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Performance evaluation of exterior insulation and finish systems (EIFS)
Nabhan, F.
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Pe rform a nc e e va lua t ion of e x t e rior insula t ion a nd finish syst e m s
(EI FS)
N R C C - 4 1 0 6 9
N a b h a n , F .
M a r c h 1 9 9 7
A version of this document is published in / Une version de ce document se trouve dans:
Construction Canada, 39, (2), Mar/Apr, pp. 38-40, 42, March 01, 1997
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rac-crac
Construction Technology Series
A series of technical articles on construction technologv and related subjects attributed
to research and development activities at NRC's Institute for Research in Construction
components has a clearly defined function such as mechanical support (strength and rigidity), reduction of heat fiow, bonding (adhesion), resistanceto
crack initiation, resistance to water
ingress, and surface texture and
appearance.
EIFS cladding exists in two types, Polymer Based (PBI and Poiymer Modtned (PM) systems_ The components of the two systems are iargely identical. except
ADHESIVE
---+7
SUBSTRATE--->-r'S
System Description
REINFORCING FABRIC BASE COAT INSULATION BOARD MECHANICAL ATTACHMENTＭＭＫｾＮＮＭ＾ｩＧｾ FINISH COAT ＭＭＭＭＭｾｾＫＭＭＭＭ｟Ｔ］ｦｯConstruction Canada 97 03
Performance
Evaluation of Exterior
Insulation and Finish
Systems (EIFS)
Figure J. Typical EIFS COallngs
by
Facti
Nabhan
Note: this arllcle is largely drawn from a paper by the same tille wrillen by Mark Bamberg, Joseph Lstiburek and Fadl Nabhan and presented at the Seuenth Conference on Building Science and Technology held March 20 and 21, J997, In Toronto. The technical poper contains more detail on the testing procedures.
Exterior wall assembiies with EIFS contain a substrate (the supporting
system) and a cladding system
composed of an insulation board, a synthetic coating system consisting of one or more layers of a base coat that embeds a suitably treated reinforcing glass-fibre mesh, and a finish coat. The synthetic coating system is commonly
called the lamina. Each of these
When evaluating EIFS, one must consider several parameters that act on the wall system simuitaneously (thermal stress, thermal and moisture driven expansion and contraction, struciural movements, material changes caused by weathering and aging, presence of moisture, etc.l_ The interaction between these factors may provide conditions significantly more severe than those achieved when these parameters arc tested separately. Since testing materials to these parameters separately is not representative of field conditions, this paper postulates a new test for the evaluation of EIFS integrity as a more reliable approach to predict field performance_
E
xterior Insulation and FinishSystems (EIFS) can be
constructed as a cladding
system based on either of two
approaches: i) a cladding with a water-management control (rain screen) OrIi) a face-sealed (barrien approach. While the
barrier approach offers economic
advantages and may be successfuIiy used under specific climatic and service conditions. careful consideration must be given to water management performance of the waIi with EIFS, if good cladding performance (including the benefits of thermal insulation) is to be realized during the life of the building.
38
This test involves pre-conditioning of the system under simultaneous exposure to a water vapour gradient and a temperature gradient, foIiowed by exposure to severe conditions of one-sided, uni-directional climatic cycling. The testing and characterization of the constituent materiais (step t) coupled with the full-scale test for EIFS integrity under exposure to climatic cycling istep 2)
will increase confidence in the
performance of proprietary EIFS systems in North America.
, lor sligl1t differences in the thickness of the base coat and the method of attachment. These polymer coatings are to be considered proprietary and may differ In chemlcai composition, with each requiring a separate evaluation (see the example In Figure II,
The rain·barrier created by the EIFS lamina and its support must remain impermeabletowater during its expected service life. The effects of weathering, aging of materials, cracks in the lamina, and the possible deterioration of the wall substrate must be considered in the evaluation, Therefore, to evaluate the performance of the wall system, one must evaluate not only its initial performance hut also its long·term performance under service conditions.
Issues in Moisture Management of
EIFS Cladding
Although there are many examples of satisfactory long·term performance of EIFS, many failures have occurred as well,
notably failures of the substrate with rainwater penetrating through the lamina, joints and junctions, and trapping moisture within the wall system (see original paper for reference).
The central issue in the evaluation of an
EIFS system Is one of moisture
management to ensure system Integrity during many years of adverse climatic conditions, In doing this evaluation, one often faces a dilemma: should EIFS be treated as a component whose suitability
must be assessed by the
architect/designer or should it be treated as a quasi·generic cladding system with a proven field performance, Traditional material testing and performance assessment do not address the long·term performance and durability issues, and learning from construction failures is no longer an acceptabie approach.
For EIFS, as can be said for many other bUilding materials and systems, the importance of proper design and proper installation must be stressed, Of these, the
proper design is more Important Proper design implies a moisture·management system Ihat includes the design of "a second line of defence" under conditions of realistic buHdabHity. Poor installation of a weli·designed wall system typically works much better than a EIFS product with good Inherent properties, installed by a welHrained applicator, but folloWing a bad design (specifically a poor design of details).
The author and his two colleagues (CO· authors of the longer paper) believe that moisture management of the whole system will dictate whether the subsystems (the EIFS cladding) and substrate will perform satisfactorily. Furthermore, the authors estimate that more than 90% of the EIFS faHures could have been avoided by proper design and suitably implemented bUilding site control. If corrective measures are taken by the whole industry and they occur early in the construction process, the rate of EiFS failures can be reduced to a small fraction of the current rate,
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OFFERS A HIGH 'R' VALUE, AIR SEALING PROPERTIES, AIR BARRIER PROPERTIES, 100% ADHESIONml'
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Reader Inquiry Card No, 055
Figure 2. Example Of "Sto Exterior Insuiation and Finish Sgstem" installation in wood frame construction. For more detailed information see CCMC Euaiualion Report no. 12416
inthe CCMC Registry of Product Eualuations
This article distinguishes between a cladding and a waii system. Cladding is a component of the waii and its functional requirements do not have to be as extensive as those of the waii (see: "What Do We Evaluate? The Difference between an Exterior Wall and Cladding," Construction Canada, Vol. 38, NO.6, pp. 16·191. Often exterior ciadding Is defined as described in the 1995 National Buiidlng Code of Canada: "those components of a building which are exposed to the outdoor environment and are intended to provide protection against Wind, water and vapour."
The exterior face, and in particular the
cladding, need not be the only
components provided to control moisture entry from the outside, If the wall is designed using multiple lines of defence
(see: "Building Envelope and
Environmental Control. Part 3 - Issues of Systems Integration, "Construction Canada, Vol. 35, NO.5, p. 48). For instance, rain is permitted to pass through the "cladding skin" in some cladding
designs, such as rainscreen, pressure
equalized rainscreen (PER) or drain·screen designs. Ir@these cases, drainage of water is provided by a drainage plane or a drainage piane coupled with an air space behind the cladding. If the air space has sufficient venting to the exterior to equalize the pressure difference between the exterior and the cavity (for instance, over 80% of long·term ("steady state") and
50% of transienr wind conditions witl1 a
frequency of 2 Hz or less), the design may be classified as a PER design.
In the barrier waii (face·sealed) approach, however, the exterior face is the only means to control rain entry. The cladding, usually covering most of the exterior face,
needs to provide such means. AS
discussed later, a significant aspect of the test effort is to ascertain whether it will be possible to control rain transfer through the EtFS lamina. Yet, the exterior face of a wall also includes windows and doors
and other penetralions, All these
penetrations and junctions must be equally impermeable to water, if the barrier wall approach is to work.
40
Slructural Framing Sheathing 510 Insulation Board Sio Base Coat Sio Mesh Sio Finish
flexyl and mash at the opening below the Window, overlapping the Flexyllhet covers the shealhirlg.
Slope the il1sulalion to ensure drainage.
A detailed EiFS system based on a face· sealed approach with a waterproofing coating as the 'secondary line of defence' is shown In Figure 2. The waterproofing is intended to protect the iniernal structural elements of the building from moisture ingress. The EIFS cladding system itself, however, will have to resist the resulting forces from any moisture ingress that becomes stored within the system.
In many face·sealed cladding systems, the joint sealant Is found to be the culprit when failures occur. As a result, in Canada, unlike in the United States, most experienced designers do not rely on sealants as the long·term measure for controlling rain penetration. Other solutions, such as drainabie joints, two· stage design with sealant on the backer rod and foam, and the use of expandable gaskets and sealants together are the
norm.
Careful examination reveals that many laboratory test methods were developed to determine material properties; they do not describe the performance of a typical system, Moreover, sysiem performance
under certain service and climatic
Complete perimeter seal required between penetrations and Sio Flexyl.
Weather barrier tape covers Flexyl at joint in substrate. Tape laps 25 mm (''') onlo face 01 well.
Sio Flexyl& Mesh Installed continuously
ovel substrate and
arOLJnd framing at penetralions.
conditions may substantially differ from that defined for a typical "performance" test.
Nonetheless, a 'great deal has been learned from the testing of moisture performance of the lamina. The thickness of the base coat has a critical effect JUSt as composition, porosity and aggregate size have. Componenl material testing must be coupled With 'system' performance to obtain a more complete asessment.
system Performance Evaluation:
More than Considering
Constituent Materials
One could estimate the probability of moisture coming through the EtFS lamina and through Joints, assess the damage potential for this moisture and attempt by means of. smail·scale tests to make Sure that no significant moisiure damage occurs. Nevertheless, since one has little control over the various trades involved in the wail conslruction, one must consider Ihe worst scenario, i.e, that Water wiil find its way Into the wall, and deal with that. This would imply incorporating into the design a drainage plane and a second line of defence to protect adjacent substrates and structurai elements. What remains to
be assessed IS the integrity of the EIFS when subjected to an ingress of moisture.
concept of the Test for EIFS Integrity
One of the parameters affecting the integrity of a cladding system is moisture entrapment. The integrity test should therefore involve conditions representive of field exposure that lead to moisture entrapment. Under field conditions, the freeze-thaw temperature cycles act only on one side of the material. Exposing a dry specimen to conditions of one-sided, uni-directional climatic cycling wouid gradually increase its moisture content to a critical level when a "failure" might occur. (At a specific number of cycles that would correspond to the critical moisture content.) Such a test would normally require, however, a very long period of exposure_ After all, most moisture damage usually occurs after many years of exposure.
In a cold climate, where a uni-directional heat flow prevails during the winter period, moisture flows toward the cold side, resulting in zones of low moisture content on the warm side and high moisture content on the cold side, (Whether this zone is located at the cold surface of the specimen or at some distance from the cold surface depends on the nature of the surface layer, periodic and daily oscillation of the outdoor temperature as well as drying ability of the flnish coat)_
To achieve moisture content that may
be near the critical moisture content for freeze-thaw before initiating the actual integrity test, a 28-day pre-conditioning
procedure is used_ During
pre-conditioning, EIFS specimens form a
divider between two environments;
• 24±2'C with 90±5%RH, representing the room (wann) side, and
• -1O±2'C, with ambient RH, representing the weather (cold) side.
Moisture moves because the thermal gradient creates a strong driving force. (A constant thermal gradient has been
42
shown to be one of the most effective methods to achieve a moisture saturation in closed·cell cellular plastics). A
simultaneous exposure to water vapour
concentration and temperature gradients
causes accumulation of moisture in the
EIFS specimens. How much moisture could be accumulated in the EIFS specimens during the pre-conditioning period depends on the hygrothermal properties of the constituent materials. tf the EtFS lamina, which are placed on the cold side of the assembly, do not permit a sufficient flow· through of moisture, there may be more moisture accumulated in the specimen.
Starting the integrity test after the moisture content of the EIFS has been significantly increased during the pre· conditioning period reduces the number of climatic cycles required for the integrity test itself. In contrast to the pre· conditioning procedure involving a constant temperature gradient, the integrity test employs cycling on the weather side (one-sided cycling). The specimen is placed between the two environments and one of them is cycied over 20 days (40 cycles):
• constant warm side with temperature rising to 30±2'C, and relative humidity 90% RH; and
the weather side, chamber temperature varies between -20±2'C (cold period) and t5±3'C (warm period) at ambient RH,
During the integrity test, conditions on the inner surface are kept constant. The air temperature on the outer surface of the warm side is 30±2'C and water (with a temperature 15±5'C) is sprayed on the weather surface of the specimen. This action increases the moisture content of the surface, and if the specimen surface is cracked or if it is prone to hygroscopic/ capillary moisture actions, it will likely increase the moisture content within the specimen of the system. Oscillating temperatures on one side of the specimen
cause moisture movements back and
forth within the inner parts of the EIFS specimen, Because of differences in
moisture transmission properties of the different layers, there would be moisture accumulation at some interfaces. To
determine whether this moisture
accumulation, alone or in conjunction
with other climatic factors, causes any detrimental effect (delamination, cracking. blistering or sagging), is an objective of this test.
The purpose of the integrity test is to assist the designer in evaluating the water management performance of the Whole system. Therefore, the test panel should include the same substrate as that used in fleld appiications, typical fenestration such as vinyl windows (the highest coefficient of expansion), decorative frames (if used), wall penetrations, the window flashing and at least one expansion joint.
The level of moisture entrapment achieved during the pre-conditioning stage depends on the hygrothermai performance of all EIFS layers: the substrate, the thermal insulation and the lamina. To examine the effect of the finishing coat, it is recommended that a part of the test specimen be provided with the base coat only, i.e, no flnishing coat is applied. It is also recommended that a vertical joint between two substrates be located in the centre of the test specimen. tn conclusion, it is believed that small-scale tests on EtFS lamina characterizing the constituent materials, combined with iarge-scale representative "system" testing, is the best way to assist the designer in predicting the moisture performance of the building envelope.•:.
Pad; Nabhan
is a product eualuation Officerin the National Research CouncU's Institute for ResearchinConstruction. He isa member Of the Institute's Canadian Construction Materials centre, which carries out eualuations of innouatiueconstruction products. For more
information or to obtain a copy of the longer technical pape" he maybereached at: Tel (613) 993·7702; e-mail at: fadi. nahban@nrc.co.
