Stucco Moisture Management

Stucco Moisture Management

Adhered masonry systems such as stucco are economical and beautiful. However, modern stucco wall assemblies behave differently from those constructed 50 years ago.  Newer building materials (like OSB, plastic WRBs) and methods (air sealing, increased insulation, vapor control) have reduced the wall’s drying capacity and in turn increased the rate of failure from entrapped moisture. The portland cement contains surfactants that compromise the water repellence of many WRBs. Creating a continuous, predictable air gap between the scratch coat and the WRB with a rainscreen drainage mat improves the ability of the wall to drain and dry. The air gap enhances the performance of the WRB by eliminating hydrostatic pressure, mitigating risk from fastener penetrations.

Best Practice Detailing for Stucco

  • Predictable and continuous rainscreen drainage gap over the entire wall
  • Rainscreen compatible weep screed to drain the bottom of the wall
  • Ventilation at the top of the wall to increase drying potential

EIFS vs Stucco with Continuous Insulation

The EIFS industry recognizes that continuous rigid insulation is not a perfect barrier system, and as a result relies on a drainage gap between the foam and the water resistive barrier to drain liquid. A 1/8 inch air gap creates a capillary break to drain liquid water and limits thermal loss. Stucco detailing with continuous rigid insulation take cues from EIFS by having an air gap to drain behind the rigid insulation.  A second draining layer immediately behind the stucco is advantageous as well to quickly and evenly dry the stucco, reducing efflorescence and cracking. 

Essential Moisture Management Components for Stucco

Sure Cavity Rainscreen Drainage Plane

Ventilated Rainscreen Air Gap

 Sure Cavity

An air gap prevents hydrostatic pressure in the wall assembly, lets gravity drain liquid moisture, and water vapor to exit at ventilated terminations. Sure Cavity™'s rigid channels and mortar blocking fabric ensure a clear and continuous drainage gap along the entire backup wall. Sure Cavity lays flat on the sheathing to create an even surface for stucco. In the lab and on the jobsite, Sure Cavity rapidly drains and dries walls.

Rainscreen-compatible weep screed

Ventilated Weep Screed

 L & R Weep Screed 

Gravity drains liquid water to the weep screed at the bottom of the wall, and then it needs to escape. The L & R Weep Screed™ from MTI is the only rainscreen compatible weep screed on the market, with large slots for drainage immediately below the Sure Cavity™ rainscreen. The L & R Weep Screed allows you to create a ventilated rain screen assembly for maximum drying power to keep your walls dry and safe for generations. 

Window Sub Sill Drainage

Window Sub Sill Drainage

 Window Drainage Plane

Windows are the most common area for moisture problems because they create an interruption in the WRB & drainage plane.  Window Drainage Plane™ maintains a gap for drainage on sloped window sub-sills to prevent moisture accumulation. 

Moisture Diverter on Drainage Plane

Moisture Diverter Above Openings

 Moisture Diverter

Window rough openings are a common weak spot for moisture problems - but if the rough opening doesn't get wet problems are prevented. The Moisture Diverter™ channels water in the rainscreen drainage plane away from the rough opening to reduce the potential for leaks and keep windows dry. 

Ordering & Expertise

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