Marine Caulking Vs Silicone: What’s The Difference?

Last Updated on January 11, 2023

If you’ve ever wondered how to seal a boat, you might want to know the difference between Marine Caulking and Silicone. Both are water-resistant, but there are differences between them, including the way they adhere to surfaces.

While all silicones adhere to surfaces, some have better adhesion than others. In testing, 3Ms Marine Silicone proved to be the best choice, with a low odor and a long open shelf life. It also remained workable at room temperature for years, which gives it a long useful life.

Polyether sealant

Silicone and polyether are two different types of adhesives, and one of them has better properties than the other two. Silicone is more rigid and has good adhesion, but silicone has better bonding properties, and polyether has excellent flexibility.

It bonds to wood and metal, and can withstand temperature and weather extremes. Polyether is a good choice for boats, but it is also harsh on other plastics.

While both silicone and polyether are effective, silicone is a better choice for marine applications. The best way to choose between silicone and polyether is by considering the application area.

Silicone is more appropriate for repairs below the waterline, while polyether is more flexible and can be used to repair automotive parts. The differences between silicone and polyether sealants are not as significant as those between silicone and polyurethane.

If you’re looking for a sealant for your boat’s exterior, you may be wondering what the difference is between the two types. While silicone is an inorganic material, polyurethane is a polymer made of organic atoms.

This means that it’s less reactive to UV light than silicone. Silicone is much more resistant to the effects of the sun, while silicone withstands harsh environments.


For many years, polyurethane was the sealant of choice for all sorts of tasks on the water. 3M’s 5200 Fast Cure was a favorite for marine applications, as were Sikaflex adhesives for fiberglass and wood.

However, as time went on, other types of sealants were introduced. Polysulfides are a class of hydrocarbons composed of chains of sulfur atoms. Polysulfides can be synthesized by condensation. Because they’re insoluble in water, they’re not suitable for all areas.

The downside of polysulfides is that they don’t have the same flexibility as silicone. You should avoid using them on parts of your boat that are subjected to flexing, constant vibration, and/or sunlight.

Polysulfides are also sensitive to common chemicals on shipboard. They can take a week to cure and can be painted over. But they’re worth the wait if your plan is to seal teak decks.

Polysulfide sealants are an industry standard in marine engineering and repair. Polysulfides are especially effective in salt water because they don’t lose their integrity, even when exposed to solvents. Pecora Synthacalk GC2+ and TAMMSFLEX SL are two popular examples of polysulfides for marine applications.

These sealants adhere to metal, wood, and masonry with an elastomeric bond. Polysulfide sealants are also resistant to daily temperature changes and have good flex resistance.

Aluminum oxidizes to protect itself

Aluminum oxidizes to protect itself

The reason why aluminum oxidizes to protect itself in marine applications is simple: it is very reactive to oxygen. Under water, aluminum develops a hard film of aluminum oxide, or hydrated oxide. This layer of aluminum oxidation makes it incredibly resistant to corrosion.

It also makes aluminum relatively inert chemically, which is beneficial for this material. Whenever the surface film is lost, however, the aluminum will begin to corrode and will start to look like a freezer burnt vanilla ice cream.

While aluminum oxidizes to protect itself in marine applications, it will corrode if it is exposed to water for a prolonged period. In order to protect aluminum, it must be isolated from incompatible metals, such as stainless steel.

Aim to reduce the risk of this corrosion by using bedding fasteners, which can slow the corrosion cell down. However, it is important to note that the use of sacrificial anodes is only effective in the submerged zone.

Anodizing is another common way to protect aluminum. It creates a protective oxide film, which is attractive when it comes to finishing aluminum. However, this method of oxidizing aluminum is not suitable for larger fabrications.

In these cases, many boaters use a sacrificial anode made of zinc, which corrodes more rapidly than aluminum and must be replaced periodically. This approach, however, requires immediate attention and is not suitable for larger fabrications.


When choosing a marine caulk or silicone for a project, consider its bond strength and how flexible it is. While some silicone and marine caulk products are completely flexible, others have the consistency of a paste.

While these can be applied over most surfaces, a thin layer of silicone is much more flexible than a thick coating. To determine whether a given product is suitable for your project, read this guide to marine caulk.

Silicone is a synthetic polymer that belongs to the rubber family and has long been a favorite among boat maintenance professionals. Because it is UV and heat resistant, silicone is a great gasket material. However, its weakness makes it unpractical for use below water.

In general, however, silicone is a great choice for sealing boats and yachts. It is also waterproof and weatherproof, making it the ideal marine caulk for your project.

The most common marine caulk is polyurethane. This sealant has excellent water resistance and adhesive power. It is suitable for sealing seams both above and below the waterline, but not all polyurethane products are waterproof.

Other products used by traditional wooden boat builders include Oakum, Caulking Cotton, Seam Cement, Caulking Irons, and Bedding Compounds. These products are also good for above-waterline planking applications.

Resistance to chemicals

One of the most important differences between silicone and marine caulking is resistance to chemicals. Silicone is a flexible, pliable material that is highly resistant to UV rays and salt water. It is also waterproof, making it an excellent choice for boat-building applications.

BoatLife’s Life Seal is a silicone-polyurethane blend. 3M 3000UV is a silicone-modified polyurethane (SMP) with reduced adhesion. Both silicone and marine caulks are compatible with plastics, but it is important to remember that fresh silicone cannot be painted.

A second difference between silicone and marine caulking is their ability to resist mold and mildew. Silicone is highly resistant to UV rays and most marine-grade silicone contains mildicide to help prevent mold and mildew from growing.

This silicone also tends to retain its flexibility for longer in a marine environment. When choosing between silicone and marine caulking, choose the one that best meets your needs.

In general, silicone is more resistant to water, while nitrile is better at resisting ozone and hydrocarbon fuels. However, it cannot be used in food applications due to its phthalate-based composition.

Fortunately, silicone is food-grade and is often used for food processing equipment. The biggest difference between silicone and marine caulking lies in their chemical resistance. If you’re looking for a long-term, reusable seal, silicone is the way to go.


Although some silicone and polyurethane compounds are excellent for underwater use, silicone is not an ideal material for bedding through-hull fittings or transducers. A more suitable material is polyurethane, which is more flexible and pliable.

However, silicone is not an ideal material for bedding fasteners or deck hardware because it leaves a residue on surfaces. This residue can also cause damage to painted surfaces.

A hybrid sealant made of a silicone and polyurethane is an excellent choice if durability is important. It can last 20 years or more, but will start looking like frayed chewing gum after a few years.

These two types of marine caulking are not compatible for use below the waterline, which is why manufacturers combined the properties of silicone and polyurethane to create a hybrid material that is more durable and lasts longer.

Although the hybrid product is less flexible, it can be applied to most surfaces, but it is not as strong as silicone or polyurethane.

A polyether-based marine caulk, TDS Multi-Caulk Sealant, is one such product. It is advertised as a versatile waterproof sealant for both above and below the waterline. It can be used on wood, glass, and metal.

It is also unaffected by certain oils and teak cleaners. However, you should always remember to read the product label before committing to a purchase.

Frequently Asked Questions (FAQs)

1. What is the difference between marine caulking and silicone?

Marine caulking is a type of sealant that is specifically designed for use in boats and other marine vessels. It is made from a variety of different materials, including rubber, plastic, and metal, and is used to seal up cracks and gaps in the hull of a vessel.

Silicone, on the other hand, is a type of synthetic rubber that is often used as a sealant in a variety of different applications. It is known for its high level of flexibility and resistance to heat, making it an ideal choice for use in many different types of environments.

2. When should each type of sealant be used?

When should each type of sealant be used

Marine caulking should be used in any situation where there is a need to create a waterproof seal in a boat or other marine vessel. This could include sealing up cracks and gaps in the hull, as well as around windows, doors, and other openings.

Silicone can be used in a variety of different applications, but is often chosen for its flexibility and resistance to heat. This makes it ideal for use in many different types of environments, including kitchens and bathrooms.

3. What are the benefits and drawbacks of each type of sealant?

Each type of sealant has its own set of benefits and drawbacks. Marine caulking is generally very durable and effective at creating a waterproof seal, but it can be difficult to apply and remove. Silicone, on the other hand, is much easier to apply and remove, but it is not as durable as marine caulking.

It is also important to note that silicone should not be used on surfaces that will be exposed to direct sunlight, as it can cause the surface to deteriorate.

Final Words

When it comes to marine caulking vs silicone, they both have their pros and cons, so it really depends on the specific needs of the boat owner. If price is the primary concern, then silicone may be the better option.

However, if boat owners are looking for a caulking that will last longer and provide a better seal, then marine caulking may be the better choice.

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