Heavy Duty Silicone vs. Top Coat Silicone
When and Why to Use Each
Quick take: Heavy Duty Silicone is for problem areas like seams, penetrations, larger cracks, and vertical transitions. Top Coat Silicone is for full roof coverage and long-term protection. Use them together for best results.
Understanding High-Solids Silicone
Both Heavy Duty Silicone and Top Coat Silicone are 100 percent high-solids coatings, meaning most of the material you apply remains after curing. This helps them resist ponding water, UV rays, and weathering better than lower-solids coatings or water-based coatings that can wash away over time. Because they share the same base chemistry, they both form a seamless, waterproof membrane and cure quickly, with a tack-free surface in about one to two hours.
What makes high-solids coatings different
- High solids means very little solvent flashes off during curing, so you get a thicker finished film. Acrylic and other water-based coatings can flash off 40 percent or more during curing, meaning you may need multiple coats to get the same result.
- 100 percent silicone allows the cured membrane to remain flexible and maintain its properties through heat, cold, and exposure.
- Both coatings are suitable for direct exposure to ponding water and sunlight.
Why Heavy Duty Silicone Exists
When your roof has unusual details like large cracks, fasteners, seams, penetrations, or vertical surfaces, Top Coat alone is not enough. Heavy Duty Silicone is designed specifically for these problem areas.
Our Heavy Duty coating is a thick, high-build liquid dispersion of 100 percent silicone rubber designed to seal abnormal roof penetrations that cannot be covered with Top Coat Silicone. It features low odor, superior adhesion to many substrates, and can be applied with a brush, trowel, or putty knife.
Heavy Duty Silicone is closer to a caulk than a typical roof coating. It is viscous enough to be applied on vertical surfaces or even on the underside of horizontal surfaces without dripping or sagging. Because of its thickness, it can bridge gaps and stay where you put it, making it ideal for prepping seams, cracks, and penetrations before applying Top Coat over the whole roof.
Key characteristics of Heavy Duty Silicone
- Thick, caulk-like consistency that remains in place on seams, joints, and vertical surfaces
- Designed for irregular penetrations like vents, larger cracks, skylights, chimneys, and complex flashing details
- Applied by trowel, putty knife, or brush, not rolled on
- High-solids and low VOC, about 94 percent solids by weight
Top Coat Silicone: Full Roof Protection
Once your seams and penetrations are sealed with Heavy Duty Silicone, you can coat the entire roof with Top Coat Silicone. Top Coat is thinner and designed to roll or brush onto large surfaces. It levels out to form a uniform membrane across the roof, restoring most substrates in a single application.
Because Top Coat is less viscous, it is easier to spread over big areas. It cures quickly, with a tack-free surface in one to two hours, and creates a seamless, watertight barrier. For most residential and light commercial roofs, Top Coat adheres well without primer, though an adhesion promoter may be recommended for some RV and camper roofs.
How to Use Heavy Duty Silicone on RVs
Seams and joints
RVs have many seams where panels meet, along with lap joints and fasteners. These joints flex when driving and are prime leak points. Heavy Duty Silicone’s thick, caulk-like consistency fills these seams and stays put.
- Clean and dry the area. Remove any loose caulk or debris.
- Apply Heavy Duty Silicone across seams and around the perimeter of the RV roof, making sure it feathers onto the surrounding surface.
- Because the product is high-build, it stays in the joint rather than running down the side of the RV.
- For gaps wider than 1/4 inch, insert backer rod to control joint depth, then apply a heavy coat of Heavy Duty Silicone.
- Allow the silicone to cure, typically 24 to 48 hours. Once fully cured, apply Top Coat over the entire roof for a uniform finish.
Penetrations and vents
Around vents, skylights, air conditioners, and antenna bases, there are often complex shapes, bolts, and flashing details that are hard to seal with a roller. Heavy Duty Silicone can be worked into corners and up vertical surfaces without sagging.
- Check for movement. If there is significant flexing in the vent, skylight, etc., make sure the object is securely fastened and all bolts/screws are in good working order before coating. If all is in good working order, you can apply Heavy Duty Coating liberally around the flashing as long as it is clean and dry.
- For underside and overhang areas, Heavy Duty Silicone can adhere and cure without dripping. Apply carefully to avoid spills.
Stress cracks and larger gaps
Not all cracks are the same.
- For cracks smaller than 1/4 inch, apply a heavy coat of Heavy Duty Silicone to patch the crack.
- For cracks larger than 1/4 inch, use backer rod first, then apply Heavy Duty Silicone over the joint so it is filled and supported before you topcoat.
Beyond RVs: Other Applications
While RVs are a clear use case, Heavy Duty Silicone can be used anywhere there are complex roof details and leak-prone transitions.
Homes and mobile homes
- Chimneys and skylights: Seal around masonry or metal bases, then topcoat with silicone to create a continuous waterproof membrane.
- Wall-to-roof transitions: Apply Heavy Duty Silicone along vertical transitions where water can infiltrate and where a brush-grade coating might sag or run.
- Parapets: Seal joints and seams on parapet walls, then coat the wall surface with Top Coat for uniform protection.
Low-pitch and flat roofs, including commercial roofs
- Seams on metal roofs: Encapsulate fasteners and seams with Heavy Duty Silicone to help prevent leaks.
- Roof penetrations: Seal around HVAC curbs, plumbing vents, and roof hatches before coating the rest of the roof with Top Coat. Heavy Duty Silicone’s ability to adhere to vertical and underside surfaces reduces the chance of sagging or running during application.
Specialty uses
- Mobile homes and travel trailers: These structures often have thin metal roofs with many seams. Heavy Duty Silicone is ideal for sealing seams and helping prevent leaks.
- Structures with irregular shapes: Domes, barrel roofs, and irregular additions benefit from the product’s ability to bridge gaps and adhere to non-horizontal surfaces.
- Industrial equipment: Seal around rooftop machinery, ductwork, and anchor points before applying a full roof coating.
Practical Tips for Application
- Adhesion tests: We always recommend doing an adhesion test prior to coating to ensure your roof is a good candidate for silicone. Perform an adhesion test on one or two areas to confirm the surface is ready.
- Surface preparation: Ensure surfaces are clean, dry, and free from oils or contaminants. Power wash or degrease as needed, then allow to dry completely.
- Application: Use a trowel, putty knife, or stiff brush to apply the Heavy Duty Silicone. Overlap each pass slightly. For vertical surfaces, apply from the bottom up to reduce drips.
- Cure times: Heavy Duty Silicone develops a tack-free surface within one to two hours and cures through about 1/8 inch depth in 16 to 18 hours. Protect the repair from rain or debris until it has skinned over.
- Top coating: If you want full-roof protection, apply Top Coat Silicone after the Heavy Duty Silicone has cured. This creates a seamless finish and helps ensure UV protection across the roof surface.
Conclusion: Choose the Right Tool for Each Part of the Job
Our Heavy Duty Silicone and Top Coat Silicone are complementary products. Use Heavy Duty Silicone for difficult areas like cracks, seams, penetrations, and vertical transitions where a thick, high-build material is required. Then use Top Coat Silicone over the entire roof to create a uniform, durable membrane. Both are 100 percent silicone and high solids, so you get long-lasting protection from ponding water and UV radiation.
By understanding the strengths of each product, you can restore and protect not only RV roofs but also residential, commercial, and mobile home roofs with confidence. When in doubt, test a small area first and always follow proper surface preparation and curing guidelines.
If you have questions about your specific project or want help choosing the right product, contact us here. We are here to help you succeed.