Control joints in EIFS are critical for managing thermal movement and preventing cracking in the finish coat. This article outlines spacing, joint construction, sealant detailing, and best practices for EIFS assemblies.
Why Control Joints Are Required
EIFS systems experience significant dimensional changes due to temperature and moisture fluctuations. Control joints prevent cracking in the base coat and finish layers and isolate movement between structural components, floors, and penetrations. Manufacturer installation instructions and ASTM E2486 require control joints at key locations.
Joint Spacing and Layout
- Horizontal joints at floor lines or slab edges
- Vertical joints at structural columns, dissimilar substrates, or building step-backs
- Maximum uninterrupted panel sizes: typically 144 ft² with a max dimension of 25 feet
- Joints at window corners and changes in wall height or geometry
Joint Construction and Backer Material
Joints must be continuous through the foam insulation and reinforced base coat. Use closed cell backer rod and a Class 25–50 movement-rated sealant. Plastic or PVC control joint accessories may be embedded at joint edges to create a clean finish. Sealant must adhere to primed EIFS base coat and remain flexible over time.
Common Mistakes to Avoid
- Omitting joints at floor lines or dissimilar framing
- Improper sealant joint geometry or lack of backer rod
- Sealants applied over dusty or unprimed base coats
- Failure to reinforce base coat mesh around joint edges
Perform adhesion testing in field mockups and verify control joint alignment with architectural elevations. Joints should not interrupt water management or WRB continuity behind the foam insulation.
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