Silicone vs. Polyurethane: A Comprehensive Guide to Adhesives and Sealants
When it comes to choosing between silicone and polyurethane products, the options seem endless. Whether you're installing a new Colorbond® roof or working on truck fabrication, adhesives and sealants are essential tools in countless applications. Understanding the differences between these materials and knowing where to use them is crucial. Silicone is widely recognized among builders for its versatility, from kitchen installations to roofing and plumbing. On the other hand, polyurethane, with its impressive flexibility after curing, is favored in steel fabrication sectors such as coach and bus manufacturing or emergency vehicle outfitting. Generally speaking, polyurethane excels in resisting stretching and handling vibrational movements better than silicone, which struggles with vibration resistance. For dynamic applications involving vibration or wear, polyurethane tends to be the superior choice.
In this post, we’ll delve deeper into these popular elastomer products and offer some practical guidance on their applications. Before we proceed, let’s address the fundamental question: how will you use these products? Are you looking for an adhesive or a sealant? While an adhesive is a high-strength product meant to join two materials together, a sealant serves as a lower-strength caulk that fills and seals gaps between different materials. This distinction is straightforward, but you’ll find that some adhesives work well as sealants and vice versa. Knowing your project requirements and desired outcomes is key to selecting the right product.
### Silicone or Polyurethane for Your Project?
In the construction industry, silicone is typically regarded as superior to polyurethane, though it does have certain limitations. One major drawback of silicone is that it cannot be painted—other caulking products are needed for painted applications. This article provides a general overview to help you determine which type of caulk suits your project best.
#### When to Use Polyurethane
Choose polyurethane when you need a surface that will be painted. Polyurethane adheres well to a wide range of surfaces with minimal limitations. Most manufacturers offer warranties lasting five years, but you might expect up to ten years if sunlight exposure and joint movement are minimal. Polyurethane is easier to clean than silicone and takes about 24 hours to dry. Once cured, it becomes challenging to remove.
#### When to Use Silicone
Silicone performs exceptionally well on wet or exterior surfaces that don’t require painting. It holds up well under sunlight and extreme temperatures.
### Silicone vs. Polyurethane Overview Table
| Feature | Seal Flex (Polyurethane) | Industrial Grade (Silicone) |
|-----------------------------|-------------------------------------|-------------------------------------|
| Weather Resistance | Good | Great |
| Tensile Strength | 1.6N | 1.7N |
| Service Temperature | -30°C to 90°C | -62°C to 177°C |
| Joint Movement | ±20% | ±25% |
| Abrasion Resistance | Excellent | Poor |
| Tool Time | 10-15 minutes | 3-5 minutes |
| Curing Time | 3mm/24hrs | 2mm/24hrs |
| Shore A Hardness | 40±5 | 27 |
| Elongation at Break | >600% | >500% |
### Advantages and Disadvantages
Both silicone and polyurethane possess unique properties and are suited to different applications. Selecting the right material depends on the specific needs of your project.
#### Polyurethane Pros:
- High strength and durability—can handle heavy loads/impacts.
- Resists abrasion, chemicals, and oil effectively.
- Maintains flexibility across a wide temperature range.
- Paintable and bonds well with various materials.
#### Polyurethane Cons:
- Poor temperature resistance; degrades at high temperatures.
- Releases volatile organic compounds (VOCs) during curing.
- Not suitable for medical applications due to toxicity concerns.
#### Silicone Pros:
- Exceptional temperature resistance—can endure extreme heat and cold.
- High flexibility maintains properties over a wide temperature range.
- Excellent electrical insulation prevents electricity flow.
- Resistant to moisture, chemicals, and UV light.
- Non-toxic, safe for medical use.
#### Silicone Cons:
- Low tear resistance.
- Difficult to paint.
- Can have a sticky or tacky surface.
### Chemical Differences Between Silicone and Polyurethane
Silicone is a synthetic polymer made primarily of silica, oxygen, carbon, and hydrogen atoms. Its main ingredient is silica—one of the most common forms of sand. Polyurethane results from a chemical reaction between a polyol resin and a poly-isocyanate, which acts as a curing agent. The resin portion can be modified with polyester, polyether, or acrylic. Polyurethane has a highly cross-linked synthetic chemical structure.
### Popular Polyurethane Brands
Here are some examples of the many polyurethane sealants available in Australia. The specific type and brand you choose will depend on your application and project requirements.
- **Aerobolt Seal Flex**: Aerobolt's top-selling general-purpose polyurethane adhesive and joint sealant, ideal for industrial and construction uses. Seal-Flex cures quickly to form a durable, flexible, and paintable seal that absorbs vibrations. If you need a structural adhesive with strong load-bearing capabilities, consider Bond Flex or Bond Flex Plus.
- **Bostik Seal N Flex**: Another popular polyurethane sealant in Australia, designed for construction and automotive applications. Known for its flexibility and ability to withstand extreme temperatures and weather conditions.
- **Tremco Vulkem**: Often used in roofing and waterproofing, Tremco Vulkem offers a durable, long-lasting seal that resists harsh weather and UV radiation.
- **3M Marine Adhesive Sealant**: Specifically designed for marine environments, this polyurethane sealant is waterproof, weather-resistant, and capable of withstanding saltwater and corrosive substances.
- **Soudal Fix All**: A multi-purpose polyurethane sealant suitable for a variety of applications. It boasts high bonding strength, fast curing, and the ability to seal gaps and cracks in multiple materials.
### Popular Silicone Brands
Australia offers a wide range of silicone sealants, each with distinct features and applications. Here are some examples:
- **Bostik Industrial Grade Silicone**: Offers excellent adhesive properties for various construction surfaces, including glass, aluminum, wood, brick, and masonry. Permanent flexibility after curing makes it a general-purpose adhesive and sealant.
- **Selleys All Clear**: Widely used in bathrooms, kitchens, and wet areas, Selleys All Clear is flexible, waterproof, and resistant to mildew and mold growth.
- **Bostik 5CLM**: A high-performance construction silicone ideal for high joint movement. It cures by absorbing atmospheric moisture to form a flexible and durable sealant suitable for natural stones and facade panels.
- **Dowsil 732**: Versatile and used in construction, electrical, and automotive industries. Known for its high strength, durability, and resistance to temperature extremes.
- **Bostik Roof and Gutter**: Designed specifically for roofing and guttering, this silicone adhesive sealant adheres well to metal, concrete, and tiles.
- **Geocel Trade Mate**: A multi-purpose silicone sealant used in construction, plumbing, and electrical work. Known for its high strength, flexibility, and resistance to weathering and UV radiation.
- **Bostik 6S**: A neutral-cure silicone that releases a faint alcoholic vapor during drying, making it suitable for indoor use. It adheres well to powder-coated steel and glass and won't sag in typical joints.
- **Tremco Proglaze**: Specifically designed for curtain wall and facade systems, Tremco Proglaze excels in adhesion to glass, metal, and other materials while resisting UV radiation and weathering.
These are just a few examples of the many silicone sealants available in Australia. The right type and brand depend on your specific application and project requirements.
### Summary of Silicone vs. Polyurethane
In summary, choosing between silicone and polyurethane depends on your specific situation. Silicone is ideal for applications requiring high-temperature and weather resistance without painting. Polyurethane is better suited for projects demanding high strength, durability, and resistance to abrasion and chemicals. At Aerobolt, we offer a comprehensive range of silicones, polyurethanes, and other adhesives like our MS Polymer range. For assistance with selection and application, feel free to call us at 02 9755 3747 or reach out to us directly.
### Silicone Sealants
Except for being unpaintable, silicone sealants are an excellent all-around choice. These products remain highly flexible and are highly water-resistant. They’re less prone to shrinking than most other sealants and adhere to almost any material. The main downside is their higher cost, but they’re invaluable for creating water and air barriers.
### Polyurethane Sealants
For a tough sealant that bonds nearly everywhere, a polyurethane-based sealant could be the best option. These sealants create strong bonds between materials and seal joints to prevent fluids and other substances from passing through. They’re also abrasion-resistant and offer more flexibility than many other sealant types. Polyurethane sealants come in tinted colors like gray, black, or white to match or complement surroundings.
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