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  #1  
Old 06-26-2010
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UV resistance in sealants

My relatively new to me boat had the hatch (acrylic?) window part replaced before I bought it last year. It leaked a bit last season, and this season the sealant has failed completely and the window comes right off the frame when opened.

I've asked the yard that did the work in the first place to fix it. The said they would but they haven't got a round tuit yet.

My question is why the seal would fail so badly so quickly. I can see the initial small leak having been from missing a bit of bead on the caulk job or whatever, but for the entire seal to fail in a year seems to suggest a problem with the sealant. Could they have used a sealant which degrades that quickly in sunlight? Could it simply be the sealant wasn't adhesive enough or is incompatible (eg. LifeCalk polysulfide)

The stuff is black (matching the rubber window-to-frame gasket) and still somewhat flexible.

Assuming the round tuit is still backordered at the yard, I'll probably just fix it myself. I'm thinking either LifeSeal (silicone/polyurethane blend) or just a straight silicone like 3m. Presumably the LifeSeal will be more adhesive, but I can't find anything about UV resistance.

Anyone else had this problem?
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Old 06-27-2010
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What sealant did they use. Ports need to be bedded with the right sealant. It sounds more like they failed to properly clean and prep the acrylic or used the wrong sealant than anything else.

Acrylic glazing on boats should generally be bedded with Dow Corning 795 or Sikaflex 295 with the 209 primer. I generally recommend the DC 795, which is a structural silicone adhesive specifically designed for bedding glazing.

DO NOT USE ANYTHING ELSE... it will fail.
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Old 06-28-2010
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My guess is that they didn't clean things up right and bedded onto the very least amount of dust or something. Agreed on the sikaflex there, should stand up well if applied correctly.
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Old 06-28-2010
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Sounds like the used plain black silicone seal from the hardware store, which will let go of most plexi in a couple of months.

It is also unusual for glazing on a boat to just be "glued in" to a frame without any mechanical clamping or attachment. That just sounds wrong.

Brand name on it? Pictures?

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HS—

The glazing that is bedded in Sikaflex 295 with the 209 primer or in Dow Corning 795 does not require any mechanical fasteners as a general rule. They're both structural adhesives and should provide plenty of strength to the glazing joint when properly applied.
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