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13. Trimming, sanding fiberglass and splitting the kayak shell form the mold

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In order to achieve a smooth surface for varnish, I recommend 3 to 4 additional filler coats to completely bury the weave of the fiberglass.
(this may depend on the type of Epoxy you choose)
My preference for mirror like surfaces with the least amount of sanding requires one round of intermittent sanding prior to the last two epoxy coats.
The deck in the photo may look like it has been varnished but only one session with coarse sandpaper was necessary to achieve this.
These 'doodles' are neither from boredom nor from frustration over bad epoxy job. After the last filler coat of epoxy, I draw a dense grid by magic marker to color both the high as well as the low spots on the surface. This technique saves a huge amount of time during sanding and virtually guarantees that your kayak will be perfectly prepared for varnish.
How, Why? When the surface is coated with water as you wet sand, it is almost impossible to see the dimples and imperfections and how much material you are actually removing (also true for varnishing). When you are done sanding and the hull dries, you will suddenly see hundreds of small, shiny low spots that your sander missed. The magic marker in the low spots will tell you to keep sanding and when it is OK to move on (you don't have to stop hundred times to check on your progress).
The disadvantages: You can't cheat! The color will stay there until you sand the low spots out. (Well, you can cheat by cleaning it with lacquer thinner ; ) )
The advantages: Perfect professional smoothness and top notch hull performance. (dimpled surface is very bad for laminar flow on the hull and gives rise to premature turbulent flow and viscous drag ), in other words, you won't be as fast as you could be, for the same effort, (and NO, the varnish will not fill the low spots).
Wet sanding. To spread out the sanding tasks a bit, I am getting a jump start on the varnish preparation on this hull. The deck is not even built yet.

Instead of flipping the assembly back and forth to do the various building tasks, I am 'killing two birds with one stone' so to speak. The mold hasn't moved once and there is nothing more to be done on the hull except to put on varnish.

You can see the magic marker high spots disappearing. The other side is already sanded (note: few shiny spot left behind !).
If you build the same way I do, You will encounter three types of fiberglass trimming. The one in the photo comes after the hull is fiberglassed.
I leave the overhang on until all wet sanding is finished. This shields the raw wood from water. No masking is needed here.
This second type, is done on the deck. Note that the deck was built from the sheerline of the already glassed hull. The only way to prevent the epoxy from fusing the bead and cove sheer together was to tape it.

The black drip skirt guides epoxy runs and water from wet sanding away from the hull. See the top photo.
At last, scoring the glass just above the masking tape allows you to peel everything away cleanly. The outside of the deck was wet sanded and is also ready for varnish.
The last type of fiberglass trimming will be done on the inside of both hull and deck. Be careful not to rip off the fragile coves of the sheer strip when you peel off the protective masking tape.

As I mentioned before, a small band of the sheer strip will stay raw, but that will be taken care of when the shells are taped and bonded together later.

Note the strip of carbon cloth reinforcing the rounded fillet in the stems. Normal glass tape is fine also.
Speaking of fillets, any sharp cornered voids such as the inside stems must be filled prior to glassing with lightweight epoxy slurry, otherwise the cloth will not adhere.
'Smiling' Cape Ann Expedition ready to leave the mold. The shallow deck is always easier to remove.


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Vaclav Stejskal
10 Colonial Court apt. 73
Stoneham, MA. 02180
Tel:  781-481-9261


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Last page update: 11 January 2020