ENVELOPE SYSTEMS/EIFS
Other Considerations in Panel Joints
Additional guidance on the design of joints for good air and water tightness performance through
the consideration of the following factors is provided in Williams and Williams.:
Thermal Movement
Based on the investigation of joint sealant failures, Williams and Williams believe that joint
movement is often greater than anticipated. One factor is that coefficients of thermal linear
expansion are seldom available for EIFS claddings. Also, the color of the cladding is not always
properly taken into account. They therefore recommend that joints be designed to be 4 times the
anticipated degree of movement.
Joint Sealants
As is the general case with sealant joints (see section Design/Sealants), a width to depth ratio of 2
to 1 and closed-cell backup rods are recommended. In applying the sealant, care must be taken to
avoid puncturing the backup rod to prevent "outgassing" and the associated problems of gas
bubbles in the sealant. As mentioned earlier, low modulus sealants are recommended since they
will apply less stress to the base coat bond.
Backwrapping
At all exposed edges of the insulation board, the base coat and reinforcing mesh should be
returned from the system face, over the edge and around the back of the insulation board. Neither
the mesh nor the insulation should ever be exposed to the elements. Such backwrapping reduces
moisture intrusion into the EIFS layers.
Construction Technique
Prior to the application of sealants, all surfaces should be clean, dry and free of particles. Sealant
mixing and priming instructions should be followed closely in the field, with no substitutions.
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