How to bond bulkheads and panels into a boat hull.

A fillet is a cove shaped application of thickened epoxy that bridges a inside corner joint such as a bulkhead to hull joint. It is excellent as it increases the area of bond and also serves as a structural brace. Any joints specified in plans to be covered with fibreglass cloth will require this.
Difficulty: Moderately Easy
Remove any flaky, blistering, chalking or old coatings from the surfaces to be joined by scraping etc.
Sand marine hardwoods and non-porous surfaces using 80 grit aluinium sandpaper to obtain a abraded surface, which will provide a good texture for the epoxy to key into.
If the surface is a cured epoxy surface, it will likely have an wax like film which is a bi-product of the curing process. This will need to be removed by simply washing down with clean water and scrubing with a 3-M scotch-brite pad, before the surface drys wipe the disolved waxes off with clean paper towells. After the washing the surface should appear dull. sand paper will just clog.
Before bonding the 2 joints, check both parts for proper fit and surface preparation, and over any areas that need protection from accidental spills.
Remove sanding dust.
Using the West System Mini pumps, dispense 3 full pumps each of West System resin 105 and west System hardener 205 into a mixing container.
The container should be a clean plastic, metal or wax-free paper container, glass or foam containers are not suitable because of the exothermic heat build up from the reaction produced when the 2 ingredients are mixed together.
Using a flat wooden stick mix the resin for 1 to 2 minutes ensuring to scrape the sides and bottom of the container as you mix. Use the flat end of the stick to reach the corners of the container.
Caution: Heat is generated by the chemical reation that cures the epoxy. I have had a plastic container melt as a result of mixing more than I could apply before the end of the epoxy pot life. If this begins to happen take the container out side to cool off safely and dispose of it only when it is cold.
Apply a coat of thoroughly mixed resin to the 2 surfaces to be bonded with a brush or small foam roller for larger areas.
This method is the best of 2 methods as it promotes maximum epoxy penetration into the bonding surface preventing resin starved joints.
Modify the resin hardener mixture by stirring in the appropriate filler 403, 405 or 406 until it becomes thick enough to bridge any gaps between the joints preventing "resin starved" joints.A mayonnaise to peanut butter consistancy will work fine. Allow for a shorter working life of the mixture.
Apply enough of the resin filler mixture to one edge, so that a small amount will squeeze out as the surfaces are joined together with force similar to a hand grip.
Once the joints are properly aligned, attach the clamps to hold the parts in position, then use just enough pressure to squeeze a small amount of epoxy mixture from the joint, indicating that the epoxy is making good contact with both surfaces and filling all or any voids etc.
Avoid using too much pressure resulting in squeezing all of the mixture out of the joint.
Make sure that plastic or peel ply (release fabric) is used under clamps to prevent them becoming bonded to the surfaces.
Using a fillet tool crafted out of a piece of thin plywood, veneer or sheet metal with a suitable radius for example 40mm radius, shape or remove any excess mixture that squeezed from the joint. Add more mixture to the fillet tool if necessary to produce a perfectly radiused fillet joining the 2 parts together.
If the plans specify fibreglass tape as structural reinforcing then simply apply pre-wetted out fibreglass tape to the joint and gently roll into place with a small foam roller.
Apply some peel ply (release fabric) over the finished fillet joint, smoothing out gently with gloves until the resin is bought to the surface of the release fabric wetting it out, and leave the joint to cureto cure.
Items needed
  • Gougen Brothers West System Resin 105
  • Gougen Brothers West System Hardener 205
  • Gougen Brothers West System calibrated Mini pumps
  • Gloves
  • Protective clothing
  • Mixing containers
  • Flat mixing sticks
  • Masking tape
  • Peel ply (release fabric)
  • Glass fibre tape
  • Clamps
  • Acetone cleaner or lacquer thinners.
  • Paper towells
  • Radiused Fillet tool made from veneer, marineplastic or sheet metal
Overall tips
  • Practice makes perfect as they say, and unfortunately unless you are gifted then the first fillets will require a couple of attempts. Let the first attemp cure with any inperfections, then apply more mixture later, and this time those "dragged" holes etc will be filled.
Overall warnings
  • --Epoxy reins is relatively safe however follow the instructions on the containers and there will be no problems. Use gloves and other protective clothing, and for no other reason this adhesive is so good it will destroy those good clothes and probably your relationship with your wife. After 2-3/4 years of continous use I suffered no problems.