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Sikaflex PRO: A Technical Overview
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Sikaflex® PRO is a professional-grade, moisture-curing, 1-component polyurethane sealant specifically formulated for Australian conditions. It provides a robust, flexible, and durable seal for movement and connection joints in concrete and masonry facades. Its formulation is engineered to provide a balanced profile of properties, including a high movement capability of ±25% (ASTM C 920), good workability for efficient application, and reliable adhesion to a wide range of common construction materials. This makes it an ideal solution for general sealing applications, both indoors and outdoors, where performance and longevity are paramount. The sealant cures to form a permanently elastic seal that resists weathering and aging, ensuring long-term structural integrity and reducing the likelihood of call-backs.
±25%
Movement Capability (ASTM C 719) to accommodate significant joint expansion and contraction without failure.
Core Features & Specifications
- High Elasticity & Movement Capability: Engineered with a movement capability of ±25% to handle dynamic joint movement, preventing bond failure during thermal cycles or structural shifts.
- Excellent Adhesion Profile: Bonds effectively to a wide range of porous and non-porous substrates, including concrete, masonry, and metals, often without the need for primers.
- Superior Workability: A smooth, paste-like consistency ensures easy gunning and tooling, allowing for neat, professional finishes with minimal effort.
- Durable & Weatherproof: Cures to a tough, resilient seal that withstands UV radiation, extreme temperatures (-40°C to +70°C), and harsh weather conditions for long-term performance.
- AS/NZS 4020 Potable Water Approval: Certified safe for contact with drinking water, making it suitable for sealing joints in potable water tanks and reservoirs.
- Paintable Surface: Can be over-painted with most conventional facade coating systems once fully cured, allowing for seamless integration with architectural finishes.
The Sikaflex PRO Advantage
- Reduce Costly Call-Backs: The exceptional elastic recovery of approximately 90% and robust adhesion ensure the joint remains sealed, minimizing rework and enhancing your reputation for quality.
- Increase On-Site Efficiency: With a skinning time of ~170 minutes and excellent workability, you have ample time to achieve a perfect finish, reducing waste and application stress.
- Versatile Project Application: From façade movement joints to perimeter sealing of windows and doors, a single, reliable product covers a vast range of common site tasks, simplifying inventory.
- Comply with Confidence: Meets critical industry standards, including ISO 11600 (Class F 25 LM) and ASTM C 920 (Class 25), ensuring your work meets engineering and architectural specifications.
- Achieve a Professional Finish: The sealant's consistent sag resistance (0 mm) and smooth tooling characteristics result in clean, sharp joint lines that enhance the building's aesthetic.
Best Practices: Do's & Don'ts
Do
- Ensure substrates are clean, dry, sound, and free from contaminants like oil, grease, and dust.
- Use a closed-cell polyethylene foam backing rod to control sealant depth and ensure a 2:1 width-to-depth ratio.
- Tool the sealant firmly against the joint sides to ensure full contact and proper adhesion.
- Conduct preliminary tests before over-painting to ensure paint compatibility.
Don't
- Use on natural stone, as it may cause staining.
- Apply to bituminous substrates, EPDM rubber, or materials that may bleed oils or plasticisers.
- Use for sealing joints in or around swimming pools or for permanent water immersion.
- Expose the uncured sealant to alcohol-containing products, as it can interfere with the curing reaction.
Applications in Practice: Trade Scenarios
For Commercial Builders: Sealing Concrete Precast Panel Joints
The Engineering Challenge
Sealing movement joints between large precast panels requires a sealant that can withstand significant thermal expansion and contraction while maintaining weatherproofing and complying with ASTM C 920 standards.
The System-Based Solution with Sikaflex PRO
For a 30 mm wide joint, install a suitable backing rod to a depth of 15 mm. Prime the clean, dry concrete surfaces with Sika® Primer-3 N. Extrude Sikaflex® PRO into the joint, ensuring a void-free application. Its ±25% movement capability and 0 mm sag flow make it ideal for these large vertical joints.
Best Practice Note
Allow the primer a flash-off time of at least 30 minutes (but less than 8 hours) before applying the sealant. Tool the surface within 150 minutes for a clean, professional finish.
For Carpenters & Installers: Perimeter Sealing of Window & Door Frames
The Engineering Challenge
Creating a durable, weatherproof seal around window and door perimeters is critical to prevent water ingress and air leaks. The sealant must adhere to multiple substrates like timber, aluminium, and brickwork.
The System-Based Solution with Sikaflex PRO
For a 10 mm joint, apply masking tape for sharp edges. For anodised aluminium frames, pre-treat with Sika® Aktivator-205. For porous brickwork, use Sika® Primer-3 N. Apply Sikaflex® PRO and tool firmly. The sealant's excellent adhesion and weather resistance ensure a long-lasting seal.
Best Practice Note
Remove masking tape within the skin time (~170 minutes) to avoid disturbing the sealant film and to achieve the neatest lines.
Performance Benchmark: Sikaflex PRO vs. Standard Alternatives
| Metric | Sikaflex PRO | Standard PU Sealant | Advantage |
|---|---|---|---|
| Movement Capability (ASTM C719) | ± 25% High Performance | ± 15% - ± 20% | Superior flexibility accommodates wider joint movement, reducing stress and failure risk. |
| Elastic Recovery (ISO 7389) | Approx. 90% Excellent | ~70-80% | Returns closer to its original shape after stretching, maintaining a tighter seal over time. |
| Potable Water Approval | Yes (AS/NZS 4020:2018) Certified | Not typically | Certified safe for use in drinking water applications, adding project versatility. |
| Tooling Time | Approx. 150 mins Extended | ~60-90 mins | Provides a longer window for achieving a high-quality finish, especially on large or complex jobs. |
Frequently Asked Questions
Can I paint over Sikaflex PRO sealant?
Yes, Sikaflex® PRO can be over-painted with most conventional facade paint systems. For best results, allow the sealant to cure fully before painting. It is critical to conduct preliminary trials to ensure paint compatibility, as non-flexible paint systems may crack or lose adhesion when applied over an elastic sealant. This ensures a durable and aesthetically pleasing finish for your project.
How long does Sikaflex PRO take to fully cure?
Sikaflex® PRO cures at a rate of approximately 3 mm per 24 hours at 23°C and 50% relative humidity. The full cure time will depend on the joint depth, temperature, and ambient humidity. For a 10 mm deep joint, you can expect it to take around 3-4 days to achieve a full cure. Curing will be slower in colder, drier conditions.
What is the correct joint size for using Sikaflex PRO?
The joint width for Sikaflex® PRO must be between 10 mm and 40 mm. Crucially, a width-to-depth ratio of 2:1 must be maintained for most applications (e.g., a 20 mm wide joint requires a 10 mm sealant depth). This design ensures the sealant can accommodate movement correctly. For joints up to 10 mm wide, a 1:1 ratio is acceptable.
Is Sikaflex PRO suitable for use on natural stone or in swimming pools?
No, you should not use Sikaflex® PRO on natural stone as it can cause staining. It is also not recommended for sealing joints in or around swimming pools or for applications involving permanent water immersion. For these specific applications, a specialised sealant like Sikasil® Pool or a SikaHyflex® product should be used.
Do I need a primer when using Sikaflex PRO?
While Sikaflex® PRO adheres to many substrates without a primer, for optimum adhesion and in critical applications (e.g., high-movement joints, extreme weather exposure), priming is required. For porous substrates like concrete use Sika® Primer-3 N. For non-porous substrates like aluminium or PVC, use the appropriate Sika® Aktivator or Primer as specified in the adhesion profile.
Applications & Benefits
| Application / Use Case | Key Benefit | Primary Trades |
|---|---|---|
| Movement joints in concrete/masonry facades | High movement capability (±25%) prevents cohesive failure from thermal cycling. | Builders, Remedial Contractors, Facade Installers |
| Connection joints (e.g., window/door perimeters) | Excellent adhesion to multiple substrates ensures a durable, weatherproof seal. | Carpenters, Glaziers, Builders |
| General indoor & outdoor sealing | Versatile, paintable, and easy to work with for a professional finish on various jobs. | All Trades |
| Sealing joints in potable water structures | AS/NZS 4020:2018 approval certifies it as safe for contact with drinking water. | Waterproofers, Civil Contractors |
| Sealing floor joints in low-traffic areas | Good tear resistance and moderate hardness provide durability against foot traffic. | Flooring Contractors, Builders |
Applying Sikaflex PRO: Enhanced Protocols & Best Practices
-
Step 1: Joint & Substrate Preparation
The foundation of a durable seal is a properly prepared substrate. Ensure the surface is structurally sound, clean, and dry.
Cleaning Porous Substrates (Concrete, Masonry)
Use a wire brush, grinding, or sandblasting to remove all laitance, dust, and loose material. Remove all contaminants like form-release agents, curing compounds, and old sealant residues.
Cleaning Non-Porous Substrates (Metals, PVC)
Clean with a suitable solvent and a clean, lint-free cloth. For metals, light abrasion may be required to remove oxidation. Always perform a final wipe to remove any residues.
Pro Tip: Use masking tape to protect the joint faces and ensure clean, sharp sealant lines. Apply the tape before priming. -
Step 2: Priming & Backing Rod Installation
For critical applications, priming is essential for optimal adhesion. Backing rods are non-negotiable for controlling sealant depth and preventing three-sided adhesion.
Primer Application
Apply the recommended Sika primer or activator in a thin, continuous film using a brush or clean cloth. Avoid ponding or over-application.
Backing Rod Installation
Insert a closed-cell polyethylene foam backing rod to the required depth to achieve the correct width-to-depth ratio (typically 2:1). Ensure the rod is compressed by approx. 25% to hold it in place.
Timing: Allow primers to fully flash off before applying sealant. This is typically 30-60 minutes, but check the primer's specific data sheet. Do not exceed the maximum overcoat time (usually 8 hours). -
Step 3: Sealant Application & Tooling
Proper application and tooling are crucial for a professional finish and long-term performance.
Application
Cut the nozzle to the required bead size. Extrude the sealant into the joint from the base, ensuring continuous, uniform application and avoiding any air entrapment.
Tooling Off
Firmly tool the sealant against the joint sides and backing rod. Use a spatula or slicker with a suitable tooling agent (e.g., Sika® Tooling Agent N) to create a smooth, concave finish that sheds water.
Timing: Tooling must be completed within the sealant's tooling time (~150 minutes). Remove masking tape immediately after tooling for the cleanest edges.
Limitations & Safety
Product Limitations
Not for use on natural stone surfaces such as marble or granite, as it may cause staining or discolouration.
Do not use in joints for swimming pools or any application with permanent water immersion or water pressure.
Use a specialised product like Sikasil® Pool.
Avoid contact with bituminous asphalt, natural rubber, or EPDM rubber as they may bleed oils that can degrade the sealant.
Colour variations may occur due to chemical exposure, high temperatures or UV-radiation (especially with white). This is aesthetic and does not affect performance.
Do not expose uncured sealant to alcohol-based products as this can inhibit the curing reaction.
Safety & Handling Requirements
Personal Protective Equipment
Wear chemical-resistant, impervious gloves (e.g., Butyl/Nitrile rubber), safety glasses/goggles compliant with AS/NZS 1337.1, and long-sleeved protective clothing.
Ventilation Requirements
Use only in well-ventilated areas. If vapours are generated, ensure local exhaust ventilation or wear appropriate respiratory protection.
Fire & Handling Precautions
Product is a combustible liquid (Category 4). Keep away from heat, sparks, open flames, and other ignition sources. No smoking.
Emergency First Aid
Eyes:
Flush immediately with plenty of water, also under the eyelids, for at least 15 minutes. Remove contact lenses. Seek medical advice.
Skin:
Take off contaminated clothing. Wash off with soap and plenty of water. If symptoms persist, call a physician.
Inhaled:
Move to fresh air. Consult a physician after significant exposure.
Swallowed:
Clean mouth with water and drink plenty of water afterwards. DO NOT induce vomiting. Never give anything by mouth to an unconscious person.
Seek medical attention immediately in all cases of serious exposure.
Sikaflex PRO Adhesion & Substrate Guide
Concrete / Masonry / Mortars
Surface Preparation
Substrate must be clean, dry, sound, and free from laitance, dust, and loose particles. Allow new concrete to cure for at least 28 days. Use mechanical means to remove any surface contaminants.
Primer Requirements
Primer Required for Optimal Adhesion
Apply one coat of primer with a clean brush to the prepared surface. Allow a flash-off time of >30 minutes (<8 hours) before applying sealant.
Sika® Primer-3 NAluminium / Steel / Powder Coated Metals
Surface Preparation
Clean surfaces thoroughly, removing all grease, oil, and contaminants. Lightly abrade the surface to remove any oxidation and wipe clean with a solvent-based cleaner.
Primer Requirements
Pre-treatment Required
Wipe on the activator with a clean, lint-free cloth. Allow a flash-off time of >15 minutes (<6 hours) before sealant application to ensure the surface is ready for bonding.
Sika® Aktivator-205PVC
Surface Preparation
Clean the PVC surface thoroughly to remove any surface gloss, dirt, or residues. Ensure the surface is completely dry before priming.
Primer Requirements
Primer Required
Apply primer with a clean brush in a thin, even coat. Allow a flash-off time of >30 minutes (<8 hours) before applying Sikaflex PRO.
Sika® Primer-215Timber
Surface Preparation
Timber must be sound, clean, and dry. Sand the surface and remove all dust. Ensure any existing coatings are fully cured and well-bonded. Moisture content must be appropriate for the timber type.
Primer Requirements
No Primer Typically Required
Sikaflex PRO generally adheres well to prepared timber. For critical applications or oily timbers, priming with Sika® Primer-3 N may be beneficial. Conduct a field test to confirm adhesion.
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