Tips for success with exterior insulation and finish systems

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Impact damage that is not repaired promptly provides a pathway for leaks.

Poor workmanship
Sealant joints are a major source of problems with EIFS cladding. Incorrect selection or application of sealant (or sealants missing altogether), provides an easy path for water entry and premature deterioration. Inappropriate sealant may even lead to cohesive failure of the EIFS finish coat. Sealant erroneously applied to the finish coat, rather than to the mesh-reinforced base coat, is a common source of problems.

Missing or incorrectly installed flashings provide a conduit for water infiltration. Door and window openings should incorporate flashings to direct water away from headers and sills. At roof/wall intersections, drip-edge flashings should be installed to channel rain away from the wall face.

Base coat thicknesses that do not meet the manufacturer’s guidelines are another typical source of trouble for EIFS façades. A base coat that is too thin provides insufficient waterproofing protection, whereas a base coat that is too thick may lead to cracking.

Reinforcing mesh that reads through at joint edges or terminations can indicate inadequate coating thickness. Alternatively, the mesh may have been insufficiently embedded in the base coat. Continuing the mesh-reinforced base coat around to the back of the insulation board, known as ‘backwrapping,’ is critical to providing continuous waterproofing protection at edges, penetrations, and terminations. Factory-formed track may be used at foundation terminations instead of backwrapping, when appropriate.

Aesthetic joints (V-grooves) aligning with insulation board joints can lead to cracks as the building moves. Mesh-reinforced base coat should be continuous at recessed features.

Window and door corners, like aesthetic joints, should not align with insulation board joints. ‘Butterfly’ reinforcement, whereby rectangular pieces of reinforcing mesh are laid diagonally at the corners of windows, doorways, and other openings, is important to prevent cracking.

Expansion joints are too often neglected in EIFS construction, but they are no less critical here than with other types of cladding. Expansion joints should be used:

  • at changes in building height;
  • at areas of anticipated movement;
  • at floor lines (particularly for wood-frame construction);
  • where the substrate changes;
  • where prefabricated panels abut one another;
  • at intersections with dissimilar materials; and
  • where expansion joints exist in the substrate or supporting construction.

Insulation board should not bridge expansion joints in masonry or concrete substrates. Instead, an expansion joint should be created in the EIFS insulation over the underlying joint.

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Moisture meters may be used as part of an EIFS failure investigation.

Insulation board should meet the manufacturer’s recommended minimum thickness (usually 19 mm [3⁄4 in.]), even at aesthetic joints and recesses. Vertical joints in the insulation should be staggered in a running bond pattern in successive courses, with boards abutted tightly to one another. Gaps between boards should never be filled with base coat or adhesive, which can cause cracking; rather, slivers of insulation may be wedged between boards where needed. Selecting a board adhesive that is compatible with both the insulation and the substrate is critical to successful performance of EIFS.

Climate factors
A humid climate with limited drying potential can devastate some EIFS assemblies, particularly when the rate of wetting exceeds that of drying. Poor design and installation exacerbate this problem by providing avenues for water to penetrate the cladding while the humidity prevents damp walls from drying out.

The amount of rain deposited on a wall depends not only on climate, but also on the architecture and siting of the structure. Building height, overhangs, exposure, and façade details all affect the path of rainfall, channeling more or less moisture toward the cladding.

Cold climates may also lead to premature failure of the system, particularly when EIFS coatings are applied at temperatures below the manufacturer’s design range.

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3 comments on “Tips for success with exterior insulation and finish systems”

  1. I didn’t know there were so many different types of insulation. I like having different choices so this is great for me! Insulation is a crucial part of building an efficient structure so this will be really helpful.

  2. Great explanation of the different types of insulation available. I had no idea there were so many different kinds so this is really helpful.

  3. I had no idea there was a difference between stucco and exterior insulation and finish systems. I assumed that stucco was the same thing as the insulation board and exterior coating that you are discussing in your article! I’ll be sure to look at my options more carefully when I need some exterior waterproofing done!

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