3M 4200 vs. 5200 Underwater Sealant: Stop Any Leaks

Believe it or not, but there was a time when underwater sealants did not exist. The underwater bonding industry had trouble finding a high-quality solution, which is why 3M stepped up and offered the best solution.

You may find yourself in hard times of searching for the best sealant. 3M 4200 vs. 5200 underwater sealant; which one do you prefer? As a boat owner, you know that it’s essential as there might be instances that need to cover up cracks, leaks, or dents. With a multitude of options in the market, finding a suitable sealant can be a challenge.

To select the best underwater sealant, it is necessary to understand its elasticity, application method, and compatibility. Boaters can misinterpret or incorrectly understand each type and purpose of marine-grade sealant.

4200 vs. 5200; this comparison has narrowed down the best ones you can get, considering each product’s durability, effectiveness as well as more extended service. Thus, you analyze some aspects to find the most suitable one in providing your boat’s needs. Read on to explore these incredible options.

3M 4200 Vs. 5200 Underwater Sealants: Specification Shorty

Before choosing one, it is essential to become familiar with the application method, elasticity, and compatibility factors of underwater bonds. Obviously, correct information helps you to make the right decision.

3M 42003M 5200 
Bottom/Topside Fiberglass, Wood, Metal, Some Plastics, Above and Below Water; Not For Acrylics Abs or LexanBottom/Topside Permanent Bonding Above and Below Water. Extremely Strong and Flexible
3 Ounce Tube10 Ounce Cartridge
Tack-Free: 2 Hours; Complete Cure: 24 HoursTack-Free: 2 Hours; Complete Cure: 5-7 days
One-Part Adhesive, One-Part SealantOne-Part Adhesive, One-Part Sealant
300 psi700 psi
Paintable and SandablePaintable
Medium pasteMedium paste

3M 4200 Vs. 5200 Underwater Sealant: In-Depth Comparison

Applying Materials

3M 4200:

The 3M 4200 polyurethane sealant is a one-part general-purpose sealant that adheres well to most surfaces, including wood, fiberglass, gel-coat, plastic, and metal. After curing, 4200 forms a watertight, weather-resistant seal on boat hardware at and below the waterline.

3M 5200:

A 3M 5200 underwater sealant will seal seams, fittings, housing, and portholes below the water-line, as well as on boat hulls, decks, and fittings. A crack in the deck, hull, or stem joint of your boat can be repaired with this material, and the results are excellent.

Underwater Ability

3M 4200:

You can use marine products to seal gaps, seams, and joints, depending on how they are applied. It is essential to know how to apply them so you can determine whether they are submerged, underwater, or applied dry. However, considering these factors, especially the application method, is crucial.

3M 5200:

Despite spending a week curing, the underwater sealant remained unchanged. Leaving it exposed to direct sunlight or underwater will surprise you at how tough it is. For boaters, this product will be a great way to bond and seal their interior and exterior fixtures together.


3M 4200:

Basically this product was created for longer lasting durability. Hardware and bedding applications are ideal for this material. Paintable and sandable, it can be used for a variety of purposes. Many of them are found in underwater caulk and underwater boat sealants, which is understandable

3M 5200:

This adhesive is suitable for repairing cracks, holes, and dents in fiberglass, wooden surfaces and metal. This sealant works better on fiberglass for boats because it is flexible with a permanent bond. Polyurethane polymer’s long-lasting formulation, marine environments, saltwater, and adverse weather conditions are resistant to its effects.


3M 4200:

  • Disassembly is possible with marine bonding of medium strength.
  • This formula quickly provides tack-free results in just one hour and typically cures in 24 hours.
  • This adhesive is flexible and durable and can be applied above and below the waterline.
  • Due to its medium strength, which allows disassembly also. It’s capable of being painted and sanded. 

3M 5200:

  • Suitable for wood, fiberglass, metal, and RV surfaces, ensures that boat and RV mountings are permanently sealed and bonded.
  • Formulated for boats and RVs, easy to apply without mixing. Strong bonds are formed between sturdy polyurethane polymers.
  • This adhesive can fix dents, cracks, metal, gaps on fiberglass and wooden surfaces.

Benefit of Using

3M 4200:

  • It is ideally suited for rub-rails, deck fittings, stern joints, and access plates.
  • It makes it ideally suited for large surface area applications that require several hours of open time.
  • Strong bonds and flexibility above and below the waterline. It’s durable and flexible material that absorbs vibrations, shocks, shrinking and swelling structural movements.

3M 5200:

  •  This exceptionally strong adhesive sealant is suitable for both above and below water-lines and offers extended working hours.
  • Sealant made of polyurethane that resists movement, weathering, direct sunlight, and saltwater.
  • Suitable for withstanding vibrations, swelling, shrinking, and shocks.

Key Reasons You Should Consider Sealants 

When you install hardware on a sailboat or powerboat, you reach for a tube of 3M 4200 or 3M 5200. Usually, this product is used as a sealant against moisture. Due to its adhesion properties, this product strengthens the bond between two parts. However, why do you use a sealant?

A boat’s underwater sealants keep it functional and clean, as well as offer these advantages:

  • Marine sealants are an ideal way to keep a boat watertight, airtight and give it a longer lifespan.
  • Protects vessels against external and marine environmental damage by providing durability, stability, and resilience.
  • You can get boating protection that’s easy to use at your local retailer.
  • Comparing hiring a professional with doing the work yourself can save you time, money, and resources.
  • Enhanced product quality, design flexibility, and performance.
  • Reduced manufacturing costs, Enhanced Product Aesthetics, and Improved Process Productivity.

Typical Bonding And Sealing In Recommended Applications Include

Using 3M Adhesive/Sealant 4200 or 5200 will enable you to disassemble wood, fiberglass parts bonded together. If a permanent bond is desired, you shouldn’t hesitate to use a 3M underwater sealant. 

  • Wood to fiberglass -Portholes
  • Deck fittings 
  • Fiberglass deck to the fiberglass hull
  • Rub-rail attachment
  • Stanchion supports
  • Trunk joints
  • Between struts and planking
  • Sealing screw-holes
  • Moldings
  •  Some plastics (test before assembly)
  •  Metals 
  •  Glass

Which one is better than the others?

Compared to 3M 5200, the 4200 sealant has approximately half the strength, making it an ideal choice for applications where the bond may need to be broken later, such as replacing hardware. A sealant or caulk should be marine-grade and top quality as well.

Hence you would know if the formulated solution can work well with your boat materials and conditions.


STOP! It would be best if you thought about which bedding compound you should be using before installing new hardware or sealing up that piece of equipment. For example, 3M 4200 is different from 3M 5200. Make sure there isn’t a large space between the deck and the part.

The 4200 will accumulate dirt fairly quickly and is somewhat difficult to clean. Therefore, if you want your boat to look nice, only apply a small amount of 4200. If you use the wrong material, you could have a very tricky time in the future!


Before spending your money on the wrong underwater sealant, you need to ask yourself many questions.

Can You Use Sealant Without A Gun?

The quick answer to this question is yes. You can apply caulk without a gun. However, this requires a lot more effort and care than caulking with a gun. You can do it easily with hand pressure, but using a caulking gun decreases the risk of making a mess.

What Do Sealants Do?

Two or more surfaces are sealed with sealants to keep out water and air. Sealants are frequently used as adhesive bonds (usually accompanied by mechanical fasteners); others are used to isolate surfaces against electrolysis, noise or vibrations.

What Does Waterproof Sealant Do?

Waterproof sealant is an invaluable product used in both sealing the exterior of your home from the elements and protecting high water areas inside your home from damage.

Final Word

You already know about 3M 4200 vs. 5200 underwater sealants but are confused; how would you rate them? In my experience, 4200 and 5200 treat the same, although the latter cures faster. According to my experience, 5200 has greater adhesive properties and, as such, is more “permanent.” This 3M 5200 fiberglass sealant, without a doubt, it’s the best buy. It is easy and quick to apply, so you would not want to miss it.

Whenever a fiberglass hull is to be penetrated, including through-hull attachments, I always use 4200 or 5200. Those products do precisely what I need: they easily adhere, keep the water out, remain flexible, but can be removed without a lot of effort.

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