing on veneer below your work. The mortar you are using needs to be stiff enough and sticky enough to hold the veneer in place without relying on veneer below to resist the pull of gravity.
• If you are using a mortar additive to increase bond strength, be careful to minimize mortar droppings. The additive makes it more difficult to clean these mortar blobs off the wall when you are done.
• If your project includes outside corners, start the pattern by laying the specialty corner units first.
• You can save time by substituting a one-layer proprietary bonding mortar in place of both the scratch coat and bond coat shown in this drawing. See System Details.
• This Wall Type shows rigid insulation installed on the inside face of the wall. Do NOT try to put the rigid insulation on the outside face of the wall (between the masonry veneer and the CMU). The weight of the veneer can cause the rigid insulation to shear in two, leading to failure of the entire system.
• If you are doing high-lift grouting, a rebar positioning device can help you keep the rebar in place where it will give maximum structural effect. See example.