Adhesives

Last week we had a short class on adhesives given by Bruce, who heads the contemporary boat building program at the school. Besides being an excellent wood boat builder and instructor, Bruce is an expert on everything sticky...what I meant to say is specifically adhesives, glues and especially epoxy. No judgement will be made in comparing "traditional" boat building techniques to the newer ones that use plywood, laminates and composite materials. In a very short boat building career (two weeks) I have found that adhesives do play an important role in all types of boat building.

How do you know? The answer is you just do. Actually, Bruce explained the numerous tests that he has tried using various adhesives and how they performed as advertised. One caveat is that you MUST always follow the manufacturer's recommended instructions. Period.

What do you need to do to use adhesives effectively:
1. good glue joint
2. correct clamping pressure
3. no gap filling

Some of the products used:

J-B WoodWeld is a fast setting two-part epoxy system formulated for wood bonding and repairs. When fully cured it can be shaped, tapped, filed, sanded and drilled. It provides a lasting permanent bond that is stronger than the wood! J-B WoodWeld has a 1:1 mixing ratio, sets in 6 minutes and cures in 1-3 hours. Rated at a tensile strength of 1800 PSI, J-B WoodWeld cures to a light tan color.

Titebond III Ultimate Wood Glue is the first one-part, water cleanup wood glue ever offered that is proven waterproof. The waterproof formula passes the ANSI/HPVA Type I water-resistance specification and offers superior bond strength, longer open assembly time and lower application temperature. 

Titebond III is non-toxic, solvent free and cleans up with water - safer to use than traditional waterproof wood glues. It provides strong initial tack, sands easily without softening and is FDA approved for indirect food contact (cutting boards). The ultimate in wood glues - ideal for both interior and exterior applications.

3M™ Marine Adhesive Sealant 5200 is extremely strong and retains its strength above or below water line. Stays flexible too - allows for structural movement. Has excellent resistance to weathering and salt water.

• High performance polyurethane adhesive/sealant becomes tack-free in 48 hours, fast cure product in 1 hour
• Strong seal retains strength above or below the water line
• Excellent resistance to weathering and saltwater

SIKAFLEX®-291

Sikaflex-291 is a 1-component, marine grade polyurethane elastomeric adhesive and sealant. Used by many boat builders, its fast cure time makes it ideal for applications where speed is important.

General all-purpose marine sealant, which may be used for light duty bonding.

• Use above and below water line
• Resists salt water
• Fast strength build-up
• Excellent adhesion to gelcoat, fiberglass, metal and wood
• May be squeezed or brushed into place
• Stable
• Paintable
• Versatile packaging
• Excellent bond
• Fast tack-free time
• High solids content
• Sandable

** One tip when using a compound to form a gasket (for say a thru hull) is to snug the fastener but not tighten, wait 24 hour for the compound to cure and then tighten the fastener.

EPOXY

Used for bonding, coating, laminating and glass work.
Best used with a metering pump as the mixture needs to be accurate.
West Systems - 105 Resin ans 206 Hardener mixed at a 5 to 1 ratio.

Bruce's Rules for Mixing Epoxy:
1. flat bottom cup
2. non-waxed cup
3. sides must form a right angle
4. use a mixing stick
5. use gloves
6. mix for 60 seconds

Specialty Epoxies:

WEST SYSTEM 650-8 G/flex Epoxy
A toughened, versatile, liquid epoxy for permanent waterproof bonding of fiberglass, ceramics, metals, plastics, damp and difficult-to-bond woods. With a modulus of elasticity of 150,000 PSI, it is a bit more flexible than standard epoxies and polyester, but much stiffer than adhesive sealants. This gives G/flex 650 the ability to make structural bonds that can absorb the stress of expansion, contraction, shock and vibration. It is ideal for bonding dissimilar materials. It can be modified with West System fillers and additives, and used to wet-out fiberglass tapes and fabrics. Mixed at a 1:1 ratio, G/flex 650 gives you 45 minutes of working time at room temperature. It reaches an initial cure in 7 to 10 hrs and full cure in 24 hrs.

LOCTITE® EPOXY INSTANT MIX™ 5 MINUTE
Loctite® Epoxy Instant Mix™ 5 Minute is a two-part adhesive consisting of an epoxy resin and a hardener. When mixed in equal volumes, the resin and hardener react to produce a tough, rigid, high strength bond, which starts to set in 5 minutes and reaches handling strength in 1 hour. The static mix nozzle delivers a uniform mixture of resin and hardener every time. It can be used as an adhesive for a wide range of materials or as a versatile filler for gap bonding, surface repairs and laminating. Loctite® Epoxy Instant Mix™ 5 Minute does not shrink and is resistant to water and most common solvents. It can be tinted with earth pigments, cement or sand for color matching and can be sanded and drilled.
** Tip for using rags. Fold it multiple times. Wipe in a straight line. Only use side once, Fold over to use remaining clean sides.