Tips for success with exterior insulation and finish systems

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To true the wall surface, the installer should level the insulation board, rather than build up base coat.

Impact damage
EIFS consists of a thin, brittle coating over a soft substrate and are easily damaged by impact. Holes, dents, or scrapes can lead to water infiltration, so it is prudent to provide extra reinforcement at susceptible locations.

Areas needing impact protection should use heavy-duty mesh, usually 340 to 566 g (12 to 20 oz), rather than standard 127-g (4.5-oz) mesh. For outside corners, the design professional may specify a heavier corner mesh to guard against excess wear and damage. Intricate decorative elements require a lightweight, flexible detail mesh, which conforms to fine contours and ornamental details while still providing some measure of impact protection.

Building movement
Wood substrates tend to exhibit cross-grain shrinking, along with expansion and contraction from changes in humidity. For concrete, movement tends to come in the form of frame shortening, whereby concrete deforms over time due to shrinkage and creep. Steel structures are not immune to the effects of building movement, particularly at long-span beams, where transverse forces are greatest and deflection is more likely. To prevent irregular cracking, sufficient provision for expansion and control joints should be part of the design.

Unsound substrate
Poor quality control in the production of OSB, a common substrate for EIFS, has raised some concerns about premature failure, so a reputable manufacturer with a good track record should be used. Traditional gypsum board, often used with EIFS, tends to exhibit problems with moisture absorption. It should be avoided in damp or humid climates. Even if the substrate is of high quality and suitable for the building location, failure to correctly specify or install substrate attachment may lead to premature cladding problems.

Catastrophic EIFS failure
In 1995, a task force of the American Institute of Architects (AIA) conducted a survey URL of over 200 homes with a dozen different EIFS systems in Wilmington, North Carolina. Of those homes, 68 percent had incorrect or missing sealant joints and 94 percent experienced water intrusion. Earlier that year, homeowners in New Hanover County, North Carolina filed a class action lawsuit, against multiple EIFS manufacturers. Under the settlement agreement, an EIFS Inspection Protocol was introduced, which involves moisture detection through resistance probe moisture meters and electronic impedance scanning meters. The testing procedures and criteria established in this protocol have become the standard for EIFS failure investigations.

Design considerations
The performance and longevity of any cladding assembly depends on the proper design and installation of the system, and EIFS is no exception. Sequential coordination of work is one way to avoid defects, particularly at intersections and terminations. The general contractor, framers, window installers, sealant contractor, EIFS installer, and other trades should be organized such that the work of one does not adversely impact the work of another. For large areas, sufficient workforce should be on site to permit application without cold joints or staging lines. Whenever possible, EIFS application should proceed on the shaded side of the building.

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For retrofit projects aiming to improve performance and update appearance, EIFS provide a practical option in terms of aesthetics and function.

Sealant joint and flashing design
The design professional is responsible for determining the appropriate size and location of joints, and for specifying a compatible sealant. In general, low-modulus sealants that maintain their properties when exposed to ultraviolet (UV) radiation are recommended for EIFS. Sealant selection should consider anticipated joint movement, substrate material, cyclical movement, and exposure to temperature extremes. To prevent premature degradation at the bond line, closed-cell backer rod should be used in lieu of open-cell, which tends to retain moisture.

At points where water can enter the wall, (e.g. roof/wall intersections, window and door openings, and through-wall penetrations), it should be directed to the exterior with appropriate flashing. Flashing should be integrated with air seals, sealants, rough opening protection, and other waterproofing materials.

Surface texture anomalies
The phenomenon of ‘critical light’ occurs when natural or artificial light strikes a wall surface at an acute angle, less than 15 degrees, such that tiny surface irregularities cast a shadow. To minimize the negative aesthetic impact of critical light, the EIFS installer should remove planar irregularities, high spots, and shallow areas with a high-quality rasp (file with projecting teeth). Mesh overlaps should be feathered to minimize read-through, and a skim of base coat may be applied to blend laps. To correct critical light defects in existing EIFS, the design professional may specify re-skimming of the original finish coat with an appropriate base coat, followed by application of a new finish after the base coat has dried.

Cool weather application
Damage to EIFS components from low-temperature application may be undetectable in the short term, but tends to emerge later as coatings crack, flake, soften, and delaminate. For most acrylic and cementitious coatings, application is restricted to temperatures of 4 C (40 F) and rising. Below the design minimum, these coatings will not develop proper physical and chemical strength, and they may not coalesce correctly to form a film.

When scheduling EIFS installation, one should avoid the times of year when thermal cycling is at its highest such as autumn, when it is warm during the day and cold at night. Materials with controlled set times will set up more slowly in the cold—the project schedule will need to allow additional time for curing between coats. The ambient temperature and the surface temperature of the substrate—
which may be significantly lower—should be considered. It is advisable to warm certain substrates before application.

Patches and repairs to existing EIFS are particularly susceptible to cold-weather cracking, since seasoned material is combined with new material that has not yet developed its full strength. After initial set, patch areas should be kept warm to assist in curing and to reduce thermal stress.

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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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