Key factors to consider when choosing concrete sealant
Concrete sealant selection and choosing the right joint sealants can be simplified as outlined below. Consider the following factors:
- Gap between the joints in millimeters
- Joint flexibility based on whether it undergoes expansion and contraction
- Exposure to the external environment
Sunlight – ensure the concrete sealant is UV resistant - Chemical resistance against corrosive chemicals, acids, and fuels
- Temperature range the assembly must withstand
- Expected service life of the joint, as sealants are sometimes used for temporary bonding
- Paintability – whether the concrete sealant can be painted over
- Cost or price of the product and its application
- Ease of application
Types Of Concrete Joint Sealant
Silicone Sealants for Concrete
Silicone sealants are high-performance elastomeric materials that create strong, durable, waterproof seals in construction joints. They are specially formulated to bond well with porous concrete and masonry while handling structural movement.
Key Types
- Neutral Cure Silicones: The best choice for concrete and masonry. They release non-acidic by-products (usually alcohol) that won’t damage the alkaline surface of concrete.
- Expansion Joint Silicones: High-movement sealants designed for large gaps in driveways and slabs.
- Self-Leveling Silicones: Ideal for horizontal surfaces like patios and garage floors. They flow easily to create a smooth, flat finish.
- Weatherproofing Silicones: UV-resistant formulas for exterior walls and building facades.
Common Uses
- Expansion & Control Joints: Filling gaps between concrete slabs to stop water from reaching the base.
- Driveway & Patio Repairs: Sealing cracks to prevent widening from freeze-thaw cycles.
- Wall-to-Floor Transitions: Creating tight seals where concrete meets walls or other materials.
- Building Facades: Protecting joints in precast panels from rain and wind.
Core Advantages
- Long-Term Flexibility: Stays elastic in extreme temperatures (-50°C to 150°C) without becoming brittle.
- Superior UV Resistance: Resists sunlight damage and won’t chalk or degrade outdoors.
- Fast Weather Resistance: Some products become rain-ready in just 3 hours.
- High Movement Capability: Can handle ±25% to ±50% joint movement without losing adhesion.
Polyurethane Sealants/ PU Sealants
Characteristics of PU Sealants
PU sealants deliver high gap filling and strong bonding. Moreover, they remain flexible under stress. They also resist chemicals and harsh weather. In addition, users can paint over them for a clean finish.
Key Construction Applications
- Expansion & Control Joints: Ideal for concrete floors, roads, bridges, and airport runways. They absorb repeated movement while keeping strong adhesion.
- Waterproofing: Perfect for sealing roofs, basements, foundations, and tunnels to block water.
- Precast Concrete: Seals joints and connections between precast concrete elements.
- Structural Bonding: Fixes door and window frames to masonry, wood, or metal with airtight, watertight seals.
- Crack Repair: Fills and repairs cracks in walls, sidewalks, and high-traffic driveways.
- Infrastructure: Protects dams, culverts, and hydraulic structures from long-term damage.
Industry Benefits
- Flexibility: Construction-grade PU sealants handle ±25% to ±35% joint movement without cracking.
- Paintability: Unlike silicone, they can be painted after curing to match the building’s look.
- Adhesion: Strong, often primerless bonding to concrete, wood, metal, and plastic.
- Toughness: More resistant to abrasion and tearing than silicones, making them excellent for busy floor joints.
Concrete Acrylic Sealants
Concrete acrylic sealants are versatile, water-based products used for sealing joints and cracks in masonry. They work best for indoor, low-movement areas where a neat, attractive finish is needed.
Common Uses
- Joint & Crack Sealing: Fills gaps in concrete walls, floors, and panels to block dust and water.
- Interior Finishing: Seals around doors, windows, and skirting boards for a clean, paint-ready finish.
- Decorative Concrete: Acts as a protective film-forming sealer that enhances colour on stamped or stained surfaces.
- Precast & Masonry: Ideal for joints in brick, plasterboard, and other porous materials.
Core Advantages
- Paintability: Easily painted after curing, blending perfectly with surrounding surfaces.
- Ease of Use: Simple to apply with a caulking gun and cleans up with water while wet.
- Cost-Effective: More affordable than silicone or polyurethane, great for large indoor jobs.
- Eco-Friendly: Many are low-VOC, making them safer for indoor air quality.
- UV Resistance: Quality acrylics resist yellowing and fading over time
Hybrid MS Polymer sealant
What Is an MS Polymer Adhesive and Sealant?
MS polymer sealants deliver high strength and elasticity. They bond well to non-porous and even damp surfaces. Moreover, they accept most paints. As hybrid sealants, they combine polyurethane strength with silicone weather resistance. In addition, they are solvent-free and isocyanate-free. This makes them safer and easy to customize for viscosity and fast strength build-up.
They offer high initial tack and instant bonding. However, they have low gap-filling ability. Therefore, users choose them mainly for bonding rather than sealing. Common uses include mirror, panel, and cladding bonding.
Benefits of MS Polymer Sealants
First, high initial tack reduces the need for support. Next, they apply and finish easily. They also stay elastic after curing. Moreover, they have no odor and contain no solvents, silicones, or isocyanates. Additionally, they accept water-based paints. Finally, they provide excellent color stability plus strong weather and UV resistance. They even bond on wet surfaces and underwater.
Joint Sealant Terminology – Concrete Sealers
ASTM C920 is the global standard for elastomeric joint sealants. It combines key test methods, including:
Movement capability: ASTM C719
Sealant hardness: ASTM C661
Tack-free time: ASTM C679
Peel adhesion: ASTM C794
Together, these tests define sealant performance.
Movement Capability – ASTM C719
This test measures how much cyclic movement a sealant handles under simulated weathering. Based on results, sealants fall into movement classes:
±12.5% → Class 12.5
±25% → Class 25
±35% → Class 35
±50% → Class 50
+100% / -50% → Class 100/50
Higher class ratings mean greater joint movement capacity.
Sealant Hardness – ASTM C661
This test checks resistance to penetration using a durometer probe. Ratings range from 0 to 100.
Lower values mean softer sealants with higher movement capacity.
Higher values mean harder sealants with lower movement capacity.
Stress Relaxation
This test checks how well a sealant absorbs extension without adding stress to the bond line. Quick and full recovery results in lower stress relaxation values.
Modulus
Low-modulus sealants create low stress at the bond line. Therefore, they suit high-movement joints.
Medium-modulus sealants handle most general applications.
High-modulus sealants suit glazing and static joints, not moving joints.
What Is a Sealant Used For?
Joint sealants block fluids, air, dust, sound, and insects from passing through joints and openings. Moreover, they can act as firestopping barriers in construction.
Adhesive vs. Sealant: Key Difference
Sealants fill and close gaps to create air- and water-tight joints. Adhesives, however, bond materials together. In short, adhesives bond first and seal second.
How to Prevent Sealant Failure
Sealants cause many building issues despite their low cost share. However, failures occur when bonding to the substrate breaks or the sealant tears.
Usually, two mistakes lead to failure. First, poor surface preparation. Second, choosing the wrong product. Therefore, always prepare substrates properly and select the right sealant for the application.