OctOber 2016

Technical Brief 09

In almost every case there are two test results that stand out:

• AStM c794 – Standard Test Method for Adhesion-in-Peel This will provide results about the adhesive quality of the sealant. It is important to mention that this test is performed against a coated aluminum substrate and will provide a consistent measurement compared to all sealants tested. Some manufacturers provide C794 test results against various substrates to publish a more comprehensive conclusion as to their sealants bonding capability.

• AStM c719 – Adhesion and Cohesion Under Cyclic Movement 719 results will assign a movement capability to the sealant, which defines its capacity to move within the joint structure. These classifications are noted as 12.5%, 25%, 35%, 50% and 50/100 %. The higher the classification the greater the capacity for movement.

• A third test result that should be considered, but is not found on the C920 list, is AStM D412 – Tensile Set testing. This will award a value to the elongation and tensile strength of the sealant, disclosing a quality of flexibility.

It is important to note that when comparing between ASTM C719 and C794 that you should look for a balance between the movement and adhesion. You may be looking for a sealant that has the highest movement capability but that sealant may not provide the best bond strength. There needs to be a harmony between movement and adhesion. If the sealant will not stick to the surface of the joint, movement means nothing.

The JHInsite Team James Hardie Building Products www.jhinsite.com

Sealant Selection and Application

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The definition of an “exterior sealant” is a material placed in a joint for the purpose of weatherproofing the building and preventing the passage of water, moisture and air through joints and seams of the structure. While this is exactly what a sealant needs to provide, it is also important to consider how a sealant needs to perform. It must possess elements that have the necessary adhesive, cohesive and pliable properties to maintain a reliable seal. This plays into making the right sealant choice to ensure the building is “weatherproof.” When it comes to weatherproofing a building, sealant choice is the first consideration. The second consideration is application. This article will cover these aspects when it comes to sealants and exterior weather sealing applications.

ICC code changes in the last 15 years, in both commercial and residential building sectors, are driving airtight envelope design which not only require sealants to improve this performance but, as a duel use, the sealant must protect the envelope for longevity and durability. The IBC, IRC and IECC all have specific language to address the need for a balance between airtight energy efficient performance and durable wall design. With these requirements in place and sealants as an essential product to ensure the outcome for this performance, the correct product choice and valid application is critical.

As said earlier, when it comes to sealant selection for exterior applications there are two factors that must be incorporated into choice: sealant and application. The sealant, its type, tested performance and distinctive formulation should all be considered and researched before making a final decision. The type of sealant (i.e., modified acrylics, polyurethane, silicone, butyl, hybrid technologies, etc.), are recognized for use in weather seal applications. These types have specific features and benefits but should be scrutinized so that we understand not only the beneficial traits but also their limitations when measuring the demand and variations that the joint design and sealant applications will require. The next consideration in sealant product choice is the tested performance. Sealants are separated into two categories, ASTM C834 or C920. ASTM C920 sealants are more commonly used for exterior applications. Sealants under this category are exposed to 11 lab test methods. These tests are performed to evaluate the sealant and its ability to pass testing standards and requirements set by ASTM. Depending on the applications used on a project, some or all of these test results should be explored. You can find the results of these tests on the sealant manufacturer’s Technical Data Sheet that should be available online.

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• Control: A control joint is formed when two similar or dissimilar materials meet or when substrates do not form a right angle. This joint will require both a backer rod and sealant for proper application. This joint can be as wide as 1” inch and be prone to extreme movement; a highly flexible sealant is necessary for a reliable seal with this application.

• Bedding: For bedding joints, it is especially important that the sealant is of the right consistency and made up of 100% solids so it will not shrink after cure, unlike solvent and latex based sealants that shrink and create gaps after curing.

There are other things to consider, depending on the application, when it comes to a sealant’s performance such as, temperature application, shrinkage after cure, skin over time, paintability and UV exposure and color endurance. These all play a part, not only in the aesthetics of some joint applications but also in the performance and preservation of the joint structure.

The last factor in deciding on a product is the distinctive formulation that the sealant possesses. This identifies the sealant and is the reason no one sealant formulation is the same. Not only do the types separate the use and application aspect of the sealant but also some distinctive technologies within the formulation will allow the sealant to offer very specific and broad variations of use and application. To validate this overall performance against the wide range of joint applications in the industry, manufacturers will test their sealants technology through rigorous methods and procedures. When this information is published it helps to communicate the distinct differences that a specific sealant has and to differentiate it from other sealant formulations.

Validate Sealant through Field testingThe last factor is sealant application. There are two aspects to sealant application that must be considered, joint design and applying the sealant to the joint. Joint design encompasses both the joint type and the materials that form the joint. The joint design consists of three types, fillet, control and bedding which are described below.

Joint types• Fillet: A fillet joint is formed when two surfaces come together

to form a right angle. The sealant used to join these two surfaces is triangular in shape. The sealant must adhere to the variety of substrates you are faced with. Without strong adhesion there is a high chance that the sealant will pull away from the substrate allowing for air and water infiltration.

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The JHInsite Team James Hardie Building Products www.jhinsite.com

The materials that form the joint can impact joint performance. So, it is as critical to evaluate and scrutinize the materials that are applied to a joint as it is the sealant. The first consideration is the movement between materials. Two dissimilar materials, their composition and reaction to changing weather conditions will need to be calculated. The second consideration is the surfaces or substrates of the material that the sealant will be in contact with. The third consideration is any coatings that are applied to the material substrate either before or after the sealant application. When sealant is applied to these materials, all three of these elements need to be addressed and evaluated regarding adhesion, movement, flexibility and compatibility.

It is recommended, but should be required, to field test all joints. The joint surface is prepared for application. The joint should be examined for any abnormalities that would compromise the field test. Sealant is applied to the joint and given the specified period of time for cure. The sealant is then cut and peeled from the joint to analyze performance.

Make certain that you know the performance specifications of the sealant and the conditions in which it can be applied. Some of the items that should be considered are, surface temperature of the material, air temperature, surface moisture or moisture content of the joint material.

Surface preparation is also a significant aspect when applying sealant. A clean surface, free of dust, dirt, oil, grease and other contaminants will ensure a reliable bond and performance.

When applying sealant, continuous contact to the material surface and the correct amount of sealant to “fill” the joint are critical for a durable weather seal. When dispensing the sealant from the gun, the pressure applied, sealant release and speed are the focus. The amount of sealant being released from the cartridge, the pressure of the nozzle against the surface and the motion over the joint need to be balanced. Taking into account the variations between surfaces, joint size and design, can be challenging but through concentration, patience and experience this can be achieved. The last point to mention is tooling sealant. Tooling sealant is recommended to ensure contact to surfaces and remove air pockets. Caution should be taken when tooling a sealant joint. The minimum required depth of the fillet or control joint is ¼” (some joints will require deeper dimensions). This depth is important so that the correct volume is maintained for reliable performance. If the required volume of sealant is reduced by tooling, the joint will be compromised and failure may occur.

Weather sealing a building today takes great consideration to all aspects of the building envelope. The materials that are used to assemble the wall system for structure, thermal, air and moisture barriers and exterior claddings must be integrated to provide optimum energy efficiency and durability. Sealants are the insurance to this integration. If thoughtful and prudent consideration is exercised when selecting the sealant, contemplating joint design and instituting best practice applications, this insurance will provide reliable, long lasting results.

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IMPORTANT: Failure to install and finish James Hardie products in accordance with applicable building codes and James Hardie written application instructions may affect system performance, violate local building codes, void the product-only warranty and lead to personal injury.

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After all we have discussed, do not discount the importance of applying sealant to a joint. This is the final step and without careful application could be the reason for failure to an otherwise perfect weather seal. This is so important that ASTM has developed a 33-page document committed to sealant joints and application, titled C1193. ASTM C1193 can equip contractors, installers and architects with a wealth of information that will provide direction for joint design, surface preparation, sealant use and clean up.

In brief, there are two main topics that branch off to sub-items that we will consider for applying sealant: conditions that are present during application and applying the sealant to the joint.

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