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Old 11-01-2015, 16:38   #1
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Re: Bedding a deck prism?

I've got two glass prisms built into my deck and both have started leaking. Any suggestions as to how to get them out safely with out breaking them and what to use to rebed? Hate to screw it up as I'm sure they aren't the easiest things to replace.
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Old 11-01-2015, 18:03   #2
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Re: re bedding a deck prism?

We have two 3x8 prisims in our teak deck , they have a bronze trim ring that was removed and carefull use of utility knife and reeding tool ( bent screwdriver) removed them . Cleaned up then re-bedded with sikaflex (271 I think )
All good after 3 years in rain capital Seattle , lol
Cheers, Stonefloat
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Old 11-01-2015, 18:14   #3
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Re: re bedding a deck prism?

Quote:
Originally Posted by Stonefloat View Post
We have two 3x8 prisims in our teak deck , they have a bronze trim ring that was removed and carefull use of utility knife and reeding tool ( bent screwdriver) removed them . Cleaned up then re-bedded with sikaflex (271 I think )
All good after 3 years in rain capital Seattle , lol
Cheers, Stonefloat
We had two on our last boat also with teak decks and they leaked. Had to rebed them once a year but we were in the tropics. We used the exact same method. Unscrew whatever screws hold the border (if there is one) in the deck. Remove it and with box cutters and a new blade or two take out all the bedding material. Remove same from prisms themselves. Be careful not to slice the teak if you have any. Tape the perimeter (you could have done this first too) and then rebed using generous amounts of Sikaflex (I believe we used 271 also). Finally, with a wet finger smear the Sikaflex smooth and press it into whatever bubbles or gaps may be around the prism and deck.

If you need a haircut don't get one before you do this job. That Sikaflex gets everywhere so you might as well go see the barber when you're finished.....

Clean your hands and crack open a beer while you let it cure.

It's easy to do and with a little practice doesn't take long.

Dhillen
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Old 11-01-2015, 18:15   #4
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Re: re bedding a deck prism?

I have had deck prisms as well and had to rebed them in the past. The good news is that there is a new product that I have just used as I am rebedding my fixed ports. Its a spray that will weaken the bond on 5200 which is normally almost impossible to get out and it weakens the bond on most of the common sealants. It is called Marine Formula by Debond Corp. So dig around it a bit, spray with this new product and it starts to get pretty easy after that. Rebed with 4000 or similar.
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Old 12-01-2015, 09:58   #5
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Re: re bedding a deck prism?

We did ours this summer. Removal was easy, I sliced existing bedding with utility knife after removing trim rings, then my wife pushed up from below while I gently trimmed the last bits that were holding it. Both came out easy. No hard objects near the glass... i.e. don't try to pry it up...or it will break. Our deck is cored but was dry so I just I treated the opening with penetrating epoxy for additional protection after careful removal of all old sealant. Then assembled with Sikaflex 271. As an aside ours leaked because it was cracked. I was able to find someone locally who pours his own. The replacement is dimensionally correct and the edges are not as sharp as the original so hopefully better resistance to being chipped or broken if something strikes it.
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Old 12-01-2015, 19:52   #6
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Re: re bedding a deck prism?

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We did ours this summer. Removal was easy, I sliced existing bedding with utility knife after removing trim rings, then my wife pushed up from below while I gently trimmed the last bits that were holding it. Both came out easy. No hard objects near the glass... i.e. don't try to pry it up...or it will break. Our deck is cored but was dry so I just I treated the opening with penetrating epoxy for additional protection after careful removal of all old sealant. Then assembled with Sikaflex 271. As an aside ours leaked because it was cracked. I was able to find someone locally who pours his own. The replacement is dimensionally correct and the edges are not as sharp as the original so hopefully better resistance to being chipped or broken if something strikes it.
WULF has the right Ideas but the best way to remove the DECK PRISMS is to do as he suggests re the old sealant but rather than trying any prying use a bottle hydraulic jack from the deck below and a 2x4 with the end v'd to match the prism"s lower side shape and after you are sure your bedding cutting is complete add a small stroke every 5 minutes or so and it will pop out easily if the sealant has been properly cut . For those of you needing heat annealed round or rectangular glass prism replacements or any of their related parts I manufacture them . Also the best "no leak "sealant for glass to metal or fiberglass or to epoxy is G.E. DOWCORNING "SILPRUF" I HAVE BOTH USED IT EXTENSIVELY ON GLASS PRISMS AND METAL AND LEXAN AND HAVE HAD GREAT RESULTS ....NEVER USE 4200/5200 YOU WILL HAVE LEAKS ....cheers R. .....marine skylights vic. b.c. Canada
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Old 12-01-2015, 22:23   #7
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Re: re bedding a deck prism?

I'll be using DOW corning 795,i have some leftover from my fixed ports. Here's a comparison of it to other products.

https://www.google.com/url?sa=t&sour...AnrV2r6EwMJBQg

- Ronnie...on the geaux
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Old 13-01-2015, 00:37   #8
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Re: re bedding a deck prism?

Be careful - the Dow 795 has a shelf life. Check the expiration date on the tube. DONT USE IF EXPIRED! It will just stay gooey and never cure.

Not fun.


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Old 13-01-2015, 02:22   #9
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Re: re bedding a deck prism?

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Originally Posted by the_alpine View Post
Be careful - the Dow 795 has a shelf life. Check the expiration date on the tube. DONT USE IF EXPIRED! It will just stay gooey and never cure.

Not fun.


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Yea, thanks for the reminder! I may not have even have enough left over. Probably a good idea to just get a new tube.

- Ronnie...on the geaux
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Old 13-01-2015, 05:32   #10
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Re: re bedding a deck prism?

Greetings and welcome aboard the CF, jrossbruce.
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Old 13-01-2015, 21:36   #11
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Re: re bedding a deck prism?

I second the Dow 795. If the trim ring bends a bit removing it, take it to a flat area of concrete, and tap the heck out of it gently with a hammer, to flatten. Don't hit so hard it marks the trim. Hundreds/thousands of easy taps. Learned this from our car guy, who does body work. It takes a while, but really, really works.
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Old 16-01-2015, 04:04   #12
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Re: re bedding a deck prism?

Any problem using Sikaflex 291 instead of 271? It's not available out here.
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Old 01-05-2016, 09:43   #13
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Re: Bedding a deck prism?

We are finally in a place where we can take out our prisms(having the teak deck removed finally)and we've found that our prism seems to be different from ones in the earlier posts. We cut the sealant around the prism and then chiseled the teak out from around the metal collar. After my wife cut around the inside of the collar through the sealant, the prism just popped right out. The inside edge of the bracket is beveled so the prism just rests in it, not holding it down. Only thing that keeps my prisms in place is the sealant and gravity.
Once the prism was out, I slowly sliced under the bracket till it popped free of the deck. I'll get the rest of the sealant that stayed attached off later but it surprised me that my assembly was so different from what other sailors have written about theirs. Boat dates from 1982
Suggestions on how to reinstall it would be appreciated since its not really held in by anything.
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Old 01-05-2016, 10:13   #14
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Re: Bedding a deck prism?

mestrezat-
You can use free software and an online machine shop, or make a paper tracing and take it to any local machine shop, and ask them to cut a trim ring, i.e. of stainless or bronze as you please, to place over your prisms and screw down into the deck, to secure them.
Or you can simply put them back in as they were, secured by an adhesive caulk chosen to match the materials, with a primer if that's also recommended. Bear in mind that in the 1980's "glue" was not as commonly trusted as it is today. "Glue" holds the wings onto combat aircraft, so it certainly can hold down a deck prism if done according to the manufacturer's recommendations.
But having trim rings cut from a suitable metal and then screwing them down, setting them flush into the deck, certainly will be simple enough--even if it does mean a good deal more work and expense.
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Old 01-05-2016, 20:22   #15
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Re: Bedding a deck prism?

If you have the time, I posted pictures on our blog on Sailblogs. Do a search for Zephyr. It will take you right to our posts. Been doing them for over eight years now. Ever since we moved on board.
Thanks for the help and info.
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