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Old 17-12-2006, 14:51   #1
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Silicone

Quote:
Originally Posted by ssullivan
This may warrant a different thread, but why? I used silicone and it hasn't leaked in the 12mos since I bedded the items. If anyone has an opinion on that, and can show me why I shouldn't use silicone, we should probably start a new thread on the topic. Confused..
Figured I'd start the thread, Silicone is generally not a good exterior sealant, as it does not usually bond well to fiberglass and leaves a residue when removed so is hard to re-seal over in my experience.

I do use marine silicone below decks for example when re-sealing the edges of the shower stall or working on filling holes in the fridge etc, just not in areas that get UV and/or exterior water. I find that specialized sealants such as 4200, lifecaulk, lifeseal, silkaflex products work better for those bedding/adhesive jobs.
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Old 17-12-2006, 15:14   #2
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For bedding I would agree Jon. You might get decent duty using silicone for a yeear but not 5 years. A good Silkaflex is good for that long and more depending on the application. Given the cost it seems a bit strange to not use the better bedding coumpunds. The trouble you go to to remove and clean items before re bedding them and then not use it seems far too odd.
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Old 17-12-2006, 17:41   #3
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Had experience using real cheap silicone on some boat windows. This was branded as Roof and Guttering sealant.

The boat came back in for some repairs about 5 year's later, where the owner had mounted fittings in the cabin without epoxy sealing the timber core which rotted out.

Anyway, pulling the windows off actually pulled fiberglass off of the timber core of the cabin, so I have been using this stuff ever since on windows.

Dave
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Old 17-12-2006, 18:10   #4
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I think the reason some use silicon sealer on plastic ports is that they don't want to use 5200 and make them permanent and polysulfide is not compatible with plastic.
Isn't there someone else with this experience?
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Old 17-12-2006, 19:49   #5
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Quote:
Originally Posted by SkiprJohn
I think the reason some use silicon sealer on plastic ports is that they don't want to use 5200 and make them permanent and polysulfide is not compatible with plastic.
Isn't there someone else with this experience?
Kind Regards,
JohnL
Yes, this is what I know from the company Beckson that makes my ports. Using any other bonding agent will actually void the warranty. Silicone also has excellent "rubbery" property which allow it to flex when there is a load between the surfaces. These are what I was told by the port company, and what I have observed in practice. I'll keep the board updated annualy on if my ports leak.

But sorry if this post is a little loopy. I'm still a bit woozy from Scromboid (or whatever) poisoning. Ugh....

Better and more questioning reply in the AM.

Jon: I agree with you about the bonding properties of silicone. It's my understanding that it isn't bonding at all, rather forming a rubbery, watertight gasket instead. Sometimes it does stick, but nothing I have had any trouble removing (even the original silicone that was on the ports from ages ago). I removed it with a plastic scraper and in extreme cases, a touch of the finest grit sandpaper around.

To be clear: I am using marine grade silicone bought at West Marine, not some garbage from a hardware store.
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Old 17-12-2006, 20:29   #6
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I am replacing that lenses in my hatches and I called Bomar to see what they use. They sold me GE UltraGlaze silicone for $28. a tube. I used Sikaflex for my windows last year and it worked very well.
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Old 17-12-2006, 23:35   #7
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There are many types of silicon sealants as well. The two major different ones are neutral cure and acid cure. But withn those, there are many sub types each formulated for different uses.
DO NOT use acid cure on Aluminium, Galv or SST.
Silicon should only be considered as a sealant. It is not a good adhesive in many situations.
There are many potential problems with silicon sealants. One is the silicon it's self. This is a problem on painted surfaces if repaint is required. However, there are cleaners and paint additives available today that helps the situation.
Silicon can have problems with mold growing on it.
Silicon can have issues with small "pinhole" leaks appearing in and around the seal after some time.
Most glaziers nowadays use a new product called MS short for modified silicon sealant. this is a very different product and not subject to many of the problems I listed above.
It reply to the movement issue Sean, MS and urathane adhesive sealants all have a good playbility when cured and should move enough to ensure stresses do not break anything. The major added advantage with urathanes is there great adhesive strengths. I don't like the idea of a window coming out untill the day I want to remove it. And then it not too hard to cut.
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Old 18-12-2006, 02:42   #8
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Personally I found either a glazing silicone or a Silkaflex modified silicone the best for Plexiglas portlights. I have made the mistake of using 5200 a very long time ago on one and it came of in very little pieces.. but we learn from our mistakes especially the difference between adhesive and gasketing.

Also FWIW Practical Sailor recently did a report on caulks...
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Old 18-12-2006, 02:42   #9
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Personally I found either a glazing silicone or a Silkaflex modified silicone the best for Plexiglas portlights. I have made the mistake of using 5200 a very long time ago on one and it came of in very little pieces.. but we learn from our mistakes especially the difference between adhesive and gasketing.

Also FWIW Practical Sailor recently did a report on caulks...
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Old 18-12-2006, 05:22   #10
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Quote:
Originally Posted by Alan Wheeler
The major added advantage with urathanes is there great adhesive strengths. I don't like the idea of a window coming out untill the day I want to remove it. And then it not too hard to cut.

Ahh.... here lies the difference. I use my bedding compound to seal out water, not to work as an adhesive. I use the screws to keep the port/whatever in place. Maybe it's two different schools of thought?
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Old 18-12-2006, 07:01   #11
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Quote:
Originally Posted by ssullivan
Ahh.... Maybe it's two different schools of thought?
Not so much differing schools of thought, as different methods of construction.

The more elegant fastenerless adhered glazing requires a structural adhesive, whereas the bolted glazing only requires a sealant gasket.

Screws are an inadequate fastening.
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Old 18-12-2006, 07:04   #12
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Quote:
use my bedding compound to seal out water, not to work as an adhesive. I use the screws to keep the port/whatever in place. Maybe it's two different schools of thought?
No I don't think so. Very few attachments aboard rely on only an adhesive. Just about anything uses a mechanical fastener along with various sealants and bedding material. I would see glazing as a separate situation but attaching metal framed ports would have both situations. There is the glazing and then there is the attachment of the frame. Each is not performed the same way.

Deck hardware requires bedding but also attachment. The two are different we all would agree and both are required. the types of bedding for the specific situations is where we all might choose one product over another.
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Old 18-12-2006, 07:44   #13
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GLAZING:
C&C Yachts featured very elegant, flush mounted, frameless, sidelights with no mechanical fastenings.
I believe the structural adhesive was a methacrylate.
Over the 17 years we knew her, “Southbound” (1984 C&C29) never leaked a drop through the glazing.
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Old 18-12-2006, 09:20   #14
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Ahhh... now we're getting somewhere. Indeed, we are talking about two different applications. Sure, you when you need to bed say.. a winch, you would not use silicone. When I bed my hatches, I did not use silicone. But when I did my plastic ports (which are held by all the
screws in place), I used silicone as the manufacturer demanded.

I have also used silicone in other applicaitons where I was simply "plugging up" a leak, such as around the mast boot.

The above posts are correct... different tools for different jobs, I suppose.
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Old 18-12-2006, 10:10   #15
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5200

As I remove various bits from my boat. Like the toe rails and other types of hardware. I have noticed that it has been bedded in a white ply-able and very sticky compound. This stuff holds together really well. My boat was built in 1981 and the bits being removed are original. So this stuff which I assume to be 5200 is still elastic ply-able and sealing well. If I leave any of it laying around and step on it, it will stick really well to my shoes. Now it does require being careful as not to damage the parts being removed because it sticks to well. I am impressed and will use it again for bedding in hardware such as port light, hatches (new SS) and toe rails etc. All of these items will also be attached with mechanical fasteners. Does anybody have a comment on 5200 from what I have seen it does not harden or become brittle it's just really sticky or maybe this is another material?

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