Our metal skylight with a double-glazed panel (lined inside with timber) is leaking from a corner. We tried silicon but this didn’t resolve the problem. It is on an Aintree sail away. Any advice would be appreciated.
TONY REPLIES: This is not an expensive builder so we need to bear in mind that some compromises may have been made construction wise. It looks as if there is a steel up-stand all around the aperture welded to the boat’s roof. I say this because I can see what looks like weld blobs along seam A but you need to check, they could be blobs of sealer. The first thing to do when you get to the boat is to probe those blobs with a small screwdriver to see if they are hard - weld, or have some give in them - sealer. If the blobs are weld then unless they have a pinhole there should be no leaks from that joint.
I can’t see from the photo if the frames for the lift up portions are wood or steel or how the glass is retained but what immediately grabs my attention is that the glazing is set below the frame so rain will pool along the bottom edge of the glass. This is asking for leaks unless the lower lip extends beyond the water level as shown in this diagram:
You say water leaks in from one corner, I bet it’s the rear lower corner on one side, exactly where water pools with the boat normally trimmed a little stern down.
I can also see what looks like copious
amounts of sealer all around the joint where the frame meets the glass. Applying sealer externally like this is unlikely to effect a long term cure, especially as there will be an expansion-contraction difference between the glass and frame. In the case of a wooden frame this will not only be caused by temperature but also humidity. I can’t see how the double glazed units are fixed into the frames but I would expect that there would be a thin securing frame above or below the glass on the inside, probably secured with screws.
On the present information I suspect the glazed units will have to come out and all the old sealer removed. If they are metal frames all the rust removed, treated, primed and painted because rust takes up nearly ten times the volume of the steel it formed from so it forces a gap through which water can leak. If the lift up frames are steel you may also find the welds at the corners have not been ground flush so it holds the glass clear of the frame. When you refit the glass use either butyl strip or closed cell rubber strip as sold to seal window frames to the boat side rather than silicon or any other gunned sealer. If you must use a gunned sealer then apply, tighten the fixings until excess is squeezed out all around. Then let it cure and tighten further. I fear this may turn out to be a job that needs doing every few years.