Sponsored by:
- Commercial and institutional buildings
- Multi-family residential buildings
- High-end single-family homes
- Buildings requiring a high fire rating
- Noisy environments
- Solid, classic stone exterior works especially well in mountain settings—plus the high fire rating protects the house from wildfires
- Most types of stone have exceptional durability
- Minimal long-term maintenance
- Less flexible, less prone to rot and rust than a wood-stud or steel-stud backup wall
- Excellent insulating values with great heat capacity
- Inherently fireproof with fire ratings up to 4 hours
- Rough surfaces discourage graffiti
- Great for noisy environments – naturally absorbs sound
- One trade erects both the structural and skin layers of the wall
- Lower life cycle costs offset a higher initial cost
- This substantial wall system may require larger foundation
- Backup: Lightweight (105 pcf) plain gray concrete block (CMU), 8″ x 8″ x 16″ (nominal)
- Vertical Reinforcement: #6 vertical reinforcement @ 32″ on center
- Horizontal Reinforcement: 9-gauge joint reinforcement @ 16″ on center (every other course)
- Veneer: 4” thick natural sandstone veneer, laid in random ashlar pattern
- Cavity: 3-inch air space
- Insulation: 2-inch rigid extruded polystyrene in the drainage cavity (Reference: Colorado Masonry Systems Design Guide, Chapter 8, Table 8-3)
- Flashing: Self-adhered bitumen flashing paired with metal drip edge; weep vents (Reference: Colorado Masonry Systems Design Guide, Chapter 6, Shelf Angle Flashing Options, Fig.6-3 (Option 2))
- Masonry Ties: Pintle-eye ties linked to the horizontal reinforcing
- Mortar: Type N, Portland cement/lime, plain gray in the CMU backup wall
- Joint finish: Concave tooled mortar
- In high seismic zones, the CMU back-up wall is required to have additional horizontal bond beams to resist earthquake loads. Check with your structural engineer to verify requirements in your area. These bond beams can take the place of horizonal reinforcement in the structural back-up.
- Bond beams can replace the necessity for joint reinforcement in the CMU back-up wall but ladder-eye horizontal reinforcing is the easiest way to tie the veneer to the CMU.
- Fire Rating of a multi-layered cavity wall = (Rating1 0.59 + Rating2 0.59 + 0.3)1.7
- Stone veneer + CMU grouted @ 32″ on center: 4 hours
- Stone veneer + CMU fully grouted: 4 hours
- CMU grouted @ 32” on center: 91 pounds per square foot
- CMU fully grouted: 126 pounds per square foot
- STC = (weight of wall)0.233 x 21.5
- Grouted @ 32” on center: STC = 60.28 dB
- Fully grouted: STC = 64.95 dB
- R-value: 12.92
- Calculations
- Outside air film 0.17
- 4″ Stone veneer 0.62
- 2” EPX board 10.00
- 8” CMU, grouted at 32” on center 1.45
- Interior air film 0.68
- TOTAL 12.92
Thermal mass benefit: “Thermal Advantages of Masonry Walls” by David Woodham, PE
Reference: NCMA TEK Note 06-01C
- Place rigid-board insulation in the drainage cavity to maximize interior usable space and take advantage of the huge thermal mass provided by the masonry backup system.
- Anchored veneer will last longer than adhered veneer.
- Denser stones are typically more durable and more water repellent than lighter-weight or more absorbent stones.
- Don’t forget to include movement joints in the wall. Construct control joints in the CMU backup wall as per advice in NCMA Tek Note 10-02D. Installing movement joints in stone veneer is more of an art than a science. Use Tek Note 10-02D to tell you where the backup wall is likely to crack. After installing the stone veneer without movement joints, you can direct the crack by saw-cutting 2/3 of the depth of the veneer at these points. The thin saw line will be the weak point of the wall and will direct the crack. No need to install backer rod and sealant in this joint.
- Shelf angles may not be required for veneer support at every floor line. Cut down on the number of shelf angles to save money and simplify construction. If your CMU veneer is less than 30’ above the top of the foundation, it might not need relieving angles at all.
- 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.)
- Always use horizontal reinforcement in concrete block walls to control shrinkage cracks.
- It is difficult to build stone veneers with a drainage cavity because the variable stone thickness can make the veneer unstable. Slushing the collar joint full as the stone is being laid stabilizes the veneer. Vertical strips of drainage fabric will still allow moisture to drain to the flashing at the base of the wall.
- If you are laying round stones like river rock in the veneer, you can use wire ties to hold the stone in place until the mortar sets up. Once the mortar is cured, you can clip the wires and add pointing mortar to cover the ends of the wire. Use galvanized wire to avoid leaving rusty stains on the stone from corrosion of the wire.
- Lay sandstone, slate and other sedimentary stones with bedding planes laid horizontal.
- Simplify construction by requesting to use the same mortar type on the veneer as the backup. Type N is usually fine for both, except in high seismic zones where Type S is required.
- 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.
- Use 16” wide rigid insulation that will fit neatly between the eyes of the horizontal reinforcing. Use the legs of the pintles to hold the insulation board securely against the CMU back-up, leaving the cavity open for drainage.
- If the design calls for insulation in the cavity, you might consider using full sheets of insulation paired with standard two-piece adjustable anchors screwed to the face shells of the CMU instead of using pintle/eye horizontal reinforcing to tie the two wythes of the wall together. This system allows you to use large sheets of rigid insulation and minimizes the amount of time spent taping seams between pieces of insulation. Reference: Colorado Masonry Systems Design Guide, Chapter 6, Table 6-4
Flashing
Self-Adhered Flexible Flashing: This tough, flexible flashing strip comes with a removable release liner for easier installation. The liner MUST be removed to allow the sticky layer of the flashing to self-heal around any punctures from nails or screws. If the sticky layer of the flashing is bitumen, hold this flashing at least ½” from the edge of the masonry so that the tar layer does not melt and form ugly black drips on the face of the wall. Bitumen-based flashing is often paired with a metal drip edge which can be exposed to sunlight. This flashing will stick to masonry, concrete, gypsum, wood, or steel.
Base of Wall —Flash Vent Self-Adhering SS Flashing with Drip Edge
Roof to Wall Parapet Detail —York 304 SA Self-Adhering Stainless Steel Flashing (view from face of wall) 
Roof to Wall Parapet Detail —York 304 SA Self-Adhering Stainless Steel Flashing (view from roof) 
Joint Reinforcement
Ladder Horizontal Reinforcement: Adds tensile strength to the wall and helps control shrinkage cracking. The cross rods of Ladder Reinforcement are spaced at 8” on center so they align with the cross webs of the concrete block. This keeps the core holes open and makes it easier to place grout in the wall.
Masonry Anchors & Ties
Split-Tailed Stone Anchor: Allows you to tie two stones in place with each anchor. Set each clip of the anchor into a slot in the edge of the stone and secure the clip with mortar. Due to the variability of stone installation, sizes and thickness of stone anchors are usually designed and specified by a structural engineer.
Double-Pin Stone Anchor: Allows you to tie two capstones to the top of the parapet with each anchor. Drill an over-sized hole in the ends of each piece of the masonry cap. Insert a pin into the fresh mortar and then attach the angle of the anchor to the top edge of the structural wall.
H-B Stone Anchor #433
Cap with Pins
Rubble Stone Anchor System: A continuous vertical rod is threaded through eyes that project from the horizontal reinforcing in the CMU back-up wall. Veneer ties are integrated with this vertical rod, allowing complete vertical adjustability in placement of the ties. This system makes it easy to accommodate a wide variance in stone size.
Stonework Details
Poor Craftsmanship in Stonework
Random Uncoursed Stonework
Three Height Coursed Ashlar Stonework
Four Height Coursed Ashlar Stonework