- Institutional buildings, including museums, places of worship, universities and schools; healthcare facilities; hotels, restaurants and shopping centers; sports stadiums, theaters and casinos; high-end single family and multi-family residential buildings
- Buildings requiring a high fire rating
- Noisy environments
- Sophisticated solid stone exterior over a robust structural concrete block backup system—works especially well in urban settings
- Most types of stone have exceptional durability
- Minimal long-term maintenance
- Nearly unlimited design flexibility with many types of stone, many colors, and surface textures available
- The continuous concrete block (CMU) backup wall permits anchor attachment anywhere within the field of the wall. Stud backup systems require added structural framing, placed precisely at stone anchorage points.
- Excellent heat capacity
- Inherently fireproof with fire ratings up to 4 hours
- Great for noisy environments – this heavy wall naturally absorbs sound
- One trade erects both the structural and skin layers of the wall
- Lower life cycle costs offset a higher initial investment
- Don’t expect a perfectly uniform appearance. Stone is a natural product and there will be variations in color, veining, and surface texture.
- This substantial wall system may require larger foundation
- Backup: Lightweight plain gray concrete block (CMU), 8” x 8” x 16” (nominal)
- Vertical Reinforcement in backup: #6 vertical reinforcement @ 32” on center
- Horizontal Reinforcement in backup: 9-gauge joint reinforcement @ 16” on center (every other course)
- Veneer: 2” thick limestone panels, honed finish. Face size: 24” wide x 24” tall, stacked bond. Alternate: Stone 24” wide x 8” tall, running bond
- 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: Type 304 stainless steel double-split-tail anchors for stone veneer
- Mortar: Type N, Portland cement/lime, plain gray in the CMU backup wall
- Joint finish: Backer rod and sealant at all stone joints
- In areas with high seismic risk, masonry ties and anchors might have special requirements. Check your local building codes.
- 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.
- Fire Rating of a multi-layered cavity wall = (Rating1 0.59 + Rating2 0.59 + 0.3)1.7
- Backup wall grouted @ 32” on center: 3 hours
- Fully Grouted backup wall: 4 hours
- Stone slab + CMU grouted @ 32” on center: 67 pounds per square foot
- Stone slab + fully grouted CMU: 102 pounds per square foot
- STC = (weight of wall)0.233 x 21.5
- CMU grouted @ 32” on center: STC = 57.27 dB
- CMU fully grouted: STC = 63.16 dB
- R-value: 13.57
- Outside air film 0.17
- 2″ sandstone slab 0.30
- Air gap 0.97
- 2” EPX board 10.00
- 8” CMU, grouted at 32” on center 1.45
- Interior air film 0.68
- TOTAL 13.57
Thermal mass benefit: “Thermal Advantages of Masonry Walls” by David Woodham, PE
Reference: NCMA TEK Note 06-01C
- Stone anchorage requirements are not prescribed by building codes. Anchors need to be engineered for each project. The choice of anchor depends on the size of the panel, the stone type and local weather and seismic requirements.
- Stone anchorage design is very conservative. In some cases, you can reduce the number of anchors needed by conducting anchor strength tests on stone samples identical to those being installed.
- Be very careful using epoxy connections where they will be subjected to sustained tension loads. Many epoxies will creep and fail over time.
- Use bent anchors in field-cut kerfs or continuous slots where possible. Pin anchorage can require tight construction tolerances.
- Be careful using thin stone panels which are prone to breakage and require more anchors than a thicker panel.
- Some stones like marble will warp over time if the panels are too thin.
- Mortar is acceptable for installation of small-sized stone panels. Use Type N mortar for the stone veneer. It is more flexible and less likely to have joint cracking.
- This wall system features slabs of stone installed on a robust CMU backup wall. Type N mortar works fine here. If you choose instead to install stone slabs (24” or larger) over a flexible structural system like steel or wood studs, use backer road and flexible sealant in joints between panels to avoid cracks between the mortar and the stone slab. (See System Details below.)
- Sealants can bleed into surrounding stone. Check with the stone supplier and the sealant manufacturer for recommended sealant types. You might need to prime the edges of the stone to accept sealant. Test sealant compatibility on the Sample Panel. (Reference: Colorado Masonry Systems Design Guide, Chapter 5)
- Use stainless steel anchors to attach stone panels to the backup wall. This will minimize corrosion and staining on the face of the stone.
- Isolate dissimilar metals (such as stainless steel and bare steel) with plastic washers to prevent galvanic corrosion.
- Fill anchor slots in stone slabs with flexible caulk after placement to prevent water from collecting in the slot and cracking the stone.
- Don’t fill anchor slots with gypsum cement (plaster of Paris) which can expand and crack the anchor slot.
- Hidden lintels installed in kerfs cut into the back of the stone slab can lead to stress concentrations leading to cracks telegraphing through to the face of the stone.
- 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.
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)
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