August 4, 2003 : Applying the Fillets to the Bulkheads/Joints -
Shown above is the basic "starter kit" for filleting the bulkheads. Starting on the far right are two large cans of Super Bond Epoxy, a 2-part glue. Moving to the left on the back row is Colloidal Silica, a thickening agent. On top of the silica is a 5-quart disposable mixing bucket. Further to the left is a 2-part epoxy laminating resin. Other items in the picture include paper towels, rubber gloves, a plastic stirring stick, white vinegar (for cleaning resin off hands, tools, etc.), wooden stirring sticks, and some spreaders. Not shown are paper sleeves, a respirator, eye protection, and a throw-away brush.
The first step is to cut the spreader to the appropriate shape to fill the joint between the bulkhead and the hull. The thickness of the fillet should be approximately the same as the thickness of the bulkhead - 3/4 of an inch. To get the right shape for the spreader I hold up different size cans against the joint until I find a can/container that is the right shape. I use this container to mark a radius on the spreader and then cut the shape out of the spreader with some tin snips.
The next step is to mix up a small batch of laminating resin and apply a coat to the joint that will get the fillet. The purpose of applying a coat of laminating resin is that the hull will try to leach the resin out of the glue, leaving a dry (and possibly weak) joint. I usually mix-up and apply the laminating resin 15-20 minutes before applying the fillet. (I want the resin to get sticky so the fillet won't slide.) On my first joint I try to pick the back of a bulkhead that can't be seen from the outside/cockpit of the boat. This is my "practice" application.
Next I mix the two-part glue. Once the glue is mixed and has been stirred for several minutes, I add the thickening agent. The temptation here is to make the agent too thin, which can be a costly mistake. (If the glue goes on too thin it will sag and run down the bulkhead, making it necessary to grind the glue off and reapply the fillet.) Once the glue has been thickened it can be applied to the joint with a stirring stick or spatula. After the glue is in place, the final step is to use the pre-cut spreader to smooth the joint. I suggest making only one or two passes and calling it quits. The reason for this is that if the glue starts to "cook off" while you are making the fillet, multiple passes will cause the glue to "pull" and get out of shape.
A note on safety - wear gloves and eye gear. If you don't have good ventilation, wear a respirator. If (when) you get epoxy on you, use white vinegar to remove it as soon as possible. Since these photos were taken I have bought paper sleeves and pants and will wear them in future sessions.
|Using the disposable brush to pre-coat the joint.||Mixing the thickener with the glue. This batch has reached the consistency of dough and is ready to apply.|
|Applying the glue to the joint.||Using the spreader to make a fillet.|
This is how the final fillet should look.
After the fillet is finished it's important to take a flat spreader and clean up all of the drips and extra globs that have fallen on either side of the fillet. This will eliminate a lot of sanding and grief after the resin has set.
Now you have some choices to make. This is a good time to re-wet the joint with laminating resin and apply the fiberglass tape to finish the joint. In order to do this it is necessary to pre-measure and precut the tape/cloth and have it ready to apply. In a production shop this is usually a two man job, with the man outside the boat wetting out the cloth and handing it to the inside man. My personal preference is to let the resin harden and hit it with a 36 grit disc on a grinder before applying the tape to the joint. This requires some extra work but allows me to control the process a little better and break the work units down into smaller increments.
Roger and I survey the progress!
During this session Roger acted as the "outside man", handing glue, tools and paper towels in and out of the boat as needed. He was instrumental in keeping things orderly and clean. He also watched the work and pointed out areas that needed attention to detail. Many thanks to him for his help!
Several days ago I received and email from James G. Jones. James is also building a Dipper and has a web site that can be seen at: http://home.comcast.net/~jgj252/BB/Dipper.htm . I've taken a look at his site and am very impressed! James's boat will be a little different from mine in that he's building a full cabin version whereas my boat will have an open cockpit. It's obvious that he's doing and excellent job and I recommend visiting his site.