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Best Caulk for Sealing Skylights

Best Caulk for Sealing Skylights

What is the best caulk for sealing skylights? Sealing skylights is a crucial task that often goes overlooked, leading to a host of problems such as leaks, condensation, and even structural damage over time. While there are various types of sealants available in the market, silicone stands out as the only recommended option for this specific application. In this article, we’ll delve into the importance of using silicone as your go-to sealant for skylights, how to apply it both from the outside and inside, and answer some frequently asked questions about skylight sealing.

Should You Caulk A Skylight?

Absolutely, caulking a skylight is not just an option; it’s a necessity. Skylights are prone to leaks, especially during heavy rain or snow. Water can seep through the smallest gaps, leading to moisture buildup and, eventually, water damage. Moreover, poorly sealed skylights can result in energy loss, increasing your heating and cooling bills.

So, why is silicone the best choice for this task? Unlike other types of sealants, silicone offers superior weather resistance, ensuring a long-lasting seal. It also provides excellent adhesion to various materials, including glass and metal, commonly used in skylights. Most importantly, silicone can withstand UV rays, which is crucial given that skylights are constantly exposed to sunlight.

Not only should you caulk your skylight, but you should also make sure to use silicone sealant for the best results.

Why is Silicone the Best Caulk for Sealing Skylights?

When it comes to sealing skylights, not all caulks are created equal. Various types of sealants like polyurethane, acrylic, and butyl are available in the market. However, silicone sealant is the undisputed champion for this specific application. Here’s why:

Weather Resistance

Silicone sealants are known for their ability to withstand extreme weather conditions. Whether it’s scorching heat or freezing cold, silicone maintains its elasticity, ensuring a durable seal.


Silicone sealants offer long-lasting adhesion, reducing the frequency of reapplication. This durability makes it a cost-effective choice in the long run.

UV Protection

Skylights are constantly exposed to sunlight, making UV resistance a critical factor. Silicone sealants offer excellent UV protection, preventing the material from breaking down over time.

How to Choose a Silicone Sealant

When selecting a silicone sealant, look for one that is specifically designed for outdoor use and offers high water resistance. Additionally, consider the sealant’s curing time and whether it is paintable if you plan to paint over it.

In conclusion, for sealing skylights, silicone is the only sealant that checks all the boxes for weather resistance, durability, and UV protection.

Silicone Sealant for Skylights

How to Seal a Skylight from Outside

Sealing a skylight from the outside is a straightforward process, but it requires attention to detail to ensure a watertight seal. Here’s how to do it using silicone sealant:

Preparing the Surface

Before applying the sealant, make sure the area around the skylight is clean and dry. Use a putty knife to remove any old caulk or debris. Wipe the surface with a solvent to remove any residual oils or dirt.

Applying the Silicone Sealant

Load your caulk gun with the silicone sealant and cut the nozzle at a 45-degree angle. Start at one corner and apply a continuous bead of sealant around the skylight, ensuring that you cover all gaps and seams.

Ensuring a Watertight Seal

Use a caulk smoothing tool or your finger to press the sealant into the gaps, creating a watertight seal. Wipe away any excess sealant with a damp cloth.

Additional Tips

  • Always wear safety gear, including gloves and eye protection.
  • Check the weather forecast before starting; silicone sealant should be applied in dry conditions.
  • Allow the sealant to cure for at least 24 hours before exposing it to water.

By following these steps, as a homeowner you can effectively seal your skylight from the outside, ensuring it remains leak-free and energy-efficient.

Sealing a Skylight from Inside

Sealing a Skylight from the Inside

While sealing a skylight from the outside is crucial for preventing leaks, it’s equally important to seal it from the inside to ensure optimal energy efficiency and comfort. Here’s how to go about it using silicone sealant:

Safety Measures

Before you begin, ensure you have a stable ladder to reach the skylight. Always wear safety gear, including gloves and eye protection.

Application Techniques

  1. Clean the Area: Use a putty knife to scrape off any old caulk or paint around the skylight. Clean the surface with a solvent to remove any oils or residues.
  2. Apply the Sealant: Load your caulk gun with silicone sealant. Cut the nozzle at a 45-degree angle for precise application. Apply a continuous bead of sealant around the interior edges of the skylight.
  3. Smooth the Sealant: Use a caulk smoothing tool or your finger to smooth out the sealant, ensuring it fills all gaps and creates a watertight seal.
  4. Wipe Excess: Use a damp cloth to wipe away any excess sealant immediately.

Additional Tips

  • Make sure the area is well-ventilated, as silicone sealant can emit fumes.
  • Allow the sealant to cure for at least 24 hours before subjecting it to any stress or moisture.

By taking the time to seal your skylight from the inside, you not only prevent potential leaks but also improve the overall energy efficiency of your home.

Can You Use Flex Seal On A Skylight?

Flex Seal has gained popularity among DIYers for its ease of use and versatility. However, when it comes to sealing skylights, Flex Seal falls short in several key areas, making silicone the superior choice. Here’s why:


Silicone sealants offer excellent adhesion to a variety of construction materials commonly used in skylights, such as glass and metal. Flex Seal, on the other hand, may not provide the same level of adhesion, especially under extreme weather conditions.


Silicone is known for its long-lasting durability. It can withstand the test of time, resisting shrinkage and peeling. Flex Seal is less reliable in terms of service life and may require frequent reapplication.

UV Resistance

Skylights are exposed to constant UV rays, and silicone sealants are formulated to resist this exposure. Flex Seal lacks this essential feature, making it less suitable for skylight applications. After a few months of UV exposure, it will likely shrink, leaving holes around the seal.

Flex Seal for Skylights

Water Resistance

When it comes to creating a waterproof seal, silicone is unmatched. It offers a watertight seal that can withstand moisture and prevent condensation around the skylight lens. Flex Seal may not offer the same level of water resistance, making it less reliable for preventing roof leaks. 

Professional Roofing Standards

Silicone sealants meet the requirements and standards set by professional roofing companies. Flex Seal is more of a general-purpose product and does not adhere to these specialized standards.

In summary, while Flex Seal may be a convenient option for some home improvement tasks, it is not recommended for sealing skylights. Silicone remains the go-to product for ensuring a durable, weather-resistant, and watertight seal.

How to Seal a Roof Around a Skylight

Sealing the roof around a skylight is just as important as sealing the skylight itself. A poorly sealed roof can lead to water seepage, causing damage to the roofing shingles and even the attic. Here’s how to properly seal the roof around a skylight using silicone sealant:

Preparing the Roof

  1. Inspect the Area: Before you begin, inspect the roof shingles and siding around the skylight for any signs of damage or wear. Replace any damaged shingles.
  2. Clean the Surface: Use a putty knife to remove any old caulk, roofing cement, or debris. Clean the area with a solvent to ensure optimal adhesion.

Applying the Silicone Caulk

  1. Load the Caulk Gun: Insert the silicone sealant into your caulk gun and cut the nozzle at a 45-degree angle.
  2. Seal the Shingles: Apply a bead of silicone sealant under the edge of the shingles that overlap the skylight. Press the shingles down to ensure a good bond.
  3. Seal the Siding: If your skylight is close to the siding, run a bead of silicone along the joint where the skylight meets the siding to seal the gap.

Ensuring a Watertight Seal

  1. Smooth the Sealant: Use a caulk smoothing tool to press the sealant into the gaps and create a watertight seal.
  2. Check for Holes Around the Seal: Inspect the sealed area for any missed spots and apply additional sealant as needed.

Additional Tips

  • Always check the manufacturer’s guidelines for the recommended curing time.
  • Avoid sealing the roof in extreme weather conditions to ensure the sealant cures properly.
  • If you’re not comfortable performing this task, consider hiring a professional roofing company for best results.

By taking these steps, you can effectively seal the roof around your skylight, ensuring long-term durability and water resistance.

Frequently Asked Questions

Can You Paint Over Silicone?

While silicone sealants offer many advantages, they are generally not paintable. If you plan to paint over the sealant, look for a paintable silicone or use a primer specifically designed for silicone surfaces.

How Often Should You Reapply Silicone Sealant?

Silicone sealants are known for their durability and long-lasting adhesion. However, it’s a good idea to inspect the sealant annually for any signs of wear or peeling. Typically, a high-quality silicone sealant can last up to 10 years.

Is Silicone Sealant Safe for All Types of Skylights?

Silicone sealants are versatile and can be used on various types of skylights, including those made of glass, plastic, or metal. However, always read the manufacturer’s guidelines to ensure compatibility.

Does Silicone Sealant Allow Water to Pass?

No, silicone sealants create a watertight seal, making them ideal for preventing leaks and water seepage.

What About Mold and Mildew?

Silicone sealants are generally resistant to mold and mildew, making them a good choice for areas prone to moisture, such as around skylights.

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