Fixing leaking fixed portlights

[KWKloeber]

Sorry to resurrect an old post here but I am planning to to reinstall my aft windows/port lights
I read that a combo of the 3H VHB/Dow 795 is not recommended by those who have tried but I was wondering whether a 3H VHB/Butyl tape combo might work any better.? I was thinking the tape would provide the adhesion qualities needed and then if I ran a generous bead of butyl next to it it would provide the water proofing/gap filling qualities?

The VHB doesn't have enough long-term holding oomph (for the butyl tape, which has to be held in tight compression (as in under a deck fitting) in order to not fail from weathering, etc.)

The way to go is 795 with the plexi temporarily held in place by internal suction cups, or external duct tape or wood blocking.  You don't need (in fact you don't WANT) compression during the cure - just held in place.

[Whiskymac]

Ok thanks for the reply.
Maybe I could use small pieces of the tape to hold window in place while the 795 dries as well as providing the spacing?

[Jon W]

Noah and I teamed up to remove and replace our fixed portlights. The toughest part of the job is removing the old in a good enough condition to be used as a template for the new portlights.

We used DOW 795 with small pieces of foam as spacers. The portlights were held in place with the screws from the originals while the DOW 795 cured.

According to Andy at Boatworks Today, VHB tape is the way portlights are installed on new production boats. The VHB has no forgiveness. That's why we used the adhesive/sealant spacer method.

[Noah]

I second what Jon says however, even when manufactures do use VHB tape to hold the windows in, they apply a bead of caulking on top—around the edge of where the plexi meets the fiberglas, to serve as a seal against water intrusion.