One of our starboard portlights started a minor leak last winter. It was nothing major and Victoria doesn’t get that much rain so i had left it ’till now. I replaced the gasket last year so i knew that it was a bedding/sealing problem.
The leaking portlight. You might be able to just make out a bit of staining below the lock knob.
Removing the frame. I find that using a socket wrench with the proper sized screwdriver bit results in less damage to screws and helps release corroded screws. You do have to be careful not to shear them if they are really seized.
Removing old sealant. It was easy to see where it had let go and water was coming through.
I found that using an Exacto knife worked best for removing old sealer from the gelcoat
After as much old caulk as possible has been removed, you can use a non-residue solvent to do a final clean of the gelcoat.
All metal frame surfaces have to be cleaned of old sealer as well.
Once all the old goo is gone you will need to dress up the oxidised metal. the new sealant won’t adhere well to powdery aluminum oxide. you can use a fine grit (220) sandpaper…
Or a dremel with a stainless or brass wire wheel. Don’t forget to do both inner and outer frames
Insert the inner frame back into the portlight opening and add a thick layer of silicon caulking to the frame and gelcoat. DO NOT use polyurethane adhesive like SIkaflex or 3M PL5200. if you do, future generations will curse you. Polyurethanes should only be used in situations where it will never have to be removed. As we all know, sooner or later this will have to be redone again.
Insert the outer frame and screws and tighten about 80% of maximum. wipe away all oozing caulk before it dries. Do not fully tighten screws.
Let the caulk cure for a few days and remove screws. the silicon has now formed a rubber gasket and when the screws are fully tightened it will compress the gasket, making a mechanical as well as a chemical seal. Even when the silicon loses it’s bond to the surfaces it will still seal.
But turning the screws will break their bonds with the caulking so fresh caulk must be squirted into the screw holes.
The screw holes have been filled with fresh silicon caulk and the screws fully tightened. Be careful not to strip the screws. This repair should last decades.