Roofing tar and silicone coatings are common options for flat or low-slope roofs, each with distinct performance profiles. This article compares tar-based roof coatings, including asphalt and coal tar products, with silicone roof coatings, focusing on longevity, installation, maintenance, cost, and environmental impact. Homeowners can use this analysis to select the coating that best fits climate, roof condition, and budget.
Overview Of Roofing Tar
Roofing tar coatings are derived from asphalt or coal tar and have long been used to seal asphalt roofs, built-up roofs (BUR), and modified bitumen systems. They form a waterproof barrier when applied as a hot or cold liquid, followed by curing to a flexible film. Tar coatings are typically favored for low-slope surfaces with minor surface irregularities. They offer rapid repair capability and can be applied on relatively short notice.
Key characteristics: high initial waterproofing potential, good adhesion to rooftop substrates, and relatively low material cost. They can become brittle in cold weather and may require more frequent maintenance in regions with intense UV exposure or weathering.
Overview Of Silicone Roof Coatings
Silicone roof coatings are elastomeric, UV-stable, and highly resistant to ponding water. They are applied as a liquid that cures into a seamless, flexible membrane. Silicone coatings are compatible with many roof types, including BUR, single-pply membranes, and metal roofs, and are known for their long service life and low maintenance.
Key characteristics: excellent UV resistance, strong weathering performance, breathable without allowing moisture infiltration, and typically long lifespans with annual inspection. They can be more expensive upfront but often yield lower lifecycle costs due to durability and fewer recoats.
Durability And Longevity
Tar-based systems rely on a dense, waterproof film that can endure moderate temperature swings but may degrade under prolonged UV exposure unless protected by a reflective top coat or gravel ballast. Regular reapplication is common every 5–10 years depending on climate and roof traffic. In some climates, tar can soften in heat and crack with temperature fluctuations.
Silicone coatings demonstrate exceptional longevity in exposed conditions, with many systems rated for 15–20 years or more under proper preparation. They resist UV, ozone, and chemical exposure, reducing degradation over time. However, silicone can be compromised by improper surface prep or contamination, and recoats may be required to maintain reflective properties and waterproofing.
Application And Maintenance
Tar coatings are often applied as a thermoplastic or cold-applied liquid, requiring skilled labor to ensure even coverage and proper bonding. Surfaces must be clean, dry, and primed to maximize adhesion. Tar is less forgiving of surface imperfections and may require primer or patching for leaks. Maintenance commonly involves annual inspections and re-sealing vulnerable seams or details.
Silicone coatings require rigorous surface preparation: removing dirt, grime, and existing coatings that could impede adhesion. A compatible primer or bonding agent is typically used. Application is commonly done with squeegee and roller methods or spray equipment, depending on the product. Maintenance involves periodic inspections, remineralization of exposed areas, and wash-downs to preserve reflectivity and prevent dirt buildup.
Cost And Value
Initial material costs for tar coatings are generally lower than silicone, making tar attractive for budget-conscious projects or emergency repairs. Labor costs may be similar if trained workers are required for application and surface preparation. Over the lifespan, tar may incur higher maintenance frequency and more frequent reapplications, increasing total cost.
Silicone coatings tend to have higher upfront costs but offer longer intervals between recoats and lower maintenance demands. They often provide energy savings through high solar reflectivity, which can reduce cooling loads in hot climates. The lifecycle cost of silicone can be competitive when considering energy savings and longer service life.
Energy Efficiency And Environmental Considerations
Tar-based coatings can absorb solar heat, especially darker asphalt formulations, contributing to higher roof temperatures and increased cooling loads. Reflective top coats or lighter tar blends can mitigate some heat absorption, but energy benefits are typically less pronounced than those of silicone in many climates.
Silicone coatings frequently offer high solar reflectance (cool roof performance), contributing to lower energy usage and better comfort. They are chemically inert and resistant to many environmental pollutants. Environmental considerations also include VOC emissions; modern tar products may include low-VOC formulations, while silicone formulations are often low-VOC as well but depend on the product and installation method.
Best Uses And Considerations
Tar coatings are often chosen for legacy roofs with asphalt or BUR systems that require a straightforward repair or waterproofing layer. They can be effective for temporary fixes or where the structure does not demand high UV stability. Tar can be a practical solution in moderate climates or for budget-driven projects where long-term maintenance is manageable.
Silicone coatings excel on roofs that experience heavy sun exposure, frequent ponding water, or chemical exposure from industrial surroundings. They are well-suited for metal roofs, BUR, and single-ply membranes. Silicone performs best when the substrate is clean, dry, and compatible with the coating chemistry. For roofs with existing elastomeric coatings, compatibility testing is essential to avoid delamination.
Installation Tips And Best Practices
Before choosing a coating, conduct a professional roof assessment to determine substrate compatibility, moisture levels, and local climate impact. For tar coatings, ensure proper surface preparation, including cleaning, priming, and repairing any substrate damage. Apply within the manufacturer’s guidelines to avoid adhesion failures and to maximize sealing performance.
For silicone coatings, perform surface prep to remove laitance, oils, and loose material. Use compatible primers if recommended, apply in suitable weather conditions, and follow recoat windows to maintain performance. Consider reflectivity options to optimize energy savings and evaluate warranty terms based on roof type and climate.
Practical Quick Comparisons
- Durability: Silicone generally longer-lasting; tar may require more frequent maintenance.
- UV Resistance: Silicone excels; tar requires protective measures in sun-heavy climates.
- Energy Impact: Silicone often improves energy efficiency; tar’s impact is variable.
- Cost: Tar lower upfront; silicone higher upfront but potentially lower lifecycle costs.
- Best For: Tar for budget repairs on traditional asphalt/BUR; silicone for UV-rich, ponding, or metal roofs needing long-term performance.
Inspections, Warranties, And Long-Term Planning
Choose coatings backed by solid warranties and documented performance data. Regular roof inspections are essential with either system to catch early signs of wear, pooling, or adhesion issues. For property owners, align maintenance plans with local weather patterns and building usage to maximize return on investment.