Traditional masonry stucco is one of the most durable exterior wall claddings available and modern synthetic stucco offers outstanding insulating properties. Both will last for years without repairs if you manage water properly. Both will fail if you don’t.
What is Stucco?
Before we jump into water management we should take a quick detour into the world of stucco. What is it and how is it installed?
Traditional Masonry Stucco
Masonry stucco is a cementitious wall cladding that is mechanically fastened to the exterior wall of a building.
The installation of masonry stucco can be broken into four steps:
- attaching a water resistant barrier (WRB) to the exterior sheathing of the building
- self-firring expanded metal lathe is then mechanically fastened to this substrate using nails or screws
- metal casing beads are installed at window openings and the tops and bottoms of walls to allow for water drainage and help to establish a consistent depth for the finished wall cladding
- masonry is then applied to the wall in 3 layers: an initial “scratch coat”, a second “brown coat” and a final finish coat.
Portland cement is the best cement to use for installing modern masonry stucco Older homes may have been built using lime cement that was mixed on site by the plasterer. Older homes also frequently feature wooden firring strips between the WRB and metal lathe and often lack casing beads.
Modern Synthetic Stucco
Modern stucco systems are based on a system of exterior wall cladding developed in Germany after the Second World War. Germany was rebuilding after the tremendous destruction of the war. They developed a stucco system that was rapid to install and provided insulation to the exterior of the building. The system is known as the Exterior Insulation and Finish Systems (EIFS).
EIFS consists of a water resistant barrier (WRB) over the sheathing of the building (usually plywood or OSB in residential construction). Expanded polyethylene (EPS) foam sheets are applied over the WRB and covered with a thin layer of fiberglass mesh embedded in acrylic masonry basecoat. A sanded acrylic finish coat is applied over the basecoat, sealing the system from exterior moisture and protecting it from UV.
There are a broad range of approved installation practices for modern synthetic stucco, but all of them include a drain plane behind the EPS foam to allow moisture to exit the system at weeps.
Older EIFS installations may not feature a drain plane behind the EPS sheets and can be more prone to moisture damage, particularly if proper weep areas have not been installed around window and door penetrations and at the base of walls.
Stucco Water Instrusion- What Does the Water Do?
One thing that you’ll notice about the description of both masonry stucco and EIFS is the need for a water resistant barrier under the stucco and an emphasis on design and installation that allows any water that enters the system to rapidly drain to the exterior of the wall. The reason for this is simple: water trapped in the wall will destroy stucco.
If water gets behind your masonry stucco, several things will happen:
- It will begin to corrode the wire lath and fasteners that hold the cladding to the wall. Over time, cycles of freeze and thaw will work the stucco loose from the sheathing and form bubbles and cracks in the wall surface.
- Failure of the water resistant barrier behind masonry stucco can lead to rot and deterioration of the wall sheathing that the wire lath and fasteners are attached to, resulting in detachment of the wall cladding from the sheathing.
- With older lime stucco installations water can degrade the stucco itself, washing the lime out of the cement so that the wall consists mainly of sand. You can put your hand into a stucco wall that’s deteriorated this way and pull out chunks of sandy debris.
If water gets behind your EIFS wall it is likely to rot the wall sheathing, particularly in older EIFS insulations that may not have featured a WRB. Standards for EIFS installations have developed over time and homes built twenty or more years ago may not be up to current practices. Older EIFS homes may not have been built with a WRB or even sheathing at all. Water inside such a wall can do extensive damage.
Modern installation practices create outlets for water that enters the wall system to exit. Older homes may not have these design features. In an older EIFS home, it makes sense to consider improvements to water management outside the wall cladding system. This can prevent damage to the interior of the wall by controlling moisture before it enters that stucco wall system. Upgrading flashings and improving bulk water management with effective gutters are cost effective solutions to mitigating water damage in a stucco homes..
A stucco wall that has been damaged severely requires major surgery. Damaged areas need to be cut away with a grinder. Rotten sheathing is replaced. Structural damage is assessed and repaired as necessary. Then the entire system needs to be rebuilt starting with a proper WRB and progressing outward with either masonry or EIFS installation. It’s an expensive and time consuming process that is best avoided. It is far more cost effective to prevent water damage to stucco walls than it is to repair them after the fact.
Here are four key areas to focus on to help effectively manage water and prevent it from damaging your stucco.
Install Kickout Flashings
Kickout or kick flashings are a key component to effective water management. These angled flashings, placed where a roof line meets a vertical wall, direct water away from the wall and out toward the gutters. Without kick flashings, water will run down the vertical wall where the roof meets that structure. Over time water will wick into the exterior wall and begin to degrade the stucco. Kick flashings are inexpensive insurance and can prevent expensive repairs down the road.
Get Good Gutters
Gutters are an often overlooked area of weakness when it comes to stucco. There are two major problems that can form around gutters.
- The first comes from improperly pitched or clogged gutter systems. These can allow water to pool in areas of vulnerability and enter the wall system over time. Poorly pitched and draining gutters can also exacerbate problems with ice dams in cold conditions.
- The second major issue with gutters has to do with penetrations through the exterior wall.Water leaking through stucco walls can sometimes be the result of downspout brackets that were installed improperly. Attaching downspouts requires drilling penetrations in the stucco cladding. These penetrations must be properly sheathed and waterproofed to ensure that water will not wick into the interior wall should gutters become clogged. A blob of silicone caulk is not proper waterproofing. Qualified gutter installation professionals know the right procedures for properly installing hardware to prevent water ingress at penetrations.
- To get the most benefit from improvements to gutters, they must be paired with proper flashings. These components act in concert to move bulk water away from vulnerable areas.
Prevent Ice Dams
In cold climates, ice dams can form at the edge of roofs when attics are improperly insulated and vented. Repeated freeze/thaw cycles can force water up under shingles and onto the roof deck. This water can then pass into the interior of the building or the interior of stucco walls and create extensive damage. It’s essential that attic spaces are properly insulated and vented. When shingle roofs are replaced the lower edge of the roof should be protected with an adhesive backed waterproof membrane like Ice and Water Shield to mitigate water ingress should ice dams form.
Fix Flat Roofs
Failed EPDM flat roofs are a frequent source of water ingress to stucco walls, particularly if they haven’t been properly pitched. On such a roof water will make its way into areas of vulnerability that may not have been anticipated during the initial design and construction of the building. It is critically important that the roofs are designed and installed so that water can rapidly drain off of the roof deck without passing into interior walls.
Water and Stucco Don’t Mix – Keep the Water Out
Water is the enemy of stucco, both traditional masonry stucco and modern synthetic EFIS systems. Damaged stucco is expensive to repair. Avoid the expense and trouble by taking steps to properly manage water and keep it where it belongs: outside your home.