Summer 2006
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Installed MTI Sure Cavity weep system and wall opening weeps.
Photo courtesy of Masonry Technologies, Inc.
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Water Drainage:
By Mark Haverstock
There's a longstanding joke in the waterproofing industry — most waterproofing systems work well when there is no moisture. But in the real world, moisture is a fact of life in most climates where natural thin stone is installed. To maintain wall integrity and prevent problems such as water seepage, mold or other types of damage, architects and installers need to plan for the inevitable fact that if water is present, it will likely find a way in.
Successful moisture control involves two steps: one is waterproofing and the second is drainage — keep as much water out of the wall system and remove any trapped water as quickly as possible. "Think of constructing your wall from the inside out — you start with the backup wall and end with the stone veneer," said Michael J. Scheffler, a senior consultant for Wiss, Janney and Elstner Associates. "Unless there is sufficient attention paid to moisture control at both steps, you're going to end up with problems."
The Physics Behind Water Movement
Water moves in mysterious ways, but it's all explainable. Here's the science behind it:
Capillary action is defined as the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion and surface tension. Capillary action occurs because water is sticky — water molecules stick to each other and to other substances, such as glass, cloth, organic tissues and soil. Dip a paper towel into a glass of water and the water will "climb" up the paper towel. In fact, it will keep going up the towel until the pull of gravity is too much for it to overcome. Weep systems use this principle along with gravity to remove water.
Gravitational pull on water is one force that moves it from a high point to a lower point. Water will move in a downward direction unless it is blocked by a heavier material or something that is held in the water's path. Cavity walls and weep systems use the force of gravity to evacuate water.
Vapor Drive occurs as warmer, more humid air is drawn to colder surfaces and seeks to penetrate or drive into the insulation and spaces between inner and outer walls. If the humid air begins to cool or condense, especially on non-permeable materials such as paint, metal or glass, water molecules bond together to create liquid water. The water may then begin "puddling" at low points in the wall.
Air pressure equalization happens when air with higher pressure moves toward areas of lower pressure. The air movement can cause water that may be present in or on wall voids to be pushed into a building where the air pressure is lower. This is also the case with wind-driven moisture, rain and waves of unequal air pressure.
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To date, full and thin veneer installation have generally focused either on vapor barriers, flashing or just sealing exposed sections of walls. Not much thought is given to multiple preventive measures or incorporating drainage planes, which could avoid problems down the road.
"It's unfortunate that much of my customer base is made up of people that have experienced failures and paid for them, or they have close associates who have experienced failures and paid for them," said John H. Koester, CEO of Masonry Technology Inc. "Traditionally, the industry has not really been open to using preventive measures. Now some major companies are finally coming out and saying you need drainage planes for thin veneer — period."
Several methods have been used over the years to avoid or control water problems in natural stone installation. The following is a brief discussion of the pros and cons of each.
Barrier Systems
Historically, most stone masonry walls were constructed as barrier walls. "The thickness of masonry between the exterior and interior surfaces was normally sufficient to prevent large amounts of water from migrating all the way through it," said Eric Peterson, an associate at Whitlock, Dalrymple, Poston and Associates. "The massive and solid wall construction forces water to travel a long distance though small interstitial spaces to get from one side of the wall to the other." The typical barrier wall would have the joints and cavity spaces between stones solidly filled with mortar creating a monolithic system and hence a barrier to prevent water from being transmitted through to the interior.
Completed stone wall showing wall opening weeps.
Photo courtesy of Masonry Technologies, Inc.
But the more modern thin stone generally provides only two inches or less of barrier and is attached directly to the wall, providing a much smaller buffer. Care must be taken during the installation process, or water may eventually find its way behind these relatively lean surfaces.
Kevin Schultz, masonry consultant for Buechel Stone, points out that it's not so much the stone, but the mortar that can be a weak link in these installations, as it has about a 6 percent absorption rate. Other potential points of entry can be attributed to bad caulking, overly wide joints, insufficient waterproofing on the interior wall, interstitial voids or water ledges and ice ledges.
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Installing cavity weep system EMC 3639.
"Thin stone veneer's popularity has risen just within the last decade, so many long term effects with moisture in walls have yet to surface," Schultz said.
The Rocky Mountain Masonry Institute stated in its "Adhered Natural Stone Veneer Guide" that there are some instances where adding sealants may also help the wall resist moisture penetration as well as staining. The Institute advises application to areas that are prone to constant wetting, such as the base of walls, sills and caps. Ideally these products will help the veneer surface shed water, while allowing some of the water vapor from within the wall to escape.
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Overlapping sections.
Cavity Wall System
Barrier systems are not 100-percent effective at the start, and over time the material used to seal the joints can break down. You will eventually get breaches in that barrier. The cavity wall was introduced into buildings as a secondary protective measure because it is one of the most effective of all damp precautions — water cannot travel across a void. Most masonry assemblies are permeable to some degree, and sooner or later, especially with weak or incorrectly constructed joints, that masonry will let in water. Without a barrier of some kind, there is a chance that water will work its way indoors, however thick the wall. By inserting a clear cavity, that potential is significantly reduced.
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Installing wall opening weeps.
The concept is to also manage water that may penetrate the outside wall. Any water that gets inside drops to the bottom of the wall where it is collected and evacuated. Essentially it is based on using flashing and some kind of waterproofing membrane or system that's applied to the interior wall. There's a vertical waterproofing component on the wall and a horizontal component, the flashing, which directs water out of the building.
Methods of collecting and evacuating that water vary.
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Attaching metal lath.
"Cotton rope weeps permit capillary action to draw some of the water out of the wall as well as providing a pathway with less resistance to drain any water building up in the cavity," Peterson said. "Open head weeps permit the water to drain out freely and also permit some air circulation into the cavity to dry it out, especially when used in conjunction with vents; however, they can also allow insects and additional water to infiltrate into the wall as well."
Thin Stone Drainage Systems
Though open cavities may be suitable for full-sized stone and full veneer, they are impractical for natural thin veneer installations, which are applied directly to a wall. Products such as MTI's Sure Cavity and Buechel's EMC-3639 systems provide the necessary separation between the thin stone veneer and the structural backup walls.
Rain Screens:
An Open Approach to Water Control
Though rain screen systems aren't used with split-face stone, they present an interesting alternative for hand set, truss set and panelized systems for commercial buildings that utilize 1-3/16 inch thick granite, marble or two-inch thick limestone. It's a frequently used solution in Europe, but U.S. designers generally haven't bought into this technology yet.
"The rain screen system is the next evolution beyond the cavity system," said Michael J. Scheffler, senior consultant for Wiss, Janney and Elstner Associates. "It essentially does away with the exterior barrier — you don't seal the outside joints,"
Rain screens rely on air pressure and the backup wall to prevent water from getting in the building. "Essentially, if you create an airtight and watertight seal in your backup wall, then the air that's blowing against the wall ends up having equal pressure on the panel," Scheffler said. "If you think about water running down the wall when it rains, something has to make the water go across the joint to get to the back side of the panel. If you can equalize the pressure across the joint, so there is no difference, water just keeps running straight down — it won't go into the joint."
The rain screen approach assumes that little water will get into the joints, but if some does get in, the primary barrier is behind the stone. An added advantage is low maintenance — joint sealant doesn't need to be repaired, and the backup wall is protected from the environment, so it's not exposed to any elements that will degrade it.
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"When you install it, you start with a vapor barrier of #15 felt and then you put the weep system over it — a piece of plastic with 3/16-inch corrugated channels," Schultz said. "There's a polypropylene fabric over the top of that, which allows water to get into those channels and drain, but keeps mortar from getting into those channels. You put the metal lath over that, add a scratch coat, and install the stone over top."
The corrugated drainage plane creates a percolation system that allows moisture that may enter from the exterior or condensation that may accumulate from the interior to travel downward toward weeps that are installed at the base of the wall. The water is then directed out and away from the wall, allowing it to vent properly and reducing the chance of mold and mildew growth.
"A predictable drainage plane in any wall system just makes good sense," Koester said. "If water gets in, the amount of time that the water spends in the wall is just as critical as the amount of water. People say they have weeps in the wall, but if the water never gets to the weeps, what difference does it make whether you have them or not?"
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Application of scratch coat.
Best Practices
All wall construction has the potential to get water inside. Good installation practices start from the inner wall out.
"If there's going to be a problem, it starts with the moisture-resistant barrier," said Steve Erickson of Robinson Brick Company. "It must be lapped correctly, have no holes or tears, and the flashing around the windows and base of the wall must be done correctly. If there's going to be penetration of water, more often than not, it starts with these problems."
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Installing thin stone veneer.
Current standards, such as the 1997 Uniform Building Code (UBC) and the 2003 International Building Code (IBC), only specifically address weather resistive barriers and a means to drain water; however, to remain cost competitive, some have chosen to follow the minimum standards and have been slow to add weep systems to their water control strategies.
But Erickson and Koester agree that, despite the added costs, a drainage plane, along with properly installed moisture barriers, will become standard practice for thin stone veneer in the next year or two.
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Cutting off excess wall opening weep.
Installation steps for Buechel EMC 3639 on natural thin veneer project.
Photos courtesy of Buechel Stone
Moisture can now run down and away from wall.
"The industry would win big by putting a separation barrier between the two — one that has the capabilities of getting water from a high point to a low point quickly and out the wall using weeps — and I believe most companies will eventually offer one of their own or from another supplier," Koester said.
References
Wiss, Janey, Elstner Associates Inc.
Northbrook, Ill.
(847) 272-7400
www.wje.com
Whitlock, Dalrymple, Poston and Associates Inc.
Manassas, Va.
(703) 257-9280
www.wdpa.com
Robinson Brick Company/Robinson Rock
Denver, Colo.
(303) 783-3000
www.robinsonbrick.com
Masonry Technology, Inc.
Cresco, Iowa
(536) 547-1122
www.masonrytechnology.com
Buechel Stone Corp.
Chilton, Wis.
(920) 849-9361
www.buechelstone.com
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