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Best Marine Sealant – All You Need to Know About Underwater Boat Sealant

Being a boat owner, the thing that would bother you the most will be the wellness of your beloved boat. Any cracks, dents, or leakage issues can cause you to stress out. The best way to fix the loopholes and get it back to its proper functioning is by applying a boat sealant. 

What is a marine sealant?

A sealant, in a generic sense, is a product that is used to restrict any unwanted passage of fluids. But if you want to use it for your boat, you need a sealant that works even in water. So is there any sealant that can be applied underwater? Well, obviously! Marine sealants are specially designed for boats. It is a substance used to block the openings of the cracks, dents, or leakage areas, be it on the surface, joints, or any other opening areas on the boat. It is basically a savior for your water-vehicle.

How to apply the marine sealant or caulk?

Applying a sealant is considered quite a task, but it may necessarily not be so difficult. Here are some easy steps on how to apply marine sealant.

Step 1: If you already have a caulk there, reef it off with a tool. 

Step 2: Remove the residue.

Step 3: Mask the borders with the tape in order to keep it clean. 

Step 4: Cut the tip of the sealant appropriately, neither narrow or wide.

For neater results, use the caulking gun. Don’t pull; just push. And you are done with it!

Best Marine Sealants

Selecting the best marine sealant is not easy when you have countless options available in the market. You might always feel baffled while doing so. Don’t bother – we are here to help you with taking the final call. This article contains a top-five marine sealant that is readily available in the market.

1. 3M Marine Adhesive Sealant 5200

3M Marine Adhesive Sealant 5200

If you are unable to find the definite answer to which marine sealant is best, your search has just ended. The 3M marine sealant 5200 is the perfect fit. Its users term it as the “most trusted sealant” for more than 50 years now. It is the gap-filling polyurethane most suitable for wood gel coat and fiberglass. 

Pros
  • It is capable of curing fast. You can get your boat back in the water in a day or two.
  • It won’t crack or peel and is ensures long-lasting formula and flexibility.
  • It proves to be the superb marine sealant above and under the waterline.
  • It is known for its strong bond, even dring vibrations, swelling, shrinking, or shock.
  • It is less expensive. The company offers it at a low price.
  • It is your boat’s savior that is easy to apply.
Cons
  • Cleaning it up is a bit difficult because of its robust elements.
  • It is not so ideal for huge sealing jobs as it will take a lot of your time.

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2. 3M Marine Adhesive Sealant 4000UV

3M Marine Adhesive Sealant 4000UV

If you are wondering which marine sealant is best below the waterline, 3M Marine Adhesive Sealant is the answer. 3M Marine Adhesive Sealant is a one-component marine grade sealant that provides medium strength. It is a gap-filling adhesive sealant. It cures to form a firm, flexible, and waterproof bond. It works well above and below the waterline.

Pros
  • It gives high performance and allows disassembly.
  • Excellent V resistance ensures long term performance.
  • It gives you a stable color sealing as it does not crack, peel, or shrink.
  • This boat sealant is most suitable for aluminum, gel coat, wood, and fiberglass.
  • It is the weather, saltwater, and stresses resistant caused by joint movements.
  • It can be removed if repair is necessary and is paintable immediately after its application.
Cons
  • It flakes off paint immediately
  • The plastic cap does not go with the tube

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3. Dap Auto/Marine SealantDap Auto/Marine Sealant

Unlike other marine sealants, Dap Auto/ Marine sealant has an easy application process, and cleaning it up is quite easier. It is made up of Silicone runner, which is a synthetic polymer compound. It consists of properties such as being UV resistant and heat resistant. Not only that, but it is also an excellent insulator.

Pros
  • This product is durable and long-lasting. You don’t need to worry about it for years!
  • It is easy to use. Also, it remains water-resistant and weather-resistant.
  • It is clear and resists vibration, expansion, and contraction.
  • It is recommended for both small and comparatively big sealant jobs.
  • The marine sealant offers good value for money and is very trustworthy.
  • Its 100% silicone rubber seals and bonds work best for automotive and marine maintenance.
Cons
  • The packaging is not so made up or appealing.
  • Dap Auto/Marine Sealant has a poorly made screw cap.

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4. 3M Marine Adhesive Sealant Fast Cure 4200

3M Marine Adhesive Sealant Fast Cure 4200

When you wish to make a tough choice for your boat, 3M Marine Adhesive Solvent Fast Cure 4200 makes the best match. It is a robust and semi-permanent sealant. It consists of a flexible Polyurethane for bonding and sealing. It takes 50 to 90 minutes to become tack free. It is a multipurpose adhesive sealant that creates an ideal waterproof seal.

Pros
  • It is ideal for use on wood, glass, fiberglass, many metals, and plastics.
  • In 24 hours, it cures fully, and you get your boat back into the water.
  • It enables structural movement. It resists salt water, weather, and temperature extremes.
  • It allows you to disassemble parts after long term use without damage.
  • This sealant is recommended to use on areas which are shielded from the sun
  • It is also ideal for joints, rub-rails, access plates, and other areas shielded from the sun.
Cons
  • It requires the use of gloves as it is a bit messy to deal with.
  • Some users claimed that the plastic nozzle comes with the sealant is not reliable.

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5. 3M 05206 Marine Adhesive/Sealant

3M 05206 Marine Adhesive/Sealant

3M Marine Adhesive Sealant is a one-component and high-strength adhesive. It works great because of its moisture-curing and gap-filling abilities. It uses polyurethane for permanent bonding of wood, gel coat, fiberglass, etc. and cures to form a firm, rubbery, waterproof seal. You can use this sealant to repair joints and boat hardware. The marine industry trusts this product for more than 50 years.

Pros
  • It is capable of retaining strong bonds during vibration, swelling, shrinking, or shock.
  • This product claims to provide permanent bonding – above and below the waterline.
  • It offers excellent resistance to weathering and saltwater. Thus, It is ideal for the marine.
  • Its tough and flexible polyurethane polymer forms strong bonds.
  • This sealant offers extended working time for attaching and assembling.
  • It cures any damages within 5 to 7 days. The adhesive/sealant becomes tack-free in 48 hours.
Cons
  • One user used it on his canoe and it peeled right off even after allowing it time to set.
  • 3M 05206 Marine Adhesive/Sealant dries very slowly.

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The Bottom Line

Now that you have read the article, you are aware of the basics that;

  1. A marine-grade sealant is a substance that is used to stop the passage of fluids.
  2. Waterproof sealant is essential if your boat has cracks, dents, or leakage at any place.
  3. You need to apply a marine sealant to marine plywood if it has cracks or leakage.
  4. It takes from about 90 minutes to a day to apply the sealant. The time keeps varying as per the type of the sealant being used. 
  5. For metals such as aluminum, flex seals prove to be the right choice.

These are the best marine sealants according to our research and experiences. We are unable to choose one, but as many people have asked us which marine sealant is the best for us, we generally recommend 3M Marine Adhesive Sealant. Don’t stress up if your boat has a leakage. Just go through this article and order the sealant to get your boat back in action. We hope we were of some help to you. Stay tuned for more such updates. 🙂

Tracie Kaneshiro

Hi there! I am Tracie Kaneshiro from Ohio. Having spent most of my life in boats with my dad, I picked up many useful tips from him about their maintenance and care. Through this blog, I am sharing my expertise with all my fellow boat enthusiasts. I hope you benefit from my posts. Thank you for stopping by!

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