Understanding Different Types of Sealants

Choosing the wrong sealant is one of the most common DIY mistakes. That tube of general-purpose silicone might seem like it'll work everywhere, but use it in the wrong application and you'll be redoing the job within months. Understanding what sets each sealant type apart helps you make the right choice the first time.

Each sealant type has been engineered for specific conditions and materials. The chemistry behind these products determines their flexibility, adhesion, durability, and resistance to various environmental factors. Let's break down the major categories.

Silicone Sealants

Silicone is the most widely used sealant type for good reason—it's extremely versatile and durable. Made from synthetic polymers, silicone maintains its flexibility over a wide temperature range and resists water, UV rays, and many chemicals.

Types of Silicone

Not all silicone sealants are the same. The curing mechanism creates important distinctions:

Best Uses for Silicone

• Bathroom sealing around baths, showers, and basins
• Kitchen benchtops and sink surrounds
• Glass installation and aquariums
• Exterior glazing and weathersealing
• High-temperature applications (exhaust systems, ovens)

Limitations

Silicone's major drawback is that it cannot be painted. The surface resists paint adhesion, making it unsuitable where a painted finish is required. It also doesn't adhere well to some plastics and certain porous surfaces without primer.

Acrylic Sealants

Acrylic sealants (also called acrylic latex or painter's caulk) are water-based products popular for interior applications. They're easy to work with, clean up with water, and can be painted once cured.

Characteristics

Acrylics are typically less expensive than silicone and offer good adhesion to a wide range of porous surfaces including timber, plaster, and masonry. They fill gaps well and can be sanded smooth after curing.

However, acrylics are not truly waterproof. They're water-resistant when cured, but prolonged water exposure—like in a shower—will cause them to break down. They're also less flexible than silicone and can crack if the joint experiences significant movement.

Best Uses for Acrylic

• Interior trim and architrave gaps
• Filling cracks in plaster and drywall
• Skirting board joints
• Window and door frame gaps (interior side)
• Any application requiring a painted finish in dry areas

Polyurethane Sealants

Polyurethane sealants are the workhorses of the construction industry. They offer superior adhesion, excellent durability, and can handle significant joint movement—making them ideal for demanding applications.

Characteristics

Polyurethanes bond strongly to almost any building material: concrete, timber, metal, most plastics, and masonry. They remain flexible over time and resist weathering, making them suitable for exterior applications. Many polyurethanes can also be painted.

The main drawbacks are higher cost, more difficult cleanup (requiring solvents), and limited UV resistance in some formulations. Unpainted polyurethane exposed to direct sunlight may degrade faster than silicone.

Best Uses for Polyurethane

• Expansion joints in concrete and masonry
• Exterior window and door perimeters
• Roofing and flashing applications
• Construction joints in commercial buildings
• Bonding dissimilar materials
• High-movement joints

Hybrid Sealants

Hybrid sealants combine technologies—typically silicone-modified polyurethane (SMP) or MS polymer formulations—to offer the best properties of multiple sealant types.

Characteristics

These modern formulations often provide the flexibility and water resistance of silicone with the paintability and adhesion of polyurethane. Many are also low-odour, solvent-free, and easier to tool than traditional options.

Hybrids have become increasingly popular for general-purpose applications because they reduce the need to stock multiple sealant types. However, they may not match the performance of specialised products in extreme conditions.

Specialty Sealants

Beyond the main categories, specialty sealants address specific requirements:

Fire-Rated Sealants

Required where penetrations pass through fire-rated walls or floors. These intumescent sealants expand when exposed to heat, maintaining the fire barrier. Always specify these for any penetration through fire-rated construction.

Butyl Sealants

Excellent for metal-to-metal applications, particularly roofing. Butyl provides outstanding adhesion to metals and maintains flexibility in extreme temperatures. Common in gutter installations and metal cladding.

Acoustic Sealants

Designed to maintain acoustic ratings in sound-rated walls. These remain permanently flexible to prevent sound transmission through joints. Essential in apartments, home theatres, and commercial spaces requiring noise control.

Food-Grade Sealants

For commercial kitchens and food processing areas. These sealants meet hygiene standards and resist the aggressive cleaning chemicals used in food preparation environments.

Making the Right Choice

When selecting a sealant, consider these factors:

• Water exposure: For wet areas, only true silicone or appropriate hybrids will do
• Movement: High-movement joints need polyurethane or hybrid products
• Painting: If you need to paint, eliminate standard silicone from consideration
• Materials being sealed: Acid-cure silicone damages some materials—check compatibility
• Indoor vs outdoor: Exterior applications need UV-stable products
• Temperature range: Check specifications if exposure to extreme temperatures is expected

Reading Product Labels

Product marketing can be misleading. Terms like "kitchen and bathroom" on acrylic products don't mean they're suitable for shower enclosures. Always read the technical data sheet—not just the front label—to understand a product's true capabilities and limitations.

Look for specific claims about water immersion resistance (not just "water resistant"), flexibility percentages, and recommended applications. If a wet-area product doesn't explicitly state it's suitable for shower recesses, assume it isn't.

Understanding sealant types empowers you to make informed decisions and achieve professional results. When in doubt, choose a product specifically designed for your application—the small additional cost is far less than redoing a failed seal.