The Best Marine Sealants for 2021

Nicholas Swartz
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The best marine sealants for 2021 are very different from those you’d use on the deck of a houseboat or a small cockpit boat.

When talking about epoxies for decks and caulk for boats, I think we need to be clear that we are referring to different products with different properties.

Caulk for stainless, glass, and gel coat boats is absolute junk. But there is one unexpected benefit that shouldn’t be dismissed.

Glass and stainless will support a decent amount of pounds per square inch (psi) without cracking or breaking. Once a boat gets to about 20 feet or so, the structure becomes a little more solid.

Gel coat and paint will crack long before the boat structure fails. Try to push a wood spoon into the caulk on a sailboat’s deck. If it comes out and you’re not bleeding keep pushing. I bet you can take it all the way through the deck to the hull.

Now try that with a boat hull.

I like the idea of this because you can squeeze a long bead into a joint, then do a spot repair on the boat hull without filling the entire area.

I am just not sure you can get a single joint of marine hull caulk out before you hit the brink of a dangerous overdose.

NameCategoryProduct
Dap 00694 2.8-Ounce Silicone Rubber Auto/Marine SealantBest OverallDap 00694 2.8-Ounce Silicone Rubber Auto/Marine Sealant
Gorilla Clear 100 Percent Silicone Sealant CaulkBudget PickGorilla Clear 100 Percent Silicone Sealant Caulk
3M Marine Adhesive Sealant 5200Upgrade Pick3M Marine Adhesive Sealant 5200

1. Dap 00694 2.8-Ounce Silicone Rubber Auto/Marine Sealant

Our rating: 9 / 10

Dap 00694 2.8-Ounce Silicone Rubber Auto/Marine Sealant

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Pros:

  • Very strong adhesive performance
  • Versatile and durable
  • Available in a variety of colors

Dap 00694 Silicone Rubber Auto/Marine Sealant has amazing adhesive performance that is both flexible and resistant to harsh weather conditions. You can use this aerodynamic tube of silicone to close large holes on boats and other vessels and make plans watertight.

The silicone is very strong, but adding more layers for added protection won’t be a problem. You can use it on practically any surface you want. In terms of durability, it is pretty impressive.

The silicone sealant is also very versatile, so you can easily cover up any hole and make your boat watertight. It can be molded, sculpted and tooled for some creative decorative work. This is also a pretty inexpensive option.

2. 3M Marine Adhesive Sealant 5200

Our rating: 9 / 10

3M Marine Adhesive Sealant 5200

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3. Shoreline Marine GOOP

Our rating: 9 / 10

Shoreline Marine GOOP

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Pros:

  • Great at filling small gaps
  • Adheres very well underwater
  • Long-lasting
  • Works well for repairing creases in boat liners

Cons:

  • May need to be sanded and/or re-sealed.

This is a great boat sealant for filling small pin holes and small gaps between hardware. It can also be used to seal creases in boat floor liners. It is not as flexible as other sealants but holds its shape very well and adheres to any smooth surface underwater.

Shoreline Marine GOOP is a two-part silicone sealant. It goes on white but dries very clear allowing you to see exactly where you’ve applied it.

For larger holes or creases in boat liners, you will have to use a lot of GOOP to fill the area to be repaired. For smaller pinholes, you should be able to just fill them right up using the tip of the tube.

4. Gorilla Clear 100 Percent Silicone Sealant Caulk

Our rating: 8 / 10

Gorilla Clear 100 Percent Silicone Sealant Caulk

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Pros:

  • Nontoxic formula
  • Resilient and flexible
  • Easy to remove and is reusable
  • Not messy

Cons:

  • Clogs fast
  • Expensive

Everyone who has used Gorilla Clear has reported that it’s a great sealant to use. It’s a sealant that is purified and odorless. You can use this product after every one or two weeks.

Basically, it’s applied to wood, metal, and most plastics. It’s liquid silicone in an easy to use cartridge that helps in sealing joints and seams. Additionally, you’ll be able to apply it directly on structures and surfaces of vinyl siding, wood, fiberglass, concrete, metal, and ceramic tile.

When using this product, you should be aware that it’s very difficult to remove. You’ll be better off using a different sealant or caulk.

5. 3M Marine Adhesive Sealant 5200FC Fast Cure

Our rating: 8 / 10

3M Marine Adhesive Sealant 5200FC Fast Cure

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Pros:

  • Applicable to various surfaces like fiberglass, metal, wood, and concrete
  • Little or no washing is required
  • Sticks nicely to aluminum, wood, and plastic
  • Its flexible enough to be used on uneven surfaces
  • Suitable for outside and underwater use
  • Not affected by oils, gasoline, and other chemicals.

This 3M marine sealant is applied best with a 0.008 inch bead between joints. This gives maximum water resistance and flexibility.

This glue sealant exhibits excellent strength to temperature exposure thus can withstand the environmental fluctuations weather represents.

The sealant is applied either manually with brush or pneumatic modality.

6. Boat Life Lifeseal Sealant Cartridge

Our rating: 8 / 10

Boat Life Lifeseal Sealant Cartridge

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Pros:

  • 14 different sizes
  • Use on a range of substrates
  • Three mil thickness
  • Outlasts & outperforms other sealants
  • Easy-to-use packaging
  • Environmentally friendly

Cons:

  • Needs to be cut with a knife/utility knife
  • Doesn’t adhere to gravel as well

Our boat can be used for a variety of situations, no matter the weather. The right sealant can keep water out and can create a level of comfort inside your boat.

AquaSeal Boat Life Sealant can be applied according to the following surfaces:

While these are the listed surfaces for application, it is possible that you could use the sealant on materials other than what are listed.

7. STAR BRITE Marine Silicone Sealant

Our rating: 8 / 10

STAR BRITE Marine Silicone Sealant

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STAR BRITE Marine Silicone Sealant and Adhesive is a great product to seal your boat, because it works in all temperatures and it doesn’t allow any water to leak into the boat.

There are many products on the market that claim they are able to seal your boat, but they actually cause more harm and more leaks than good.

STAR BRITE Marine Silicone Sealant and Adhesive is made from EPDM. This is one of the most common types of sealant on the market. EPDM is top notch and provides a lifetime of applying and re-applying and doesn’t require any degreasing right beforehand.

8. Loctite PL Marine Fast Cure Adhesive Sealant

Our rating: 8 / 10

Loctite PL Marine Fast Cure Adhesive Sealant

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Pros:

  • Brush-on sealant …Sealant dries clear
  • Can be used to seal wood and metal
  • Fast cure time; 1-2 hours
  • Sealant resistant to UV light
  • Paintable and sandable with primer
  • Non-flammable

Cons:

  • Has an odor
  • Not water resistant
  • Has to be stored in a cool place

Overall, this Loctite PL Marine Fast Cure Adhesive Sealant has excellent user reviews. It’s used to seal wood and metal and the end result is a clear sealant. You can paint or sand it once it’s fully dry. You can use Loctite PL Marine Fast Cure Adhesive Sealant for all types of wood, not only marine grade wood, giving it an advantage over some other sealants.

Loctite PL Marine Fast Cure Adhesive Sealant, 10.1 Ounce Cartridge is non-flammable and it’s waterproof because it’s fully cured. It has a fast cure time of approximately 1-2 hours. With a brush application you can finish an 8 x 12-inch surface within 15-20 minutes.

9. Amazing GOOP 172012 Eclectic Marine Adhesive

Our rating: 8 / 10

Amazing GOOP 172012 Eclectic Marine Adhesive

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Pros:

  • Easy to apply and dries quickly.
  • Can be used inside your boat to repair leaking holes or cracks, or outside to seal and protect your boat against weather, moisture, vibrations, and scratches.
  • Absolutely will not swell, peel, or rot like other marine adhesives.
  • The best adhesive for yachts, canoes, sailboats, kayaks, and dinghies.

Cons:

  • Needs to use a high-speed drill for best results.
  • Need to tape the outside perimeter to avoid getting any on the surface
  • Will not adhere to some hulls.

If you're looking for a good marine sealant to fix your boat, then this is the sealing agent to use. It is very easy to apply to a wide variety of surfaces, and it will not rot or peel away from your boat.

This adhesive is an excellent water-resistant sealant that will not let water leak through the walls. It works perfectly to seal joints or cracks, and it will ensure that the materials under the adhesive last for a long time.

It will stick to anything you put it on, and it will take a beating and keep going. This sealant is designed to preserve hulls.

10. TotalBoat Seal Marine Sealant

Our rating: 7 / 10

TotalBoat Seal Marine Sealant

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Pros:

  • Can be applied underwater
  • Effective in applications where paint or fiberglass is required
  • Bonds to multiple surfaces
  • It’s UV resistant and Sinkhole Resistant
  • Low VOC

Cons:

  • Can be messy on some surfaces
  • Has a strong odor
  • The price is a bit steep compared to similar products
  • A little on pricey side

TotalBoat Seal is designed to be used when you need to patch, seal, caulk, or bond almost any material in your boat. It is made out of a high-quality rubberized acrylic polymer that prevents water from penetrating and permanently seals leaks.

This product is ideal for a wide variety of applications including but not limited to: laminating, sealing, bonding, fastening, and repair.

The TotalBoat Seal cartridge is a marine grade canister that contains enough sealant to complete a number of tasks: bonding, coating, caulk, sealing, serving, filling, glazing, and serving.

11. 3M Marine Adhesive Sealant Fast Cure 4200

Our rating: 7 / 10

3M Marine Adhesive Sealant Fast Cure 4200

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Pros:

  • Easy application
  • Good product
  • Flexible

Cons:

  • Thin consistency
  • Not very strong

The 3M 4200 is, as advertised, a fast drying sealant. According to the manufacturer, it can reach a cured stage within 15 minutes at 77 degrees Fahrenheit and 50% relative humidity. You’ll have 30 minutes of working time before it gets too stiff and hard to use.

The product comes in a small 3 oz. tube, and a single tube is enough for a couple of small boat jobs or larger jobs you can get away with using a little less. Note that if you’re intending on repositioning the sealant, it must be already cured.

12. Sudbury 300 Elastomeric Marine Sealant

Our rating: 7 / 10

Sudbury 300 Elastomeric Marine Sealant

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Frequently Asked Questions (FAQ)

What is the best marine sealant?

If you are in the market for a marine sealant, you will want to select one which offers the best performance, durability, and ease of application. A good marine sealant will resist UV rays, salt, moisture, and alkalinity, as well as other chemicals and pollutants typically found in marine environments.

Avoid sealants made with silicone, petroleum, or other materials that are not compatible with marine environments. In addition, look for sealants that feature a flexible, brushable or rollable formula, which is less likely to crack or chip than a liquid sealant.

What is the best sealant for an aluminum boat?

If you haven’t considered the option of getting a boat, now is a good time to do so. Boats can be a very fun and worthwhile purchase and are certainly a wise investment.

If you do decide to buy an aluminum boat, though, you occasionally run into issues.

The main issues you may run into with aluminum boats are holes or cracks. If you only have one or two small holes in their hull, it is usually not a big deal. If you have multiple cracks, on the other hand, you probably need to find a solution.

The best marine sealants for aluminum boats will give you a long-lasting fix.

Is there a sealant that can be applied underwater?

For a long time, the only sealants that could be applied underwater were slow-curing silicone sealants and epoxy. Some manufacturers develop new sealants every year that are applied underwater through different techniques, and their properties may differ dramatically from those which are applied above the waterline. In recent years, using special epoxy has become a more preferred method of underwater sealant application because it reacts with wood quickly, and this outdoor-based epoxy requires UV light in order to cure. When applied underwater, use several small blobs of puddy epoxy, and scatter them around the waterline. It can definitely be a challenge to apply these underwater because they can have the consistency of a puddle of play dough. Apply it very thick, leaving it to cure underwater, and hit it with a strong light source. A UV lamp is best for this lighting application.

What is marine grade sealant?

Marine sealants are basically the same product as regular construction grade sealant, but they have been designed to be used on boats. One very interesting feature that sets boat sealant apart from any other is its ability to remain flexible. It doesn't set up like regular construction grade sealant.

This flexibility is paramount to the stability and longevity of a boat.

On a boat, the longer a product can hold its shape, the longer it can resist pressure from external elements. This is why marine sealants are designed to last longer and hold their shape better than most other products.

Conclusion

Marine sealants are ideal for sealing and filling all kinds of components on yachts, and indeed any other boat. You’re looking to seal leaky windows, shafts, or even floorboards. Choosing the best marine sealant for 2021 really depends on where you are in the world.

Our Recommendation

NameCategoryProduct
Dap 00694 2.8-Ounce Silicone Rubber Auto/Marine SealantBest OverallDap 00694 2.8-Ounce Silicone Rubber Auto/Marine Sealant
Gorilla Clear 100 Percent Silicone Sealant CaulkBudget PickGorilla Clear 100 Percent Silicone Sealant Caulk
3M Marine Adhesive Sealant 5200Upgrade Pick3M Marine Adhesive Sealant 5200