Bonding Below the Water Line; Choosing the right adhesive for bonding in Marine environments
Below the waterline is one of the most unforgiving environments, so making the right choice of adhesive or sealant is vital, whether that’s in vessel construction or emergency repairs. Bonds subjected to marine environments face constant water immersion, dynamic loads, and temperature cycling, all of which can weaken vital bonds and seals.
Challenges of the Marine Industry
A lot of the stressors of the marine industry don’t exist in other industries, requiring specialised solutions. Other than the issue of bonding underwater some of the biggest maritime challenges are:
- Water immersion - freshwater is demanding, saltwater is highly corrosive.
- Moisture ingress - a failure which may not be visible until significant damage has already occurred.
- Hydrostatic pressure - the deeper a component sits the greater the pressure, especially important in submarines and below waterline hull fittings.
- Thermal expansion & contraction - occurring with changes in water temperature causing cyclic stress.
- Structural movement & Vibration - hulls flex and propulsion systems generate vibration.
- Cleaning & chemical exposure - fuels, oils, and cleaning agents can degrade adhesive bonds.
Is bonding underwater possible?
The ability to bond and seal in submerged conditions remains extremely sought after in marine maintenance and repair. Typically, underwater repair meant dry docking the vessel, costing time and money. However, advancements in technology have changed this with certain formulations allowing for emergency hull sealing without dry docking and other applications such as sensor and transducer installation/replacement while remaining in service. However, underwater bonding still has its limitations.
Below waterline bonding and sealing applications
Below waterline bonding applications include those fully submerged and ones within the splash zones, some common applications include:
- Hull fittings i.e. depth sensors
- Keel attachment, bonding between keel and hull
- Rudder assembly
- Underwater patching and repair, important in naval and emergency vessels
- Composite and GRP laminate bonding
- Deck hardware and fittings in the splash zone
- Marine fendering and rubber to hull bonding
- Interior and exterior below waterline pipework
- Hatch sealing
- Window and glass bonding in splash zones
Requirements of marine adhesives and sealants
Many water resistance adhesives cannot be applied underwater as they will not cure in those conditions, however once cured they act as an impenetrable barrier for moisture, making them ideal options during construction. Other adhesives can be applied underwater and will cure with moisture making them ideal for quick repairs.
Some properties to consider in adhesives and sealants intended for marine environments include:
- Flexibility - rigid adhesives can crack or loose adhesion when subjected to cyclic stress
- Moisture, saltwater and/or freshwater resistance
- Watertight sealing
- Vibration and impact resistance
- Chemical resistance
- Moisture cure for underwater repairs
- Long term, durable adhesion
- Corrosion protection
Marine suitable products to consider:
Eurobond Solo – A moisture cure MS polymer which creates bonds resistant to water, sea water and aggressive environments, making it suitable for sealing applications underwater.
3M 5200 Marine Sealant/Adhesive - A polyurethane sealant which retains strength below the waterline and remains flexible, allowing for structural movement. 5200 also resists weathering and salt water.
3M 4000 UV - a one-part adhesive sealant which cures to a rubbery waterproof seal. Designed for marine including bedding and sealing applications to fiberglass hull, wood to fiberglass, porthole frames, deck fittings, mouldings, through hull and deck hardware.
3M 4200 Fast Cure Marine Sealant – an all-purpose polyurethane that reacts with moisture for a flexible bond, offers less strength than 3M 5200.
Permabond 712 – A unique cyanoacrylate which offers outstanding underwater resistance, and can adhere to metals, plastics, and rubbers, making it ideal for pipe seals and gaskets.
Whether it’s vessel construction, maintenance or temporary repairs, understanding the technology behind the bond is the first step to specifying adhesives with confidence. Speak to our marine expert for a complimentary consultation regarding your marine bonding application.
