Leak­ing sky­light

Canal Boat - - BACKCABIN -

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.

Carol Bean­land

A

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.

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