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Old 10-04-2021, 20:40   #1
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Geocel (ex Dow Corning) Marine Sealant

Has anyone used Geocel Marine Sealant and knows if it has decent UV resistance? All the litrature Ive found so far only mentions that its good for interior and exterior and makes a good water tight seal.

I need to reseal my chainplates, and I know that Silicone on a boat is evil, but the PO used SCS2000 silicone. Allegedly its UV resistant but has rotted in two and a half years.

For choice I would use butyl tape but I can mechanically fix the chainplate covers to the deck so I'm stuck with another silicone product.

Dow Corning 795 is now branded as Dowsil 795 but as far as I can find not avaliable in NZ.
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Old 11-04-2021, 14:25   #2
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Re: Geocel (ex Dow Corning) Marine Sealant

You don't need a uv resistant sealant. The caulk will be shielded from UV by the chainplate if external or by the cover plate if deck mounted. Polyurethane and Polysulfide have adhesive qualities and should hold down cover plates actually better than sillycone. Use 5200 if you want to be sure the plates will stay down. You can bed the chain plates themselves in butyl which I'd reccomend and the cover plates in whatever. Why can't you screw the cover plates down?? If the screws are stripped, clean out the existing caulk by drilling slightly oversize to be sure they are clean. Fill the screw holes with thickened epoxy using a bit of straw or wire to be sure the epoxy has no voids or you could jam a small bit of hardwood in the hole with the expoxy to give a screw more bite. Drill and tap for machine machine screws or drill for sheet metal screws to hold the plates down.

Dow 795 is sillycone. Granted it's a much better behaved sillycone but still sillycone. I'm not particularly fond of sillycone and looking to do gross bodily harm to the idiot PO's who used sillycone on boats I've bought. Sillycone belongs in Boobs not boats and I'm not even sure about that.

Use Butyl tape, polysulfide (LifeCaulk), or Polyurethane (3M 5200/4200 and others) to bed the chain plates. 5200 isn't a permanent sealant but you'd think it was if you ever have to remove something bedded with it. Probably acceptable for chainplates but wouldn't use it on anything that I had even the slightest inkling that I might need to R&R in the future.

Used GeoCel to seal some trim, etc on my house and wasn't impressed, wished I'd used Life Caulk.
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Old 11-04-2021, 19:41   #3
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Re: Geocel (ex Dow Corning) Marine Sealant

Geocel has held up well for us around the windows on the house (5-10 years) and for installing watertight bulkheads in our kayaks. Used it on our deck at the chainplates last summer - too early to report on its service life yet (less than a year) in that application.
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Old 11-04-2021, 19:51   #4
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Re: Geocel (ex Dow Corning) Marine Sealant

Thanks for tge replies.

I always understood that once youve used silicone it gets into the substrate and neithrr polyeurathane nor polysulphide will stick to it, or am i misinformed?

I cant screw the covers down because the outside end sits under the toe rail so there is no way to get a fixing in there.
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