using Dow Corning 795 Silicone to caulk glass-gasket joint in portlight

[davisr]

I'm wanting to hang on to my original aluminum-framed portlights with tempered glass. I plan to rebed the portlights to the exterior of the cabin with butyl tape. This question does not concern that part of the job. Instead it concerns the gasket that holds the glass within the frame. I want to avoid a complete rebuild of the portlights, since the Wefco gaskets are not cheap, and it's not very easy getting everything back together. A recent thread addresses this difficulty http://www.ericsonyachts.org/infoex...11765-Leaky-windows-on-a-1978-27-foot-ericson I read on an older thread a posting by Tenders, who was advised by a specialist, that it is preferable to avoid this disassembly and instead to apply Dow Corning 795 Silicone to the joint between the glass and the gasket http://www.ericsonyachts.org/infoex...Ericson-27-remove-clean-and-re-bed-portlights My question is this: Has anyone ever used 795 Silicone to seal this joint, and if so, you have had any success? Attached is a drawing by a fellow E25 owner of the profile of the E25 portlight. I believe this is the same or similar to that of the E27 and E29. Thanks, Roscoe.

 

[Christian Williams]

This may not help, but somebody here took their fixed portlights to a glass shop and the shop had common gaskets that fit fine.

I can't find the thread, it may be lost to the hacking.

 

[davisr]

Thanks Christian. I might end up trying something like that. Presently, the glass, as far as I can tell, is firmly seated in the gasket. Even if I installed a new gasket or had someone else install it, there would still be a need for a bead of Silicon between the glass/gasket joint and the outboard edge of the aluminum frame. The existing silicon is indicated in purple in the diagram below. The existing silicone has cracks in it and appears to be suffering from dry-rot in some places. I'm just curious to know if anyone else has been able to get away with simply laying down a new silicone bead on the old gasket rather than rebuilding the portlight with a new gasket (and then laying down a new bead). Either way, I have to lay down a bead. I'd prefer to do it on top of the old gasket, since the old one is still firmly holding the glass in place.

 

[Walter Pearson]

I used Dow 795 to seal that area in E27 portlights in 1999. I don't have the boat any longer, but I believe there have never been any leaks.

 

[davisr]

Many thanks Walter. I'm glad to know that someone out there has tried this and found it to be a suitable fix. I think it's about time to dig out that old caulk and give it a shot.

 

[Walter Pearson]

I should add that I made a special knife that I could cut away some of the old extruded gasket in order to provide a little more volume of silicone and more surface for adhesion in between. That diagram is nicely done and does represent the geometry in my E27. The difference in my case is the overlap of the frame with the outer fiberglass was almost non-existent in some areas as the cutout was poorly done. I used a combination of a narrow strip of foam tape on the inner perimeter and sealant outside of that. The foam tape was essentially a dam to keep the sealant from oozing too much to the inside.

I also filled the gap between exterior and interior with filled epoxy. This gave me a more solid perimeter to pull up the the interior frame and also would keep other deck leaks from coming out at the portlights. If there were leaks at the portlights, I would only suspect the sealants somewhere had failed. I suppose the argument might be the original foam tape sealing method allows some degree of moving or adjustment to stresses, but I never had a problem with tape plus the sealant combination.

It also should be noted that there might have been two thicknesses of glass used on these boats. The gasket described above did fit my boat, but some owners had difficulty with some seals and it turned out that the dimensions were not the same and appeared to be made for this frame but with thinner glass.

 

[davisr]

Thanks so much for this additional information Walter. I think I'm going to use the method you describe to cut out a little bit of the gasket in order to have a little more room for the silicone. Fortunately, all the portlights fit snugly into the cuts outs, so I won't have to deal with those issues your describe. I guess it all evens out for everyone. I've had to deal with other factory errors here and there in other parts of the boat.

 

[e32stx]

a Lil late but

795 is perfect for the job, used it on an e27 and e32. I'm in the marine industry and that is what we use.
1.Simply take apart your frames and glass.
2.Clean off old sealant w/scraper and wire wheel, left over rez w/toluene.
3.Take some of the old gasket that goes around the glass and cut into 2" pieces.
4.These will be used as spacers to center the glass in the frame.
5.Be sure to trim them down along their length to keep them from protruding above the frame channel.
6.Run a good bead of 795 (but not too good as this stuff is not Cheap and allot will mush out when ports are put together) along each half frame channel.
7.Mount old gasket "spacers onto top and bottom of glass and mush glass down slowly into the lower frame half.
8.Don't forget to install ur frame couplings to both sides of frame!
9.Now with upper frame half's channel filled with goop, slide IT down onto the glass making sure to align ur tabs/couplings.
10.Put the 2 screws back into either side of the frame.
Now the fun begins
11.With a gloved hand (never bare fingers) use ur finger smooth the goop all the way around the frame, forcing it down as u go.
12.Repeat on opposite side.
Finally. Cleans up easily with mineral spirits.
Practice on a small portlites first.

Cheers
Ollie