Case 4

Good Practices

Design

-Sealants must be continuous and of consistent quality.

-Avoid bridging angles, particularly with mastic strip sealants. Apply extra thickness at corners as a precaution.

-Sealants used shall be of suitable type to form a seal against water and air penetration and to withstand stresses during assembly, transportation, installation and operation of the curtain wall system. Sealants displaying predominantly elastic characteristics are recommended such as polysulphides, polyurethanes, silicones or other materials approved by the Specifying Authority.

Construction

-Workmanship on-site should be ensured so that good designs are properly executed. Care should be taken when applying sealant so as to prevent dirt from being attracted onto the metal surface. Sealants should be applied to dry, non-greasy surfaces.

-Special emphasis should be placed on the inspection of works that will be covered up by other components and elements. It should also be done to ensure that the contractor follows the shop drawing fixing details.

Steps to Install a Backer Rod:

Installing a backer rod is a relatively simple but crucial part of creating a durable seal in expansion joints, cracks, and other gaps before applying sealant. Here’s a step-by-step guide to installing a backer rod correctly, along with some helpful tips:

1. Choose the Correct Size:
   • Select a backer rod with a diameter slightly larger than the joint opening. The backer rod should fit snugly without being overly compressed, as this can affect the sealant’s adhesion and performance.
2. Prepare the Joint:
   • Clean the joint to remove debris, dirt, oil, or old sealant. This ensures a proper bond for both the backer rod and the sealant.
   • If needed, use a wire brush or other cleaning tools to prepare the surfaces.
3. Insert the Backer Rod:
   • Begin at one end of the joint and press the backer rod into the gap. You can use a blunt tool, like a putty knife or a special backer rod insertion tool, to push the rod into the joint to the desired depth.
   • Press the rod into the joint firmly but avoid over-compressing it. The goal is to leave some space between the backer rod and the sealant, which allows for flexibility and movement of the joint.
4. Ensure Uniform Depth:
   • The backer rod should sit approximately 1/8 to 1/4 inch below the joint surface, depending on the specific sealant and the manufacturer’s recommendations.
   • Use a tool to ensure the depth is uniform across the joint.
5. Handle Intersecting Joints:
   • If the joints intersect, do not cut the backer rod at the intersection. Instead, install the transverse rod above the longitudinal one, ensuring the depth and spacing requirements are maintained.
6. Check for Gaps:
   • Inspect the entire joint to ensure that the backer rod is continuous and there are no gaps or voids. Gaps can cause the sealant to perform poorly, leading to potential leaks or failure.
7. Install Sealant:
   • Once the backer rod is in place, you can apply the sealant according to the manufacturer’s guidelines.

Tips for Successful Installation:

• Avoid Compression: Do not compress the backer rod too much, especially for closed-cell foam rods, as excessive compression can distort the material and negatively affect the sealant’s performance.
• Don’t Twist or Stretch: Backer rods should not be twisted or stretched during installation, as this could damage the material or cause it to fit improperly.
• Minimize Cuts: Try to reduce the number of cuts to maintain the integrity of the backer rod. If cuts are necessary, ensure the cuts are clean and smooth.
• No Floating Rods: Ensure the backer rod fits snugly in the joint to avoid it “floating” when you apply the sealant.
• Use Proper Tools: Consider using a backer rod insertion tool for easier installation and to achieve the desired depth consistently.
• Temporary Joint Seals: If you use a backer rod temporarily (before applying the permanent sealant), make sure to replace it before final sealing to avoid compromising the joint.

To mitigate or prevent outgassing, consider the following best practices:

1. Avoid Puncturing the Backer Rod:
   • During installation, handle the foam backer rod carefully. Avoid puncturing or damaging the foam, as even a small rupture can lead to air escaping and outgassing.
   • Use tools specifically designed for backer rod installation, such as insertion tools or blunt-edged tools, to press the rod into the joint without causing damage.
2. Use the Correct Backer Rod:
   • If outgassing is a significant concern, consider using bi-cellular foam backer rods. These rods tend to be more resistant to puncturing and are less likely to outgas compared to extruded closed-cell foam.
   • If you must use closed-cell foam backer rods, choose ones that are non-porous and have a higher resistance to damage.
3. Inspect for Damage:
   • Before installing the backer rod, inspect it for punctures or other visible damage that could allow air to escape.
   • Avoid using backer rods that show signs of rupture or defects in the foam structure.
4. Ensure Proper Compression:
   • When pressing the backer rod into place, do so with uniform pressure. Avoid excessive compression, as this can cause the foam to rupture and release air.
5. Allow for Adequate Curing Time:
   • After applying the sealant, ensure that the sealant has sufficient curing time before subjecting the joint to environmental stresses, such as pressure or vibration. This allows the sealant to properly bond and set without interference from outgassing.

See also: https://codeconcrete.com/the-ultimate-guide-to-backer-rods/

Use the width of the narrowest and widest joints to set the range of joint widths to be filled. Estimate the likely range of service temperature and likely movement. Movement capacity will still vary depending on the specific brand of sealant selected, and therefore needs to be checked. The depth of sealant in the joint must be at least 6mm.

From manufacturer’s data, it will be good practice to find a specific sealant of the appropriate generic type, and make sure that it will not be subject to slumping when used to fill the widest joints.

Non-silicon base sealant should be used for external joints such as polysulphic sealant.

A sealed stone can resist the attack of the plasticiser by preventing the plasticiser from migrating into the pores of the stone.

Sealers for stones should be applied to prevent water from being retained in the pores of the stones. Sealers should have the following properties:

1. virtually odourless
2. non yellowing
3. deep penetrating protection
4. weather resistant
5. maximum stain resistance.

A good understanding of a joint sealant system is required especially for facade exposed to harsh outdoor environmental conditions subjected to cyclical temperature and moisture changes, thermal shock etc.

For this case, the reasons for the joint failure include:

• Poor workmanship in applying the sealant to joints due to lack of skillful labour
• Poor material selection for the sealant
• Water can dissolve the chemicals which thus make the sealant softened and lose its elasticity.
• Solvent evaporation
• Ozone attack, migration of plasticisers
• ultra-violet radiation
• Joint design: incorrect type of joint required with respect to dimensions, locations, joint spacing related to expected movement, shape and nature of backing material.

Also to note:

1. Sealants used shall be of suitable type to form a seal against water and air penetration and to withstand stresses during assembly, transportation, installation and operation of the curtain wall system. Sealants displaying predominantly elastic characteristics are recommended such as polysulphides, polyurethanes, silicones or other materials approved by the Specifying Authority.
2. Some cladding systems employ open joints concept allowing wind-driven rain and panel surface flow to enter the horizontal and vertical joints, which acts as a drainage system and discharge water away (Figure 1). Sealant is not required and thus sealant defects can be avoided. Other cladding systems have joints protected by gaskets instead. Open joint systems that use sealant that is recessed into the joint can protect the sealant from direct exposure to environmental elements such as ultraviolet rays (Figure 2). This may help to increase the durability of the sealant as compared to joints where the sealant is flushed with the panel surface allowing it to be directly exposed to ultraviolet radiation.
3. Use capping to protect the sealant joint. This will ensure that no chemical reaction will take place at the sealant joint.
4. Workmanship on-site should be ensured so that good designs are properly executed. Care should be taken when applying sealant so as to prevent dirt from being attracted onto the metal surface. Sealants should be applied to dry, non-greasy surfaces.
5. A maintenance schedule could be worked out so that the façade is cleaned periodically with cleaning agents recommended by the façade manufacturer.
6. Sealants must be continuous and of consistent quality.
7. Avoid bridging angles, particularly with mastic strip sealants. Apply extra thickness at corners as a precaution.

Design

Select sealant joint type and mode of application in accordance with BS 6213 or SS 654; including requirements for quality management programme. Adopt the guidelines on the selection of construction sealants in accordance with BS 8221-2, SS 509 or equivalent. For grading of sealant (i.e., pourable or non-sag), refer to ASTM C920-18 (tested), ASTM C639-15 or equivalent. Make provisions for access for regular sealant inspection and avoid placing design features/services across joints that impede access for maintenance.

Construction

Apply sealants in accordance with recommended guidelines in BS 8000-0, BS 6093, SS 654 or equivalent. Perform dynamic peel test and dynamic tensile test on structural sealants in accordance with ISO 28278-2 or equivalent. Carry out non-destructive and destructive inspection procedures of weatherproofing sealant joints in accordance with ASTM C1521-19, BS EN 15651-1 or equivalent. Use a two-cloth method to properly clean and prime.