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What Is the Difference Between Polysulfide and Polyurethane Sealant? 

 December 18, 2020

By  Dale Keese

Boats will require maintenance and repairs as they age, which is why you need to know about the right marine sealants to use. For instance, polysulfide and polyurethane marine sealants possess different qualities that make them useful in distinct ways.

Polysulfide sealants are mainly used on areas that will be submerged for prolonged periods of time. Meanwhile, polyurethane sealants excel when they’re used to cover the hull-to-deck joint. There are also notable differences between the two in terms of adhesive strength, curing time, and several other factors.

Choosing correctly between polysulfide and polyurethane sealants is crucial if you want to properly maintain or repair your boat. Read on to learn exactly which marine sealant will work best for the boat problem you’re currently facing.

Wear and tear is a problem for boats of all sizes. Since boats are routinely exposed to moisture and other elements that can speed up deterioration, the effects of wear and tear may show up on them sooner. Given that small issues affecting your boat’s body can grow quickly, addressing them promptly is a must.

That’s where marine sealants come in. Marine sealants will help boat owners plug the annoying leaks that pop up from time to time. Depending on the kind of sealant they use, they may also be able to strengthen the structural integrity of their boat.

Among the options you have when choosing a sealant to use on your boat are the polysulfide and polyurethane sealants. While they are both capable of plugging a leak, how effectively they do that can vary depending on certain factors.

Let’s start with the polysulfide sealants. The polysulfide sealants can be used on different spots of your boat. Still, they’re most useful on areas that will be submerged in the water for extended periods of time.

The reason why they excel in that role is because of how effectively they can waterproof the spots they cover.  Polysulfide sealants can effectively eliminate any risk of continued leakage. They even do a good job of protecting against erosion, thus allowing the seal to stay in place longer.

Also contributing to the remarkable longevity of polysulfide sealants is their ability to withstand different chemicals. That’s an important thing to note because many bodies of water are unfortunately contaminated to some degree. The new sealant you used should be able to stand up well to those pollutants.

Some boat owners also prefer using polysulfide sealants because they can be sanded down. Paint over the polysulfide seal after it dries and create a smooth finish.

Polyurethane marine sealants will also cover up any holes that show up on your boat. They are at their best when used to seal up the hull-to-deck joint. You can count on polyurethane sealants working well on the rail portions of your boat.

If you take the time to seek them out, you can find polyurethane sealants that withstand UV exposure really well. Feel free to use those polyurethane sealants on parts of your boat that will be exposed to the sun. The seal will not fail even if those parts are continually exposed for long periods of time.

Again, it’s important to note that not all polyurethane marine sealants possess that quality. You have to look for the ones that are specially formulated to offer that kind of protection.

Another thing to note about polyurethane marine sealants is that it has strong adhesive properties. The bond it forms between two surfaces can be very tight. That can be a double-edged sword of sorts so be careful when using this marine sealant in that capacity.

Compared to the polysulfide options, polyurethane sealants also cure faster. Go with the polyurethane sealant if you’re planning to use your boat soon after making repairs.

Cost is always an important factor to consider when choosing between products in the same category. In this case, you may find polyurethane sealants to be the more affordable option. There are polysulfide sealants that are priced similarly to their polyurethane counterparts, but they are harder to find.

How Are Polysulfide and Polyurethane Marine Sealants Similar?

There are numerous dissimilarities between polysulfide and polyurethane marine sealants. However, the two products also share some similarities. Perhaps the most notable point of similarity between the two is how they react to a certain kind of surface.

While polysulfide and polyurethane sealants can be effective on numerous material surfaces, they still aren’t suitable for all of them. To be more specific, you should probably look for an alternative if you want to seal plastic surfaces.

Those two sealants have an odd kind of effect on plastic. After being applied, the solvents present in the polysulfide and polyurethane sealants may have an adverse reaction to the plastic surface.

The solvents may cause the plastic surface to harden significantly. As the solvents continue to attack the plastic, the surface may harden excessively until it eventually splinters. Avoid using polysulfide and polyurethane sealants on the plastic parts of your boat unless you want to have a serious problem.

Also, both polysulfide and polyurethane marine sealants are pretty easy to apply. You should be able to use either one with no problem as long as you have the right tools on hand.

Is It Easier To Find Polysulfide or Polyurethane Sealant?

The marine sealant market has changed quite a bit in recent years. While you could find both polysulfide and polyurethane sealants with no issue before, that may no longer to be the case. To be more specific, it seems that more manufacturers are discontinuing production of their polysulfide sealants.

It’s unclear exactly why polysulfide sealants are becoming less common. However, it could have something to do with their chemical composition.

In some cases, boat owners may not have a choice between getting a polysulfide or polyurethane sealant. There’s a chance that only the polyurethane sealants are available in their area.

Frequently Asked Questions

What Are the Different Types of Polyurethane Sealants?

While shopping for a polyurethane marine sealant, you’ll find that there’s more than one kind available. You may find a standard variant, as well as other items labeled “medium-strength” and “high-strength.” So, what do those other labels mean?

When it comes to polyurethane sealants, the strength labels refer to the adhesive capabilities of the product. Even the standard variant of a polyurethane sealant already offers a lot of adhesive strength. The additional variants can form significantly tighter bonds after application.

How Do You Apply Polysulfide and Polyurethane Marine Sealants?

Polysulfide and polyurethane sealants can be applied in similar ways. First off, you can apply either one using a caulking gun.

Place the tube of whichever marine sealant you chose into the caulking gun and secure it. Once in place, cut the tip open to allow for the passage of the sealant. Proceed to apply carefully and try to keep the amount even as you move across the target surface.

Both marine sealants can also be applied without the use of a caulking gun. Snip the tip of the tube open and then carefully push out the sealant. Just like with a caulking gun, work carefully to ensure that the sealant is evenly applied over the surface.

What Are the Other Types of Marine Sealants?

Aside from the polysulfide and polyurethane options, there are other types of marine sealants currently available. Silicone sealants are probably the most common.

Silicone sealants provide a good seal and decent protection against UV rays and chemicals. However, they cannot last long against water and they also affect the paint you use. Because of those drawbacks, silicone sealants only have limited uses on boats.

You can also find silicone and polyurethane hybrids. Unlike pure polyurethane sealants, you can use the hybrid options on plastic surfaces with no issue. They silicone and polyurethane hybrids don’t offer much in terms of adhesion though.

Boat owners can also turn to butyl tape if they need to cover a leak. Butyl tape is the easiest marine sealant to use, but it also offers nothing in terms of adhesion.

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