• Creating Patterns
• Formwork
• Pouring
• Finishing

Creating Patterns

canoe7-31.dwg

Formwork

Plywood Cross Sections: We elected to cut our cross-sections in 5/8" plywood linked by grooved 2x4's. Plywood can be bought in 4x8' sections from any of the luber yards or home construction warehouses (i.e Home Depot) in town. Expect to pay ~$12 per sheet. You can make 4 sections out of each sheet. The department does have a large truck that can be used to transport the wood. See Prof. Katapodes (ndk) for approval and Bob Spence (bspence) to drive you. With some modification the 2x4's on hand should suffice.

The plywood sheets can be quickly cut down to size (2x4' sections) using the panel saw. Again see Bob for instructions on its operation. You may need to meet with him for a lab safety session before proceeding. This will apply to any power tool operation during regular hours.

After cutting the boards, they must be marked. Use a chalk line or square to mark centerlines and refernece lines so that all of the patterns can be aligned properly. Tape the patterns right onto the board and follow the outline. Remember to label the board before removing the labeled pattern and mark the location of the gunwales. When pouring it will be easiest to pour above the finish line and then sand down to that point. Use a jig saw to cut the board. Try your best to follow the lines, but understand that the ribbing will correct many small errors and you'll pour the canoe thicker than necessary and sand down to the desired thickness. Return to artwork.

Grooved 2x4: You will need at least 5 lengths of the grooved 2x4's. Three should be placed along the bottom of the forms and the other 2 along the side of the forms. If grooved with a small tolerance, you may not need to use any glue/nails/screws to hold the mold together at this stage. To groove the boards use a circular saw set to a constant depth and make cross cuts centered on every 6" inches. It will be easy to use a chisel to remove the wood from the groove. Be sure to check the groove size at every location with some sample of the plywood you'll be using.

Form Skin: We decided to use a heavy grade roofing felt to bridge the gaps between the plywood cross sections. Other materials like linolium and cedar strips were considered but considered to be 1) too expesive or 2) too stiff. Roofing felt can be purchased cheaply (<$30) from Home Depot and provides sufficient strength while being flexible. Still, it is likely not the best solution out there.

Cut the felt into roughly 18" wide by apropriate length sections. In most areas of the canoe, you will be able to place the strips so that they bridge three of the cross sections. Adequate overlap must be included. Make sure that at all overlaps at least one strip completely bridges the gap.

Despite the smaller strips, you may still struggle with bulging and tearing at places in the canoe where the curvature changes. To solve this problem place smaller strips in the longitudinal direction to better match the curvature. The front end could be finished by extending the last strips to a point. The aft end, howerver, will require you to carve a from from styrofoam.

Once the skin has been placed, you'll need to find some way of sealing the overlaps. Rubber cement does not seem to work. Perhaps some type of silicone cauk or a thick masking tape will work better. After a good deal of trial and error, we found that waterproof flashing tape, used for for sealing roofs, works the best.

Note: An electric stapler will make the process much easier. Plan to use a lot of staples.

Pouring

Based on mix requirements and material availablity, we decided to use a Ferrocement technique for pouring the canoe. This is an accepted marine construction method. For more information about ferrocement, see Professor Naaman who wrote a book on the subject. This technique requires the placement of several alternating layers of concrete and mesh reinforcement. Expect this proccess to take some time (on the order of 8 hours).

Mixing
It may be best to have two or more people working in the mixing lab, so that you're never waiting on concrete. A few mixing notes: 1) placement is easiest with a dry paste-like concrete consistency, 2) adding water too quickly may result in liquification of the concrete, 3) place a labcoat over the mixer when mixing the dry materials to reduce dust, 4) the small mixer can only make about 10 liters at a time.

Placement
The first layer should be thicker than the rest to allow for sanding and smoothing after demolding. However, some effort should be made to resist the temptation to make the layer too thick. In 2003, this first layer used as much concrete as the next five combined. After placing concrete over the flatter areas lay down some mesh and use it to help you form up the sides. If the mesh is only strong in one direction, as in 2003, then every layer you'll need to alternate the direction in which it is oriented to ensure isotrophy. Also be sure to provide adequte overlab for continuity. It may also help to staple excess mesh to the top of the forms to keep it in place. Expect to loose several inches from the indicated top of the gunwale due to difficulties during pouring (i.e. design with a conservative freeboard).


In consequent layers minimize thickness and work quickly before the concrete drys. It's often better to work up the sides and then along the length of the canoe. Use your hands (with gloves on) to work the concrete through the mesh.

The ends will be a problem. The mesh may need to be cut and sowed (don't need to be too carefull here) back together along a seam. It the mix is expected to be reasonalby strong, it may be best just to fill the ends with unreinforced concrete. This will make finishing easier.

Finishing

Demolding
The break-away formwork should make this much easier. Many other schools that use more solid or continuous formwork often have difficulty demolding without breaking the canoe. If using the formwork described above, be sure to support areas of the canoe as the cross-sectional ribs are removed. The tar paper will tear off easily. To get a nice clean gunwale, use a masonry blade on a circular saw to cut off unwanted height. Use a chalk line to mark the appropriate level.

Finishing
First, set up cinder blocks with some type of padding (lab coats work well) to set the canoe on up-side-down. Blocks may be found by the canoe area (inside the structures lab) and outsid the mixing lab inside the fenced area. All sanding should be done outside. Rent a belt sander with a coarse belt to do the rough work. Afterward, go back over your work with hand sanding. Wrapping the sand paper around small blocks works well.

Safety
You may be questioned about the safety of the work you're doing. Make sure dust is not blowing into any public entryway. Wear a mask and safety goggoles. If you do talk to a safety manager, they will recommend a full face shield and respirator. To avoid this problem, wet down the canoe before sanding to keep the particles down. If this is done, then you'll definitely need the coarse paper. When you are done, wash (Do NOT sweep) the dust into the grass. OESA will tell you than concrete cannot be washed down the storm drain.

Patching
Try to use a similar mix to what was originally poured. Even still, you may end up with different colors. Be carefull when sanding away extra patching that you don't sand it all away. This is primarily an asthetic step.

Waterproofing & Painting
consult the rules to see what types of waterproofing and painting is permitted. Just be sure to put down some plastic if painting inside the structures lab.