How to Apply Joint Sealants Without Problems

How to Apply Joint Sealants Without Problems?

Applying joint sealants correctly is essential for a durable and effective seal. Here’s a step-by-step guide:

Preparation is Key:

  • Choose the right sealant: Consider the type of joint, the materials involved, and environmental conditions. Refer to “How To Choose A Sealant” article.
  • Prepare the joint: Ensure the joint is clean, dry, and free from contaminants. Remove any old sealant residue.
    • 1. Clean the Joint Thoroughly:
      • Remove all contaminants: This includes dirt, grease, oil, paint, old sealant, and loose particles.
      • Use appropriate cleaning agents: Choose a cleaner suitable for the surface material. Isopropyl alcohol or a mild detergent solution often works well.
    • Dry completely: Ensure the joint is completely dry before applying the sealant.
    • 2. Remove Old Sealant:
      • Scrape off old sealant: Use a putty knife or scraper to remove any existing sealant.
      • Prime the surface: If necessary, apply a primer recommended by the sealant manufacturer to enhance adhesion.

    • 3. Create a Suitable Joint Profile:
      • Backer rod: For larger joints, insert a backer rod to control sealant depth and improve adhesion.
      • Joint depth: The joint should be deep enough to accommodate the sealant but not too deep. Minimum depth is 6mm. Generally, width:depth ratio is
        • 2:1 if joint width>=12mm
        • 1:1 if joint width <12mm
      • Joint shape: Ensure the joint is clean and well-defined for optimal sealant application. Sealant bead in hour-glass shape is recommended for ease of movement.
      • Corner / Fillet Joint: ensure a minimum 6mm bonded substrate is available on both surfaces.

For more information about joint profile, please see this page: How to determine the width and depth of a sealant joint

    • 4. Prime the Surface (Optional):
      • Check sealant compatibility: Some sealants require a primer for specific substrates. To achieve optimal adhesion result on porous substrates like concrete, a primer is recommended.
      • Apply primer as directed: each product would have different characteristics, like different length of curing time.
  • Use backer rod: Use a backer rod to control sealant depth, improve adhesion (tool sealant with a base so it is pushed towards the joint flank for wetting), and most importantly – prevent three-sided bonding. Sealant is supposed to bond only to both joint flanks without adhering to the bottom, otherwise the movement capability would be greatly reduced. Factors to Consider:
    •  Joint Size: The diameter of the backer rod should be approximately 25% smaller than the joint width. For instance, for a 1/2 inch joint, a 3/8 inch backer rod would be suitable.
    • Joint Movement: For joints that experience significant movement, consider using a more flexible backer rod like open-cell foam.  
    • Sealant Type: The backer rod should be compatible with the sealant you’re using.
    • Environmental Conditions: If the joint is exposed to harsh weather conditions, a closed-cell backer rod might be more suitable due to its resistance to moisture and UV rays. 
    • Joint Location: For horizontal joints, a closed-cell backer rod is generally preferred to prevent water penetration. For vertical joints, open-cell backer rod can be used. 
    • Joint substrates: if substrates are non-porous, avoid using close-cell backer rod due to less amount of air and moisture allowed to pass through for moisture-curing sealants to cure.

    • Types of Backer Rods:
      • Open-cell foam: Flexible, easy to install, and allows moisture vapor to escape.
      • Closed-cell foam: More rigid, provides better water resistance, ideal for horizontal joints. Beware when inserting closed-cell backer rod because if punctured, it will outgas and cause bubble in sealant.

Bond Break Tape:

  • Use a bond breaker tape instead if the joint it too shallow to insert a backer rod
  • Bond breaker tape can be any tapes that are not easy to bond, such as PP or PTFE tapes.
    • Installation Tips:
    •  Clean the joint: Remove any debris or contaminants before inserting the backer rod.
    • Compression: The backer rod should compress slightly when inserted into the joint.
    • Even distribution: Ensure the backer rod is evenly distributed throughout the joint.
    • Use a backer rod roller if possible. Backer rods that are inserted into the joint in a uniform manner would determine a consistent depth of sealant bead and sealant adhesion improvement, which can affect the movement performance of the sealant and overall functionality.

Application Process:

  • Apply sealant evenly:
    • Cut the Nozzle at a 45-degree angle. This allows for a smooth and even flow of sealant. Adjust the size of the opening based on the desired bead size.
    • Hold the Caulking Gun at a 45-degree angle, pointing the nozzle towards the joint.   Apply steady, even pressure to the trigger. 
    • Applying the Sealant:  Start at one end of the joint and move slowly and continuously. Maintain a consistent speed to ensure an even bead and no air trap.
  • Tooling:
    • Use a sealant smoother or your finger (if dampened with water) to shape the sealant into a neat and even bead.
    • Smooth the sealant in one direction to avoid air bubbles.
    • Do not use soapy water or even solvent to tool sealant to get smooth finishing. It may discolor the sealant, and worse, if gets on the edge of the sealant, it can affect adhesion.            
    • Tips: For joints with uneven joint surfaces, use a rubber scrapper instead of metal /plastic scrapper to tool, so it can accommodate the unevenness of the joint
  • Curing time:
    • Allow the sealant to cure completely, generally it takes 3 – 7 days depending on factors like sealant thickness, temperature, humidity, types of substrates, etc.
    • Avoid exposure to moisture or extreme temperatures during curing.
    • Avoid joint movements caused by external force, such as vibrations due to workers walking on the substrates (roofing, slabs, etc.). This is  a common cause of adhesion failure – joint movements before full cure of sealant.

Additional Tips:

    • Weather conditions: Ideal application conditions are typically between 10°C and 35°C.
    • Testing: Perform a pull test after curing to ensure proper adhesion.

FAQ:

  1. How long does sealant take to cure?

    The curing time for sealant can vary depending on several factors:
  • Temperature: Warmer temperatures generally speed up curing times, while cooler temperatures slow it down.
  • Humidity: Higher humidity can accelerate the curing process for some sealants, while others may require lower humidity.
  • Thickness of Application: Thicker layers of sealant will take longer to cure.
  • Ventilation: Good ventilation can aid in the curing process by allowing moisture or solvent to evaporate more quickly.
  • Adjacent Substrates: If the joint flanks are non-porous, and the backer rod is of closed-cell material like Polyethylene, there is less air or moisture reaching the sealant for curing process
  • Product Properties: Every sealant has different skin forming and cure-through speed, even if they are from the same type/category or from the same brand.

Here are some general guidelines for different types of sealants:

Sealant Type

Skin Formation Time*

Full Curing Time*

Silicone Sealant

5 to 20 minutes

Vary greatly depends on factors mentioned above. Generally range from 1 to 7 days.

Acrylic Latex Sealant

10 to 20 minutes

MS Polymer Sealant

20 to 40 minutes

Polyurethane Sealant

1 to 2 hours

*Always refer to the specific product TDS for exact information.

2. What will happen if I apply sealant into joint without following the proper sealant bead size?

Applying sealant without following the proper bead size can lead to several potential issues, affecting the performance, durability, and appearance of the seal. Here’s what might happen if the sealant bead size is incorrect:

  1. Insufficient Coverage (Too Small Bead Size)
  • Inadequate Sealing: If the bead is too small, it may not provide enough material to fill the joint properly, leading to gaps and potential leaks. This can result in water infiltration, air leakage, or loss of energy efficiency.
  • Weak Adhesion (adhesion failure): A thin bead might not adhere well to the surfaces, reducing the sealant’s ability to hold and seal effectively. This can compromise the integrity of the joint, leading to premature failure. As a rule of thumb, always ensure a minimum 6mm bonded substrate.
  • Vulnerability to Movement: Joints may experience movement due to thermal expansion, contraction, or other factors. A small bead might not accommodate this movement, causing the seal to crack (cohesion failure).
  • Aesthetic Issues: Insufficient sealant can result in uneven, thin, or recessed joints, leading to an unsightly finish that detracts from the appearance of the surface.
  1. Excessive Sealant (Too Large Bead Size)
  • Waste of Material: Using more sealant than necessary is wasteful and increases project costs without adding value.
  • Longer Curing Time: Excessive sealant takes longer to cure, which can delay project completion and leave the joint vulnerable to disturbance or damage.
  • Aesthetic Problems: A large bead can overflow, creating a messy, unprofessional appearance. It can be difficult to achieve a clean line, and excess material might need to be trimmed or cleaned off surrounding surfaces.
  • Potential for Cracking: An overly thick bead may become brittle once cured and be more prone to cracking, especially in areas subject to movement or vibration.
  • Stress on Substrates: Excessive sealant can exert pressure on the bonding line and bonded substrates, potentially leading to issues with adhesion (adhesion failure) or damage to the surfaces (material failure) being sealed.
  1. Functional Issues
  • Incompatibility with Joint Design: Different joints are designed for specific sealant bead sizes to accommodate movement, bonding, and environmental exposure. Incorrect bead size can lead to functional failures.
  • Performance Degradation: The sealant’s intended performance properties, such as flexibility, tensile strength, and weather resistance, may be compromised if the bead size is not appropriate. When sealant bead is overly thick, it will not be able to move as claimed by the manufacturer (e.g. +-12.5%, +-25%, +-50%).