SMP vs. Polyurethane Marine Sealant: How to Choose

Bostik 940A and 940A FS are SMP marine adhesive sealants in Iris's range. Bostik 920 and 920 FS are polyurethane (urethane) marine adhesive sealants. Those family labels help organize the available choices, but they are not compatibility lists or a guarantee that each product fits the same materials and conditions.

Start by identifying the actual product as well as its chemistry. A family comparison cannot replace the current product documentation. Avoid transferring a characteristic from one formulation to every SMP or polyurethane product, or assuming that products with similar marine descriptions are interchangeable.

Describe the function before comparing products. Bonding joins components; sealing closes a joint. An assembly may involve both, but the required behavior, joint design and installation sequence still need to be identified. A broad request for marine adhesive sealant leaves those questions open.

For sealing, describe how the joint moves in service and the size and design of the joint. For bonding, describe what is being joined and how the parts will be positioned during assembly. These are application details for Iris to review, not a basis for assuming that one chemistry is stronger or better for every marine job.

Identify the material on both sides, including any paint, coating or other surface finish. Fiberglass or aluminum is a starting description, not a complete preparation instruction. The surface that the product actually touches and the service conditions determine which documentation and preparation guidance need to be checked.

Unidentified materials and low-surface-energy plastics are review cases in the existing Iris application guidance. Do not treat the SMP or polyurethane label as proof of adhesion to a plastic, coating or mixed-material assembly. If the material or preparation cannot be verified, send the details through Application Support rather than selecting a family by reputation.

Tell Iris whether the joint sees weather, sun, spray, salt, washdown or below-waterline service. These conditions belong in the application review. A marine label alone does not establish suitability for every exposure, and a product used in one joint is not automatically the answer for a different interface on the same boat.

Glass bonding with UV exposure is a separate system question. Bostik states that 920 FS is not designed as a glazing sealant where the adhesive bond to glass is exposed to sunlight and UV. That does not mean every SMP product is an approved glazing adhesive. For a window, confirm the glazing material, frame, joint and bond-line protection through the relevant window application guidance.

Bostik describes 940A FS as a fast-set, fast-skinning version of its SMP marine adhesive sealant; 940A is the standard version. Bostik likewise offers 920 FS as a fast-curing version of the standard 920 urethane. Consider how long the crew needs to position, assemble and tool the joint before deciding whether faster progress is useful.

Fast Set is not automatically better. A larger, detailed or multi-step installation may need more working time, while another job may benefit from an earlier handling profile. Describe the work sequence and installation conditions to Iris; do not choose by the FS suffix alone or assume the same timing across chemistry families.

Request current Bostik technical documentation through the existing product-page forms for working, handling and cure information. This comparison gives no universal time figure. The exact product and application conditions must be considered before a schedule is treated as appropriate for the installation.

Preparation is also product- and substrate-specific. This guide does not assign a primer or surface-preparation product by chemistry family. Send Iris the substrates, coatings, exposure, movement, installation sequence, handling needs and desired color. Where those details remain uncertain, Application Support is the next step, not a blanket conclusion that SMP is always better than polyurethane.