Sika Sikaflex-291 LOT Long Open Time Marine Adhesive Sealant – 300ml Cartridge

Long Open Time Marine Sealant Sikaflex 291 LOT is a long open time marine sealant from Sika. It is a non-sag, 1-component, moisture-curing polyurethane built for jobs that need extra working time, such as bedding-in teak plank decking laid on the sub deck. It makes elastic, vibration-resistant joint seals and bonds to wood, metals, metal primers, 2-component paint coatings, and fiberglass. The window before it skins over is longer than standard Sikaflex 291, so large joints and long rails can be set and aligned without rushing. Supplied in white, black, or mahogany in a 300 ml cartridge, made in the USA. It cures from moisture in the air, so there is nothing to mix. Sika positions it against 3M® 4200™ for marine sealing where extra working time is needed. The comparison is covered below.

Key Product Details

(A) 23 °C (73 °F) / 50 % r.h. (B) Stored below 25 °C (77 °F). Typical values from the Sika product data sheet, version 03.01 (04-2023).

Suitable for experienced professional users only. Tests with actual substrates and conditions are needed to confirm adhesion and material compatibility.

Performance in Production

• A 4 hour skin time at 23 °C and 50 % relative humidity gives the working window for large joints, long rails, and decking where alignment takes time. Standard Sikaflex 291 has a 60 minute skin time.
• Tooling and finishing have to be done inside the skin time, so the longer window covers tooling as well as setting parts.
• A Good non-sag rating means the bead holds its shape on vertical joints instead of slumping.
• Shore A 45 with 550 % elongation at break gives an elastic cured seal for vibration-resistant joints.
• It processes from 5 to 40 °C (41 to 104 °F), with 15 to 25 °C (59 to 77 °F) as the optimum for substrate and product. One component means no mixing, and it runs through manual, pneumatic, or electric piston guns.
• The cured sealant can be sanded and painted after a skin forms. 1C-PUR and 2C-acrylic paints are usually suitable. All paints have to be tested under production conditions, and baking paints call for a full cure first.

Common Applications

• Bedding-in teak plank decking laid on top of the sub deck
• Large joints and long rails that need extra working time, such as rub rails
• Elastic, vibration-resistant joint seals in marine construction
• Interior sealing applications in marine construction
• Sealing to wood, metals, metal primers, 2-component paint coatings, and fiberglass
• Marine sealing above and below the waterline
• Wood-boat work where a mahogany-colored sealant is wanted

Available Sizes and Colors

Sikaflex 291 LOT as an Alternative to 3M 4200

Sika positions Sikaflex 291 LOT against 3M 4200 for marine sealing where extra working time is needed, such as large rub rails and teak decking. Check your joint against the TDS values above and test on your own substrates.

Related Products

• Sika Sikaflex-291 Marine Adhesive Sealant – 300ml Cartridge: Sika’s general-purpose marine sealant, with a 60 minute skin time
• Sika Sikaflex-292 Marine Adhesive Sealant – White – 300ml Cartridge: Sika’s structural bonding adhesive for joints under high dynamic stress

How to Apply Sikaflex 291 LOT for Deck Bedding and Large Joints

These steps follow the Sika TDS. Run them on a test joint with your own substrates before production.

1. Prep the surfaces. They must be clean, dry, and free of grease, oil, dust, and contaminants. Pre-treatment depends on the substrate, so check Sika’s Pre-Treatment Chart for 1-component polyurethanes and verify on your original substrates.
2. Apply the sealant. Process between 5 and 40 °C (41 to 104 °F), with 15 to 25 °C (59 to 77 °F) as the optimum for substrate and product. Use a manual, pneumatic, or electric piston gun.
3. Set parts and tool inside the skin time. Tooling and finishing must be done inside the skin time. Sika recommends Sika® Slick as the finishing agent. Test any other finishing agent for compatibility first.
4. Let it cure. Cure comes from atmospheric moisture. It runs slower at low temperatures because the air holds less water.
5. Paint after a skin forms. 1C-PUR and 2C-acrylic paints are usually suitable. If the paint needs a baking process, let the sealant fully cure first. Test all paints under your manufacturing conditions.
6. Clean up. Uncured sealant comes off tools and equipment with Sika® Remover-208 or another suitable solvent. Cured material can only be removed mechanically. Wash hands and exposed skin right away with an industrial hand cleaner and water, and keep solvents off skin.

Substrates covered by the TDS: wood, metals, metal primers and 2-component paint coatings, and fiberglass. Do not use it to seal plastics prone to stress cracking, such as Plexiglass and polycarbonate.

Frequently Asked Questions

What is Sikaflex 291 LOT used for?

Sikaflex 291 LOT (also called Sika 291 LOT and Sikaflex-291 LOT) is the long open time version of Sika’s 1-component polyurethane marine sealant. The TDS names bedding-in of teak plank decking laid on the sub deck as a main use, along with elastic, vibration-resistant joint seals and interior sealing. It bonds to wood, metals, metal primers, 2-component paint coatings, and fiberglass. This listing is the 300 ml cartridge in white, black, or mahogany, made in the USA.

Is Sikaflex 291 LOT an alternative to 3M 4200?

Yes. Sika positions Sikaflex 291 LOT against 3M 4200 for marine sealing where extra working time is needed. Check your joint against the TDS values above and test on your own substrates. Call us if a customer spec names 4200 and you want to talk through the swap.

What is the difference between Sikaflex 291 and Sikaflex 291 LOT?

LOT stands for long open time. Per the TDS, standard Sikaflex 291 has a 60 minute skin time and 291 LOT has a 4 hour skin time. LOT also comes in mahogany, and standard 291 comes in white and black. The cured seals are close in hardness, Shore A 40 for 291 and Shore A 45 for LOT.

What is the working time on Sikaflex 291 LOT?

At 23 °C and 50 % relative humidity the TDS gives a skin time of 4 hours. The TDS does not list a separate open time for LOT, so treat the skin time as the limit for tooling and finishing, and test your joint for set time. Temperature and humidity change the real window. The TDS cure diagram plots cured thickness against days at 23 °C and 10 °C.

Can Sikaflex 291 LOT be used below the waterline?

Yes. The TDS lists use above and below the water line, and resistance to fresh water and seawater. Surface prep still depends on the substrate and has to be verified by testing, so call us with your joint if you have questions.

Is Sikaflex 291 LOT UV resistant?

No. Sikaflex 291 LOT does not have UV stability. The TDS does not list UV resistance, and Sika recommends a UV-stable sealant such as Sikaflex-295 UV for joints that stay exposed to sun. Call us and we will match the product to the joint.

Can you paint over Sikaflex 291 LOT?

Yes. Per the TDS, Sikaflex 291 LOT can be painted after a skin forms and can be sanded. 1C-PUR and 2C-acrylic paints are usually suitable. If the paint needs a baking process, let the sealant fully cure first. Paint is usually less elastic than the sealant and can crack in the joint area, so test every paint under your production conditions.

Can Sikaflex 291 LOT be used on acrylic or polycarbonate windows?

No. The TDS says Sikaflex 291 LOT must not be used to seal plastics prone to stress cracking, such as Plexiglass and polycarbonate. Sika’s marine team points to Sikaflex-295 UV for acrylic and polycarbonate windows. Call us before you pick a sealant for window work.

Questions on fit for your marine sealing application? Call (800) 220-1966 or email [email protected].

3M and 4200 are trademarks of 3M Company. Sikaflex is a registered trademark of Sika Corporation. Chemical Concepts is not affiliated with 3M. Product names are used for reference only.