Injectable sealant is a high-performance, viscous material designed to fill gaps, cracks, and voids in various substrates, creating a durable, watertight, and airtight barrier. Unlike traditional sealants that are applied superficially, injectable sealants are forced deep into flaws using specialized injection equipment, ensuring the repair reaches the root of the problem. This makes them indispensable in construction, automotive, marine, and industrial maintenance for tasks ranging from concrete crack repair to gasket formation and leak sealing.
The effectiveness of an injectable sealant lies in its formulation. Modern products are often based on advanced polymers like polyurethane, epoxy, or silicone, which offer exceptional adhesion, flexibility, and resistance to environmental stressors. They cure—either by reacting with moisture in the air (moisture-cure) or through a chemical reaction between two components (multi-component)—to form a tough, resilient seal that can withstand movement, pressure, and harsh conditions.
Understanding the technical specifications is crucial for selecting the right injectable sealant for your project. The following parameters determine the product's performance, application suitability, and longevity.
| Parameter | Polyurethane-Based | Epoxy-Based | Silicone-Based | MS Polymer-Based |
|---|---|---|---|---|
| Typical Viscosity | 5,000 - 50,000 cP | 1,000 - 15,000 cP (low-viscosity grades) | 10,000 - 80,000 cP | 8,000 - 40,000 cP |
| Cure Type | Moisture-Cure or 2-Part | 2-Part | Moisture-Cure | Moisture-Cure |
| Full Cure Time | 24 - 72 hours | 4 - 24 hours | 24 - 48 hours | 24 - 48 hours |
| Shore Hardness | A 30 - A 70 | D 60 - D 85 | A 20 - A 50 | A 40 - A 70 |
| Elongation at Break | 400% - 1000% | 3% - 10% | 300% - 900% | 400% - 600% |
| Tensile Strength | 2 - 5 MPa | 20 - 50 MPa | 4 - 8 MPa | 4 - 10 MPa |
| Service Temperature | -40°C to 80°C | -30°C to 120°C | -60°C to 200°C | -40°C to 100°C |
| Chemical Resistance (Water/Fuels) | Excellent / Good | Excellent / Excellent | Excellent / Fair | Excellent / Good |
| Primary Applications | Construction joints, concrete cracks, automotive seams | Structural repairs, bonding, anchoring, industrial flooring | High-temp gaskets, glass, marine fittings | Transportation, Prefab construction, general industry |
What is the main advantage of using an injectable sealant over a surface-applied sealant?
The primary advantage is the depth and completeness of the seal. Surface-applied sealants only address the visible part of a crack, leaving the underlying void vulnerable. Injectable sealants are pumped under pressure to fill the entire void from the inside out, creating a three-dimensional seal that blocks moisture, air, and contaminants throughout the entire flaw. This results in a more durable, long-lasting, and structurally sound repair, especially for subsurface leaks or cracks in foundations, walls, and pipes.
How do I choose between a polyurethane and an epoxy injectable sealant?
The choice depends entirely on the nature of your repair. Use polyurethane sealants for dynamic cracks and joints that experience movement, thermal expansion, or vibration. Their high flexibility and elongation allow them to move with the substrate without cracking. Choose epoxy sealants for static cracks where you need to restore structural strength and rigidity, such as in concrete beams or bonding metal to concrete. Epoxy bonds tenaciously and has high compressive strength but is brittle and will crack if the joint moves.
Can injectable sealants be used to stop active water leaks?
Yes, certain types are specifically designed for this purpose. Hydroactive polyurethane injectable sealants are the best choice. Upon contact with water, they rapidly expand into a firm, flexible foam that blocks the water flow. They can even be injected against active water pressure, making them ideal for emergency leak-stopping in foundations, basements, tunnels, and swimming pools. It is crucial to select a product labeled for "water-active" or "hydrophobic" injection for such applications.
What equipment is needed to apply an injectable sealant?
The equipment varies with the sealant type and scale of the job. For small-scale or DIY projects with cartridge-based sealants, a standard caulking gun may suffice. For professional applications, specialized injection equipment is required. For moisture-cure polyurethanes and silicones, a single-component air-powered or electric injection pump is used. For two-component epoxies and polyurethanes, a dual-cartridge dispenser with a static mixer nozzle or a plural-component pump with a dynamic mixer is necessary to properly meter and mix the components at the point of application.
How should I prepare the surface before injection?
Proper surface preparation is critical for adhesion. First, clean the area around the injection point thoroughly to remove all loose debris, dust, oil, and old sealant. For the best results, use a wire brush, compressed air, or a vacuum. If the crack is superficial, it may be necessary to widen it slightly using a grinder or chisel to create a "V" groove, which aids in injection and provides a key for the sealant. For precise injection, surface ports may need to be installed and sealed around the crack to direct the flow of the sealant.
What is the typical coverage or yield of an injectable sealant cartridge?
Coverage is highly dependent on the width and depth of the crack or void being filled. As a rough estimate, a standard 300ml cartridge can fill approximately 1 to 3 linear meters of a crack that is 5mm wide and 10mm deep. For larger volume voids, yield is calculated based on the total volume to be filled (length x width x depth). Always consult the manufacturer's technical data sheet for the specific yield information of the product you are using, as viscosity and cure expansion characteristics greatly affect the final volume.
Are there any safety precautions I should take when using injectable sealants?
Yes, always prioritize safety. Wear appropriate Personal Protective Equipment (PPE), including safety glasses, chemical-resistant gloves, and long-sleeved clothing. Work in a well-ventilated area to avoid inhaling fumes, especially from solvent-based or isocyanate-containing products (common in some polyurethanes). Read and follow all instructions and hazard warnings on the product's Safety Data Sheet (SDS). Avoid skin contact, and if contact occurs, wash thoroughly with soap and water. Keep the product away from open flames or sparks.
Can I paint over an injectable sealant after it has cured?
This depends on the sealant's chemistry. Most epoxy and some polyurethane sealants can be painted over once they have fully cured. However, standard silicone sealants cannot be painted, as paint will not adhere to their non-stick surface. Some advanced MS polymer and specialty polyurethane sealants are paintable. Always check the product's technical data sheet or container label for "paintable" or "over-paintable" designations and follow the recommended waiting period after curing before applying paint.
How long does an injectable sealant repair typically last?
When applied correctly to a properly prepared surface, a high-quality injectable sealant repair can last for the lifetime of the structure, often 20 years or more. The longevity is influenced by the sealant's resistance to UV radiation, temperature cycling, chemical exposure, and mechanical stress. For example, a silicone sealant on an exterior joint may last over 50 years due to its superior UV stability, while a polyurethane sealant in a submerged or high-movement application may have a service life of 20-30 years.
What is the difference between a flexible and a rigid injectable sealant?
The core difference lies in their Shore Hardness and Elongation properties. A flexible sealant, like most polyurethanes and silicones, has a low Shore A hardness (e.g., 20-50) and high elongation (over 300%). It remains pliable, allowing it to absorb movement and vibration without losing its seal. A rigid sealant, like epoxy, has a high Shore D hardness (e.g., 60+) and very low elongation (less than 10%). It creates a hard, unyielding plug that is excellent for structural bonding but will crack if the substrate moves. The application dictates which type is appropriate.
