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Thread: Bedding Deadlights w/ Butyl tape, DC795 and Screws Reply to Thread
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  Topic Review (Newest First)
2 Weeks Ago 07:01 AM
DonScribner
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

What you're talking about is what we in the industry call a "structural glazed joint". Skip the screws. With VHB they are not required. Set the VHB 1/4 inch back from the edge, adhere to the cabin, mask all surfaces, motor in the 795. Now TOOL the joint. Never listen to anybody that says they don't or that it isn't required. Remove masking tape immediately. Go to any big city and look up. Much of that glass is held in this way.


I just brushed over the process but if you search for it on any of the sailing forums, you'll find me preaching about it on many occassions. Another guy posted a real nice page with photos and everything. Made me jealous.
2 Weeks Ago 07:43 AM
rckfd
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

I owned a j/30 for twenty odd years it was a good boat. Like C&C and Cals of the time it had those fixed side ports bedded in some sort of goop that failed after x amount of years. Removing the ports cleaning up the old sealant was arduous to impossible to remove. I talked to other owners of j'S C&c's and the like and found that it was an on going problem that no matter what you use or how you affixed them in x amount of years they ALL leak. So from the very beginning I took the regular maintenance and up keep look about it just like you do on chain plates. So every third year without fail I popped those suckers out cleaned up the old and re-bedded with tub and tile silicon and never ever had a leak. It was maybe hour and a half job and did the chain plates at the same time. I figure all that goop is just as bad as the next and it will fail and chose the one easiest to clean the old off with least amount of damage.
2 Weeks Ago 05:52 AM
copacabana
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

Butyl is great for this job, but you will find that over time more butyl will ooze out the edges. I did some of mine over a year ago and every so often I give the edges another clean up. No leaks though!
2 Weeks Ago 11:47 PM
Captncol
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

I'm looking at doing this job in the spring. A thought - your calculation of expansion is for the distance between two screws, whereas the greatest amount of expansion will be between the two screws that are furthest apart. That is about 33 ins not 5 ins. So the movement will be about six times your calculation. However, the substrate (the deck) will also get hot, almost as hot as the acrylic, and expand also but at a different rate. But as there are no leaks, what the hell, I'll copy you!
05-18-2013 10:48 AM
mmazour
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

Update - deadlights are installed and do not leak!
However my initial above noted installation method was slightly altered. While screwing down the deadlights the butyl compressed and extruded out beyond the edges of the deadlights. So I cut around the perimeter of the deadlight with a plastic razorblade and cleaned it up using the stab and pull method. This left me with no gap for the DC795 so I skipped it.
04-12-2013 10:57 AM
jsaronson
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

Common issue on C&c many people use two sided automotive tape and 795. No need for butyl for this job.
04-12-2013 10:45 AM
benesailor
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

I would add one thing. Any holes you drill in the acrylic i would machine/sand in a small radius on both sides to help avoid any cracking once tightened. Leaving sharp edges anywhere can lead to cracking down the road.

Quote:
I basically 'troweled' the 795 on so that we had full coverage of black 795 under the port light, tightened panel gently to avoid dimples as much as possible, then removed the excess before running the outer bead. Alternately you might consider painting the under-portlight area black first.
I think this may be the best coarse of action. Acrylic can have some movement.
04-12-2013 10:31 AM
Faster
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

Quote:
Originally Posted by mmazour View Post
This is the purpose that I thought the butyl tape would serve, spacer as well as sealant, for both the screws and acrylic.
I think the major difficulty with your intentions (and what you plan may well work fine...) would be the assurance that the 795 would indeed penetrate fully under the acrylic up to the butyl to create that 'gasket'.

One other issue would be aesthetic.. despite the darkest smoked acrylic you will still 'see' any lack of uniformity in the material between the cabinside and the acrylic. I basically 'troweled' the 795 on so that we had full coverage of black 795 under the port light, tightened panel gently to avoid dimples as much as possible, then removed the excess before running the outer bead. Alternately you might consider painting the under-portlight area black first.

I'll be interested to see how this all works out if you proceed with the butyl/DC795 combo...
04-12-2013 10:08 AM
mmazour
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

Quote:
Originally Posted by Faster View Post
I do have the deadlights standing off the cabinside surface 1/16 or so, allowing the 795 to create a full contact gasket.
This is the purpose that I thought the butyl tape would serve, spacer as well as sealant, for both the screws and acrylic.
04-12-2013 12:25 AM
Faster
Re: Bedding Deadlights w/ Butyl tape, DC795 and Screws

I've never used butyl in combo with DC795... but have had success with straight 795. I do have the deadlights standing off the cabinside surface 1/16 or so, allowing the 795 to create a full contact gasket. I followed it up with a bead around the outside as you described.
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