The roof – a commonly overlooked aspect of a building – bears the brunt of Mother Nature’s wrath. The relentless sun, the heavy snow, and pouring rain in between, your roof endures it all to keep your living space comfortable and dry. But as tough as it might be, every roof has its limits. Over time, even the best materials start to break down.
That’s why investing in a high-quality waterproofing sealant is essential. These sealants provide an additional layer of defense by filling in cracks and preventing water from seeping through and causing damage. Based on this, with so many products and chemistries available in the market, how do you choose a waterproof sealant that will keep your property safe from leaks for years to come? Continue reading to make the right decision.
What is a Waterproofing Sealant?
Water is a building’s worst enemy if it penetrates the structure. As time goes by, the presence of moisture can lead to mold, mildew, rot, and corrosion, which not only weaken the building materials but can also cause irreparable, long-term damage. A protective membrane averts this by sealing off any cracks, pores, and joints where water might sneak in. When it rains or when water comes in contact with the sealed surface, the water simply slides off or beads up instead of soaking in.
Sealants can be applied to the foundation, roof, walls, joints, windows, and doors, but each area needs a different type of sealant depending on the construction material and the level of water exposure. You can choose from acrylic, silicone, polyurethane, polyether, hybrid, SEBS, and bituminous options based on precisely what you are sealing.
- Flat Roofs: These are quite susceptible to water pooling, so you need a layer with excellent ponding water resistance, like a silicone-based sealant. Silicone is highly flexible, UV resistant, and maintains its integrity under standing water. It can be applied to the seams between roofing sheets to prevent water infiltration. Hybrid sealants have also shown to work well in these conditions.
- Sloped Roofs: Although sloped roofs naturally drain water better, they still require waterproofing around the valleys, ridges, penetrations (chimneys, vents, skylights), and other vulnerable areas. Polyurethane sealants are recommended here because of their strong adhesion to almost all roofing materials (metal, tile, asphalt). Bituminous sealants are used often in these situations as most sloped roof membranes are asphaltic.
- Metal Roofs: Metal roofs expand and contract throughout the year with temperature-based changes, so a flexible sealant like SEBS, polyurethane or hybrid can be an excellent option. These sealants adhere extremely well to metal, resist UV radiation, and remain flexible to handle the thermal movement of metal roofs without cracking.
- Roof Penetrations: A pourable waterproof barrier is perfect on areas around skylights, chimneys, vents, satellite dishes and antennas, solar panels, plumbing vents, rooftop HVAC units, dormers, and roof access hatches to eliminate any risk of leak. These pourable sealers are typically hybrid, polyurethane, or polyether.
- Roof Edges and Eaves: The edges of the roof are defenseless against wind-driven rain and snow. A high-strength hybrid sealant or polyurethane is often used here because it adheres well to various substrates, including concrete, metal, and wood, providing a strong, durable seal that withstands harsh weather conditions.
Why You Need a Roofing Sealant?
The main function of a roof sealer is to block water from entering the underlying structure, extend the lifespan of the roof, and maintain its integrity by keeping out rain, snow, and other precipitation as well.
There are several other benefits of installing a water-repellent roof sealing treatment you may not have thought about:
- It prevents water from getting into even the tiniest cracks, crevices, gaps, and seams that may form in the roofing material over time – regardless of how heavy the rain, snow, or condensation.
- It obstructs water and moisture from creating that damp environment that is perfect for mold, mildew, moss, and algae in the building’s interior.
- It protects the roof from freeze-thaw cycles. In colder climates, any water that does get into small cracks in the roof will freeze, expand, and cause the cracks to widen. A waterproof sealant prevents this from happening.
- It shields the underlying roof deck from rotting or weakening due to water exposure.
- Some sealing compounds also offer UV protection to help the roofing material not break down before their lifespan under the harsh rays of the sun.
- It keeps the insulation dry and in optimal condition, which keeps your more energy-efficient and reduces the heating and cooling costs.
- A hydrophobic roof sealant for metal roof stops water from coming into direct contact with the surface. This is critical in avoiding rust and corrosion.
- It deters the formation of ice dams by ensuring that snow melts and drains off the roof efficiently without seeping into cracks where it can refreeze.
- A high-quality sealing agent keeps the roof’s original color and texture looking newer for longer by fending off any discoloration and staining.
Different Types of Roofing Sealants
If you’re looking for products you can trust, you can never go wrong with Polyglass’ PolyFlash sealants. We have leveraged five decades of experience in the global roofing industry to make sure each waterproofing membrane is designed with you in mind – whether you’re a professional contractor, an architect, or a homeowner. They are all easy to apply, incredibly durable, and made to stand up to whatever nature throws at them.
PolyFlash 1PS – 1 Part Pourable Sealer
PolyFlash 1PS is your go-to solution for sealing all kinds of roof penetrating structures, gutters, pitch pans, metal roof seams, and other tricky areas where water tends to pool. This advanced, one-part hybrid polymer sealer is 100% solids, solvent-free, and permanently elastic, making it incredibly durable across a wide temperature range from -40°F to 200°F.
This pourable sealer reacts with moisture to create a tough, weather-resistant seal that is meant to last in wet, dry, and cold weather conditions. Its ultra-low VOC content and low odor make it a safe choice for environmentally-conscious projects.
PolyFlash HPS – High-Performance Sealant/Adhesive
If strength and flexibility are non-negotiable for your roof, consider this one-component hybrid polymer sealant. PolyFlash HPS doubles as an adhesive to provide exceptional bonding to a wide range of substrates, including asphalt shingles, tiles, modified bitumen, PVC, EPDM, concrete, metal, wood, marble, and vinyl. Just like PolyFlash 1PS, the HPS membrane can also resist ponding water and extreme temperatures (from -40°F to 200°F).
With its fast skin-over time, non-yellowing properties, and quick-setting applicability, PolyFlash HPS is suitable for everything from expansion joints to door thresholds. It’s specially formulated to bond securely, even when the surface is damp.
PolyFlash MPS – Multipurpose Sealant
PolyFlash MPS is the versatile hybrid polymer sealant every roofer should have in their toolkit for residential as well as commercial roofing projects. As the name suggests, this multipurpose sealant is ideal for both moving joints like expansion joints and more static applications such as door thresholds and windowsills. It sticks tightly to almost all types of substrates and performs just as well in freezing temperatures as it does in intense heat. You can count on PolyFlash MPS to deliver a reliable performance across the board. It keeps mold at bay and can be painted over to blend smoothly with any color preference or existing surface.
PolyFlash MPS Clear – Translucent Multipurpose Sealant
When you need a sealant that won’t disrupt the look of your project, PolyFlash MPS Clear is the right solution. This crystal-clear sealant forms an invisible watertight shield around your skylights, windows, or glass roofing. It has all the toughness and flexibility of the original PolyFlash MPS but with the added advantage of being nearly imperceptible once applied. If you’re working with delicate glass, sleek metal, or textured concrete, PolyFlash MPS Clear will enable your skills to shine through without sacrificing the integrity of your design.
PolyFlash Flexible Curb Kit – Universal Roof Penetration Sealing Kit
If you have ever struggled with sealing pipes, vents, solar mounts, and other penetrations, the all-in-one PolyFlash Flexible Curb Kit can make your life much easier. The kit includes PolyFlash HPS (to bond the curb to your roof membrane) and PolyFlash 1PS (to fill the curb and create an instant waterproof seal).
You can shape the elastic, aluminum-reinforced curb by hand – no needs for special equipment or tedious custom cutting. From an intricate plumbing pipe to an oddly shaped electrical conduit, the curb adapts with little to no effort. Installation takes just minutes for both busy contractors and DIY homeowners looking for a foolproof solution. Since it works well with any type of roof inlet or intrusion, you won’t need to stockpile multiple kits for different jobs.
Practical Tips for Choosing the Right Sealant for Your Roof
Match the Sealant to Your Roof Material
You can’t apply the same type of sealant to every surface. For example, asphalt shingles need a bituminous, polyurethane, or hybrid sealant; silicone does not adhere well to asphalt and thus, will peel away over time. Similarly, use EPDM-compatible sealants for your EPDM rubber roof.
Consider Compatibility with Other Roofing Components
When your roof integrates components like solar panels, skylights, or HVAC units, your sealant should not react negatively with the materials involved. Polyurethane sealants are typically compatible with solar panel frames made of aluminum and are safe for use around wiring and electrical components because they do not conduct electricity. With that said, certain silicone sealants may cause plasticizer migration when used on PVC components, which may cause hardening and cracking over time.
Check the compatibility with all materials it will contact, including fasteners, frames, and any adjacent roofing materials. Most manufacturers provide a list of materials their products are compatible with — make sure to consult this or perform a small test patch to avoid long-term issues.
Check for Warranties
Look for products that come with extended warranties — at Polyglass, we offer warranties 30 years and sometimes even more. These warranties should cover cracking, peeling, and loss of adhesion. In addition, certifications like LEED, ASTM C920 (for joint sealants) indicate that the product has undergone rigorous testing to meet industry standards for energy efficiency, movement capability, adhesion, and durability. For commercial projects, compliance with these standards can be critical, especially in jurisdictions where building codes require it.
Plan for Future Re-coating or Re-sealing
If your roof requires re-sealing every few years, choose a sealant that allows for easy re-application without applying a primer or needing to strip away the old material. Silicone sealants, while highly durable, sometimes require special primers when applying over old silicone layers. In contrast, Polyglass’ hybrid sealants allow for quick, no-hassle reapplication without extensive surface preparation.
Factor in the Climate
Sealants with high UV resistance are necessary for roofs in areas with long, hot summers. It’s safe to assume that your roof will endure either extremely hot temperatures or extremely cold temperatures (or both) year after year, so pick a waterproofing membrane with a broad service temperature range (e.g., -40°F to 200°F).
Evaluate Joint Movement Capability
Roofs expand and contract due to changes in the temperature in accordance with the season, which means the joints in your roof or walls will naturally move. Your sealing product should be able to stretch, compress, and flex to accommodate these shifts without cracking or losing its seal.
A recommended joint movement capability is around 25% to 50%. For instance, 35% capability means that the sealant will enlarge/shrink by 35% of the width of the joint it is sealing without breaking and prevent any leaks or gaps from forming over time.
Assess Application Flexibility
If you need to apply the sealant in in winter or wet conditions, polyether or MS polymer sealants are a good choice because they cure well on damp surfaces and don’t bubble or off-gas, which can be an issue with some types of silicone. Cold-applied options are also be effective for humid climates or emergency repairs in sub-zero temperatures, as they remain pliable and adhere well without needing heat for activation.
Prioritize Low VOC and Non-Toxic Options
If you’re handling a roofing project in your home or working as a contractor, ventilation may be a challenge in attics and enclosed spaces. It’s vital to choose a waterproofing sealant with low VOC (Volatile Organic Compounds) and non-toxic properties in these indoor areas. VOCs are chemicals that evaporate into the air during application and release harmful fumes.
A sealant with a VOC content of 50 g/L or lower is generally considered low VOC. Of course, products labeled as “zero VOC”, “ultra-low VOC”, or “solvent-free”, are better. Products certified by GreenGuard, LEED (Leadership in Energy and Environmental Design), Green Seal, and EcoLogo are a reliable way to identify non-toxic products. Polyurethane sealants release isocyanates during the curing process which can have the potential for severe respiratory tract effect on some individuals. Individuals may become sensitized to isocyanates which is the body’s allergy-like response to a substance touched or inhaled.
Do a Small Test Application First
Not every sealant bonds the same way to every roof surfaces. Applying a small amount of the sealant to a corner or less visible spot will help you check how well it sticks and cures. After applying the test patch, give the sealant the recommended curing time, typically ranging from a few hours to a full day. Then see if it spreads evenly without bubbling.
Does it become firm yet flexible without cracking or peeling? The sealant should become solid but remain slightly malleable so it can respond to thermal variations. If you notice poor adhesion, discoloration, or a sticky finish after the curing time, it’s a red flag that the sealant might not be suitable for your entire roof.
Get Long-Term Protection with Cutting-Edge Roofing Solutions from Polyglass
If you are still not sure which sealant is right for you or have any questions, reach out to our friendly roofing experts at Polyglass. We will guide you to the right waterproofing solution based on your roof’s condition, materials, and the local weather. With over 50 years of experience, we lead the industry with self-adhered, high-performance membranes designed for every roofing project, in any budget.