Butyl Tape and leaking port-light
After reading Maine Sail’s contribution on butyl tape, I thought it might be the way to solve a leak I have in an existing port light assembly but I want other people’s opinions on this since I have never done a job like this.
The assembly comes in two parts. The window unit is an aluminum frame with the glass well sealed into it. No leak there. The frame has a ~1/2” “flange”, can’t think of a better word, all the way around the inside at right angles to the frame. This flange fits into the window cut-out of the cabin, or in other words, in the hole that was cut out of the fibreglass. This window unit is held in place by frame inside the cabin, which is screwed directly on to the outside frame.
The leak comes from where the outside frame butts against the fibre-glass of the cabin. Whatever caulking had been used has failed and I was thinking of re-caulking it with the butyl tape.
Problem one is that there are small but obvious gaps between the outside aluminum frame and the cabin surface.
Problem two is that the inside of the cabin is a fibre-glass liner and so the window assembly is sort of clamping the liner to the deck/cabin structure. There is probably some movement between them.
Problem three is that the previous caulking was a sort of rubbery, translucent kind of stuff that stuck mainly to the aluminum and not the fibre-glass of the boat. Does this sound like some kind of silicon-based product?
From my too-long description, does it sound like butyl tape is the way to go? If not, any suggestions?