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1979 C&C 30 Mk I - 2QM15
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172 Posts
Discussion Starter #1
After reading through lots of posts here, I've gotten the message that in almost every case:

Boat + Silicone = BAD

So if silicone contaminates fiberglass so that nothing else will adhere to it; doesn't do anything useful for leaky windows; and should never be used to re-bed hardware...

Does "marine grade" silicone have ANY useful purpose? And if not, why do they continue to sell it in every boat supply store on earth?
 

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Don Radcliffe
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398 Posts
Silicone causes marine painters fits, but if you are not planning on awlgriping anytime soon, it is probably the best compound for bedding windows and hardware which you want to be able to remove. It works better when thicker, allowing for some expansion and movement, so countersink the holes when you are mounting hardware, and don't squeeze it all out when you are bedding windows.

The best silicones I have used are the 'neutral cure' ones, but the US doesn't seem to have heard of them.
 

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midlife crisis member
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975 Posts
Does "marine grade" silicone have ANY useful purpose? And if not, why do they continue to sell it in every boat supply store on earth?
What they sell at a store has nothing to do with whether it is a good product for a specific purpose, and everything to do with whether people will buy it. If people want silicone, a store will have it available, lest the go elsewhere to buy it.

Eric
 

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Boat + Silicone = BAD?
Silicone might be okay in the northern climes, but down on the Gulf Coast where boats are in the water year, even the best marine silicone is worthless. In the brutal summer sun and humidity it turns black, and looses it's adhesive qualities - you can pull it off by hand. Use either 3M or BoatLife caulking.
 

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midlife crisis member
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975 Posts
I think "boatlife" is a hybred. It's supposed to be pretty good for bedding plastic hardware, such as acrylic or polycarbonate portlights.
 

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Glad I found Sailnet
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I think "boatlife" is a hybred. It's supposed to be pretty good for bedding plastic hardware, such as acrylic or polycarbonate portlights.
Can I use it for my leaky hatches? I really don't want to spend $500 getting them re-done this year. I'd rather smear something around the metal to polycarbonite (?) junction (inside and out maybe) and forget it -- even if it means doing it agian next year. Boat is in southern New England. Lewmar hatches.
 

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Telstar 28
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1,000 Posts
I wouldn't use silicone for this... given that most "quick repairs with silicone" look like crap and work about as well.

Can I use it for my leaky hatches? I really don't want to spend $500 getting them re-done this year. I'd rather smear something around the metal to polycarbonite (?) junction (inside and out maybe) and forget it -- even if it means doing it agian next year. Boat is in southern New England. Lewmar hatches.
 

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I'll use whatever the advice here is. There just has to be something that works, even if it has to be replaced every x months.
 

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Boatlife makes Sillycone and polysulfide (Life-Calk) and a combo (LifeSeal)

It use to be fun when they were down the street as i use to repiar there tube filling machines and stock-up


My boats PO used most everything and the only downside i have seen so far is you REALLY cant get the Sillycone OFF to the point of lifting gel coat :( BUT it did NOT leak
 

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ASA and PSIA Instructor
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4,101 Posts
All sealants have their proper and/or preferred uses, and silicone has a number of such on boats...usually where flexibility, removeability and thickness are important criteria. FWIW what comes to my memory are the OEM instructions for Beckson opening ports and replacement lens for several hatches ( see DIY-BOAT.COM - Hatch Lens Replacement 4/20/01) which specified to use only silicone as sealants.
 

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midlife crisis member
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Bene,

If you eventually plan to replace the deadlight just use silicone to seal it up as best you can. If the surfaces are clean I imagine it will stay there for a year. You are sealing between the plexy and the aluminim frame correct?
 

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ASA and PSIA Instructor
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4,101 Posts
If your issue is that the lens in a hatch is leaking, then you should just remove and rebed the lens...using only silicone, unless the OEM has a different specific recommendation. It's a simple job, the work is mostly removing the old sealant from the lens and the alu frame. Get those clean, and resetting the lens is a piece of cake, and it will last for many years. Smearing a coat on top may not be successful, and is not likely to look too good.
 

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Telstar 28
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And if you take the time to do it right immediately, you won't spend all the time trying to fix it later, or fix the damage from the leaks the half-assed approach will leave you to deal with.

If your issue is that the lens in a hatch is leaking, then you should just remove and rebed the lens...using only silicone, unless the OEM has a different specific recommendation. It's a simple job, the work is mostly removing the old sealant from the lens and the alu frame. Get those clean, and resetting the lens is a piece of cake, and it will last for many years. Smearing a coat on top may not be successful, and is not likely to look too good.
 

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Glad I found Sailnet
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If your issue is that the lens in a hatch is leaking, then you should just remove and rebed the lens...using only silicone, unless the OEM has a different specific recommendation. It's a simple job, the work is mostly removing the old sealant from the lens and the alu frame. Get those clean, and resetting the lens is a piece of cake, and it will last for many years. Smearing a coat on top may not be successful, and is not likely to look too good.
Yes the lens is leaking. I ought to try taking it apart and rebedding it. Not sure there's a downside since I'll have to get it professionally done anyway, if I do nothing or if I screw it up.

Either way, I REALLY want to stop the leaks.
 
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