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News Release from: Emseal Joint Systems | Subject: Choosing a sealant for building applications
Edited by the Buildingtalk Editorial
Team on 22 May 2007
Choosing a sealant for building
applications
Lester Hensley from Emseal explains why joint sealants function as an integral component of the building envelope and is not just a matter of filling the gap.
Lester Hensley, CEO and President, Emseal, on choosing a sealant for building applications Sealing of building components and structural expansion joints is not just a matter of filling the gap
This article was originally published on Buildingtalk on 9 Sep 2008 at 8.00am (UK)
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Joint sealants function as an integral component of the building envelope, protecting the structure from damaging moisture ingress caused by wind, gravity, capillary force, surface tension, and air pressure differentials.
While they only constitute a small percentage of a construction budget, joint sealants and other waterproofing-related issues are responsible for a majority of post-construction complaints and requests for retrofits.
Poorly designed, manufactured or installed joint sealants often need to be replaced in as few as two to five years after construction, at a considerable cost to stakeholders.
Further reading
Emseal introduces breakthrough 'DSM System'
Watertightness, low-temp flexibility and high-temp stability in structural movement joint sealing from Emseal.
Emseal innovative double-sided joint seal
Seismic Colorseal-DS seals inside and outside of structural joints in buildings in single installation step.
Emseal revolutionary Seismic Joint System
Emseal Seismic Joint System is ideal for use in applications requiring watertight, sound dampened seismic and large movement joints, such as in parking decks, stadiums, and floors. .
According to CIRIA (Construction Industry Research and Information Association), the treatment of movement joint gaps in buildings, from design, technology and installation standpoints, is grossly under-emphasized: "Although they are a minor component of the building envelope, joints with sealants are often responsible for defects and failures--sometimes after only a couple of years." Additionally, the overall energy efficiency of a building is highly dependent on the ability of joint sealants to provide thermal insulation and a barrier against air infiltration.
As Tom Kuckhahn pointed out in "Exterior Wall Systems, R-Value, and Revenue" in the September 2003 issue of Construction Specifier: "[heat] seeks the path of least resistance, so the R-value of an actual wall is closer to the R-value of the least insulating portion of that wall".
All too often, the joint sealant represents that least insulating component, thereby significantly degrading the effective R-value (measure of thermal resistance) of the entire wall system.
Sealant Options: Liquid, Impregnated Foam and Hybrid.
The waterproofing industry has many product options for joint sealing, among the most common offerings are liquid sealants, impregnated-foam sealants and hybrid technology sealants.
Liquid Sealants.
Liquid sealants are widely used because of the relatively low material cost and the speed of installation.
Architects appreciate the wide color range that is available.
Liquid sealants, particularly high-performance silicone sealants, provide moisture impermeability, low modulus, UV resistance and the ability to retain these physical properties with changes in age and temperature.
Liquid sealants are supplied in tubes, pails, sausages, or in other ways convenient for shipping.
They are extruded through a nozzle into joint-gaps over a pre-placed foam backer rod.
The installer then tools the sealant against the backer rod to achieve the "hour-glass" cross-sectional shape needed for handling extension and compression movement.
The achievement of this "hour-glass" shape is critical to the performance of the liquid sealant once it has cured into a solid plastic state.
Tensile Stresses.
In the world of adhesives (into which liquid building sealants fall), a fundamental concept is that adhesives are at their best when used in conditions where the basic stresses in the material are shear stresses and not tensile stresses.
The best of all worlds is the elimination or virtual elimination of any tensile stresses at either the bond line or within the elastomer.
A limitation of liquid sealants is the presence of tensile stresses at the bond line and within the body of the cured sealant during extension movement.
The negative effect of these tensile stresses is aggravated by installation of the liquid sealant in other than the specifically required geometry.
Furthermore, liquid sealant failure has been proved to be accelerated by cycles of compressive stress (when the joint is closing) followed by cycles of tensile stress.
Unfortunately, it is notoriously difficult to consistently achieve the required geometry.
The Sealant Waterproofing and Restoration Institute (SWRI) specifies a 7-12 step installation process required in order for liquid sealants to function properly.
Deviations in the depth of the backer rod, for example, can cause the sealant to fail completely.
As redundant or two-stage sealing using the, so called, "double caulk-and-backer rod" detail has gained popularity, achievement of a clean substrate and installation to the required geometry in the second seal deep inside the wall section is extraordinarily difficult to achieve.
Impregnated Foam Sealants.
Another common method of sealing expansion joints is the insertion of preformed, impregnated, foam sealants.
They are produced by partially filling the cells of high quality cellular polyurethane foam with non-drying, water-repelling adhesive agents.
The combination of this impregnation treatment followed by compression creates a sealant material that is always in compression.
Preformed sealants, in contrast to liquid sealants, are supplied ready for installation in their finished, functional state.
The principal advantage of preformed, precompressed, impregnated foam sealants is that they provide thermal insulation in addition to moisture impermeability.
R-Values of as much as 3.28 per inch of depth are typical of impregnated foam sealants.
This means that on a typical 3-inch 75mm) joint, the R-value at the structural joint gap of a wall sealed with an impregnated foam sealant is 3.28 x 3.5 (the depth of seal of the impregnated foam sealant) or R-11.48.
This compares favorably to a 2 1/2-inch thick exterior-insulated facade (R-4 to 5.6 per inch of thickness) as well as to the R-value (around R-12) of a typical insulated precast panel.
Preformed impregnated foam sealants, by virtue of their depth, density, and adhesive-infused cellular composition, also resist air pressure differentials caused by the Bernouli Effect, and/or by the stack effect and/or HVAC loading.
They are easy to install, because they are supplied in a virtually finished functional state.
Sizing and Color.
Impregnated foam sealants require correct sizing to maintain a suitable level of compression for sealing.
Correct sizing is a necessary requirement for all sealing methods.
Liquid sealants are equally dependent on correct sizing, because one cannot install 25mm (1-inch) backer rod into a 40mm (1 1/2") joint-gap, tool liquid sealant over it and expect to achieve the necessary geometry for the sealant to function".
"The color selection of standard impregnated foam sealants, black or gray, is widely incorporated in design to create shadow-line effects".
"However, when the aesthetic effect preferred is to make the material blend or coordinate with the color of a substrate this limited selection becomes an issue".
"Hybrid Sealants Hybridization is defined as the enhancement of positive traits while eliminating or reducing negative traits through the combination of different species, materials, or technologies".
"As the limitations of individual technologies become apparent, hybrids often emerge to create more effective products".
"Such new products preserve the best features of the component materials while eliminating any weaknesses that caused the original technologies to stagnate".
"A Modern-Day Example".
"A modern-day example of where hybridization is succeeding where individual technologies have stalled is in the development of alternative-fuel vehicles".
"Internal combustion engines, in their current form, have a limited long-term future due to inefficiency and negative environmental impact".
"Battery-driven, purely electric vehicles to serve mainstream use are still not viable due to limitations of current battery technology and the hassles of recharging".
"Available on the market in recent years are high-performance vehicles powered by highly efficient internal combustion engines and battery-powered electric motors (working in combination or alone depending on driving conditions)".
"These hybrid vehicles feature a sizeable leap in fuel efficiency and are less polluting".
"Architects and engineers once needed to make trade-offs when specifying joint sealants".
"On one hand, liquid sealants applied in conjunction with a backer rod is a commonly used method that is available in a wide color range and is resists degradation caused by ultraviolet light, but it has a very low R-value and is susceptible to failure due to tensile stresses".
"On the other hand, impregnated foam sealant is just the opposite - it offers a good thermal insulation, but lacks color choice".
"Emergence of Hybrid Sealants".
"In the early 1980s a new "hybrid" solution of sealant technology was invented".
"By combining factory-applied and cured silicone bellows with an impregnated expanded foam sealant backing, hybrid sealants overcome the fatigue and potential cohesion failure of liquid sealants".
"Additionally, when compared to alternatives for structural joint sealing, hybrids provide non-invasive anchoring, eliminating the need to drill or screw into sensitive substrates".
"This removes the risk of spalling and enables installation into inside corners that are impossible to seal with, for example, aluminum rail and rubber strip-seals".
"Hybrid joint sealants provide an optimal solution for many applications including movement joints, large joints over 25mm (1-inch), applications where resilience or the need to resist air-pressure and thermal differentials is essential, and anywhere a structural or new-to-existing gap needs filling and sealing".
"In addition, more recent product developments, juxtaposed against new criteria for durability and energy efficiency driven by the adoption of air-barrier codes and LEEDS criteria, make hybrids for small (starting at as small as 8mm (3/8")) joints increasingly justifiable.
Composition of a Hybrid.
The acrylic-impregnated-foam sealant combined with factory-applied ultra-low modulus silicone liquid sealant in the form of a bellows.
The opening and closing movement of the joint-gap results in the surface sealant folding and unfolding (rather than stretching and compressing) thereby eliminating substrate bond-line stresses and failure or composition changes caused by pre-cure joint-gap movements.
The seal is made by partially factory compressing the foam followed by the application of the silicone.
The silicone coating is applied to a factory-controlled thickness.
It is then cured under controlled conditions free of dirt, temperature change and movement of the substrates during cure.
Once the silicone coating has cured, the material is compressed to an installation dimension comfortably less than the field-measured joint-gap size.
It is held in this pre-compressed state by its packaging until immediately prior to insertion in the intended joint-gap.
Installation Installation of hybrid technology involves removal of the sealant from the hardboard and shrink-wrap packaging that holds it compressed to less than the joint size.
The sealant is inserted joint opening recessed to the desired depth but at least deep enough to accommodate a fillet-bead of sealant applied later.
A pressure-sensitive mounting adhesive on one face holds the material in space while it slowly expands to fill the joint.
A fillet-bead of liquid silicone locks the bellows to the substrate.
The fillet-bead, while field applied, is never in tension as in a conventional liquid-sealant-and-backer-rod installation and is a redundant measure in ensuring that the bellows is sealed to the substrates.
Conclusion.
Choosing the right sealing and waterproofing solution requires the full understanding of the advantages and limitations for each option.
In order to prevent having to replace poorly designed, manufactured or installed joint sealants it is important to select a sealant that preserves the best features of the component materials while removing the weaknesses that limit performance.
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