Wednesday 29 August 2018

Thinking like water

I suppose gravity and surface tension are what mostly influence where water gets to. When fixing a leaky window, you have to imagine every route by which rain can get from the outside of the boat (Good!) to the inside of the boat (Bad!). That would seem to be (a) the edge of the window frame, (b) structural failures in the window frame, and (c) the holes for the screws attaching the frame to the hull. For the last week I've been going to sleep with images of the frame in my mind, tracing possible paths for the liquid enemy.

You also have to know what is available to keep the water where it should be. The canal forums are full of dire warnings about the horrors of silicone sealant, and the canals are full of boat windows treated by people ignoring that advice. Erin Mae's window had obviously received some attention from such people, who were not among those I thought of most favourably as I tried to remove the stuff. However, a suitable sealant applied in the right way has its advantages, and I decided on a belt and braces approach. First I used a self-adhesive neoprene tape.

Along the sides and the bottom I ran the tape along the edge – with care it was relatively easy to run it around the bottom corners. On the top edge I left a 2 mm gap, to fill later with sealant, and then went round all the screw holes, piercing the tape with a darning needle to facilitate the passage of the screw. Then it was time for the Sikaflex 221. It's a polyurethane adhesive / sealant.

I put a bead round the sides and bottom of the frame, in the space just inside the tape, and then inserted the frame into its position. I put a bead of Sikaflex along the top of the frame above the tape and began to tighten the frame.

I'd always felt it should be quite straightforward to seal the sides of the frame, and to locate and fill structural defects. It was the screw holes seemed to be vulnerable. I had already put a dollop of silicone grease into each screw hole, and now I put a dollop of Sikaflex on top of the hole as I inserted the screw. As it was tightened, the screw bedded down onto the sealant, hopefully making the whole thing water-proof.

Now in spite of its superiority (IMHO) to silicone, Sikaflex 221 has a tendency to get everywhere and stick to everything. I discovered that although soapy water is good for creating a smooth edge, a paper towel full of soapy water tends to smudge it rather than clean it off. My technique had also left black smudges around the screw heads. The technical data document advises that once it has cured, it can only be removed "mechanically".

I shall be able to cover the mess in the channel (more about that another time). But getting it off my fingers has been an interesting experience.


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