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Building my own kayak (2) – Shaping and reinforcing the foam plug

August 6, 2013

Before writing about the current progress I like to complement my previous post with these images about the individual foam slices and a partial foam plug:

After I have glued all foam slices together I did a lot of sanding in order to even out minor irregularities of the foam slices, for shaping the bow and stern, making the plug as symmetric as possible, adding the recesses for the hands behind the cockpit rim for simpler getting out of the boat and for shaping the cockpit rim. Sanding the foam was more difficult than I expected – I ended up with lots of little holes and regions with a rough surface due to applying to much pressure when sanding. Also, I noticed that the foam has a preferred direction for sanding (note to myself: next time cut out all slices in the same orientation from the big foam sheets), resulting in scratches at the transition between two slices. For sanding, I used sanding paper from grit 60 to 120, mounted with double-sided tape onto small pieces of styrodur foam with different shapes (planar, convex, concave, or a particular shape that was used to go around the cockpit rim) . In order to fill the holes and scratches I have applied putty. I found the water-based stuff that is used to fix minor cracks in walls to be perfect for this: it does not smell, it is cheap, it is easy to sand and it does not interfere with epoxy. All in all the sanding and filling of the foam plug took me 20 hours.

After that was finished I have applied two layers of 160g/sqm glass on the hull and the deck. After glassing the hull I have wrapped plastic foil around the entire boat, resulting, in theory, in a smooth surface. In practice, some wrinkles had formed due to the plastic wrap, which can be sanded down anyway. A rather big problem was that a large bubble at the concave spot between the legs (see pictures of 3d model in previous post) has remained unnoticed until I unwrapped the foil. As the resin had already cured at this point I needed to cut out the glass in this area and redo it.
The deck was even more problematic: I decided not to use foil again as the deck had multiple concave areas (between foot bumps, the area between the shin bones, the recesses for the hand and the cockpit rim). I have applied epoxy on the plain foam first and have let it cure for a few hours until it was tacky. The idea was to get a sticky surface in order to enable a simpler application of the glass cloth. Indeed the cloth was sticking better to the foam than when using fresh epoxy. Still, it was quite difficult for me to get a satisfying result without any air bubbles. After around 3 hours of removing air bubbles by applying pressure using a brush or cutting little rips into the cloth using a knife I was quite happy with the result. I was checking every few hours in order to assure that no new bubbles have formed. I  let it cure overnight and in the morning I was disappointed that the resin has only cured partially. As I have mixed multiple batches of epoxy for glassing the deck, one of these batches must have had too much of either resin or hardener. I found out that only the outer layer was tacky whilst the inner layer of glass has cured more or less properly. I have removed the outer layer at the places where it was still tacky and tried my best at removing the sticky epoxy using alcohol (for cleaning 🙂 ), a cotton cloth and peel ply. Still I was not able to remove all of the bad epoxy. After consultation with Jim Snyder, thanks again for helping me with this, I have applied a new layer of glass with properly mixed epoxy. In total, the glassing and the repairs I had to do due to my lack of experience took me around 14 hours. Here you can see a few pictures:

The next step will be to prepare a smooth surface in order to create a mold with the plug. I have made some experiments on my miniature boat using fine putty, spray can filler used for car varnish preparation and lots of sanding. I am a bit worried that even the very small boat needs so much sanding. For its big brother I will have some support from an orbit sander, however, it won’t be able to work in every corner. Here you can see the miniature model after two layers of fine polyester putty and lots of sanding:

Using the automotive filler in a spray can I expected the pinholes and sanding scratches to disappear. However, the result was not as expected, yet. I will try to use an additional very thin layer of the fine putty, sanding with a higher grit and then apply the filler.

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