Stone Cold – masons at work

A significant portion of the building will be clad with stone veneer. I estimate that it is equivalent to about 40% of the exterior of the Visitor Center. The stone provides an esthetic quality to the building, contributes to the overall thermal value of the wall assembly and functions as a component of the rain wall system although not the most efficient material in this application.

The stone is specified to qualify for LEED credit MR5 which is Regional Materials. This means that the stone and the accessories are to come from within 500 miles of the job site.The contractor will need to verify this LEED credit with documentation which has not been received to date. The shape of the stone is to be as follows: split-bed, coursed broken-range ashlar with varying course heights of roughly 9″, 15″and 24″ and random lengths of 12″ to 48″ or more as indicated in drawings; the stone veneer shall have a thickness between 4″ and 6″, with chopped roughly squared edges; no more than 25% of the stones used should be 9″ tall with at least 30% of the stones used 24″ tall; the larger dimension of the stone shall always be horizontal. A sample panel (4′ x 4′ mock up) constructed at the site is required for approval prior to the stone being installed.

The application of the stone veneer is fully addressed in the specification section 044300 Stone Masonry. The stone is the first material in the exterior envelope assembly to take the brunt of lateral wind loads pushing on the wall. The stone veneer by itself cannot resist this load, so it must transfer the lateral forces to that part of the assembly designed for structural loads which are the metal studs. The transferring of this load is done thru ties that are spaced at 32″ o.c. horizontally with another row every 18″ vertically. The veneer ties must meet the following requirements:

• Structural Performance Characteristics: Capable of withstanding a 100-lbf load in both tension and compression without deforming or developing play in excess of 0.05 inch.
• Anchor Section: Sheet metal plate, 1-1/4 inches wide by 6 inches long, with screw holes top and bottom and with raised rib-stiffened strap, 5/8 inch wide by 3-5/8 inches long,
• stamped into center to provide a slot between strap and plate for inserting wire tie.
• Fabricate sheet metal anchor sections and other sheet metal parts from 0.067-inch- thick, steel sheet, galvanized after fabrication.
• Wire Ties: triangular, rectangular, or T-shaped wire ties fabricated from 0.188-inchdiameter, hot-dip galvanized steel wire.

The assembly requires the stone masons to maintain a minimum 1″ air space between the back of the stone and the exterior sheathing that is applied to the metal studs. The purpose of this gap is to allow ventilation of the space behind the stone and allow any accumulated moisture to collect at the bottom of the wall and wick to the exterior. The masons are to lay the walls with joints not less than 1/4 inch at the narrowest points or more than 1/2 inch at the widest points. The masons are to cover the tops of walls, projections, and sills with waterproof sheeting at end of each day’s work. A diagram of the full wall assembly taken from the construction drawings is shown below.

Any excess stone is to be properly dealt with by one of the following methods:

• Excess Stone: Stack excess stone where directed by Owner for Owner’s use.
• Disposal as Fill Material: Dispose of clean masonry waste, including mortar and excess or soil-contaminated sand, by crushing and mixing with fill material as fill is placed.
  • Crush masonry waste to less than 4 inches in greatest dimension.
  • Mix masonry waste with at least two parts of specified fill material for each part of masonry waste. Fill material is specified in Section 312000 “Earth Moving.”
  • Do not dispose of masonry waste as fill within 18 inches of finished grade.
• Excess Masonry Waste: Remove excess clean masonry waste that cannot be used as fill, as described above, and other waste, and legally dispose of off Owner’s property

The stone work has been going well, moving very quickly and will be completed soon.

As a follow-up to last week’s post, new vertical aluminum curtain wall tubes have arrived at the site to replace the ones that had holes drilled in the wrong locations and are currently being installed.