Whether you're installing new deck hardware, resealing hatches, or completing a full boat restoration, choosing the right marine sealant can make all the difference. Two of the most popular options are Sikaflex 291 Fast Cure and Sikaflex 291 LOT (Long Open Time).

While both are premium polyurethane marine adhesive sealants designed for above and below waterline applications, each is better suited to different types of projects.

This guide explains the differences so you can confidently choose the right product for your next marine repair or installation.

What is Sikaflex 291?

Sikaflex 291 is a one-component, moisture-curing polyurethane adhesive and sealant trusted by boat builders and marine professionals around the world.

It provides:

• Strong adhesion to common marine materials

• Permanent flexibility after curing

• Waterproof sealing

• Excellent resistance to vibration, weather, and saltwater

• Paintable and sandable finish after curing

Common applications include:

• Installing cleats

• Bedding deck hardware

• Sealing hatches and portlights

• Rub rails

• Hull fittings

• Cockpit accessories

• Marine windows

• General waterproof sealing

Both Sikaflex 291 Fast Cure and Sikaflex 291 LOT offer these same core benefits.

Sikaflex 291 Fast Cure

As the name suggests, Sikaflex 291 Fast Cure is designed for projects where quicker curing is important.

Because it begins curing sooner, it's ideal when:

• You're making smaller repairs

• You want the boat back in service quickly

• Parts are already positioned and ready for installation

• Downtime needs to be minimized

Best Uses

• Replacing hardware

• Quick maintenance jobs

• Small sealing projects

• Emergency repairs

• Routine boat maintenance

Sikaflex 291 LOT (Long Open Time)

Sikaflex 291 LOT provides a longer working time before the sealant begins to skin over.

This extra installation time makes positioning hardware easier during larger or more complicated jobs.

It's especially helpful when:

• Installing multiple fittings

• Working in warm temperatures

• Bedding long rails

• Aligning larger components

• Completing projects where precision matters

Best Uses

• Large deck hardware installations

• Window installations

• Hatch replacements

• Rub rail installation

• Multi-piece assemblies

• Professional boat builds

Fast Cure vs Long Open Time

Which One Should You Buy?

Choose Sikaflex 291 Fast Cure if:

• You want a faster curing product.

• You're replacing hardware or making smaller repairs.

• You want to reduce downtime.

Choose Sikaflex 291 LOT if:

• Your project requires extra installation time.

• You're installing larger components.

• You want more time to position parts before the sealant begins curing.

Can They Be Used Below the Waterline?

Yes.

Both Sikaflex 291 Fast Cure and Sikaflex 291 LOT are suitable for sealing applications above and below the waterline, making them excellent choices for a wide variety of marine maintenance and repair projects.

Always follow Sika's surface preparation and curing recommendations for the best results.

Available Colours

Both products are available in:

• White

• Black

Choosing the right colour helps create a cleaner finished appearance by matching your boat's gelcoat or hardware.

Final Thoughts

Both Sikaflex 291 Fast Cure and Sikaflex 291 LOT are trusted marine adhesive sealants designed to provide long-lasting waterproof performance.

The decision comes down to one simple question:

Do you need more working time, or do you need the job finished sooner?

If speed is your priority, choose Sikaflex 291 Fast Cure.

If installation time is more important, Sikaflex 291 LOT gives you the extra flexibility needed for larger or more detailed projects.

No matter which version you choose, you'll get a professional-grade marine sealant built to handle the demanding conditions found on boats, RVs, trailers, and other outdoor applications.