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Old 09-03-2013, 22:33   #1
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Best sealant for hull deck joint

We have a pretty interesting situation. The westsail 32 has a hull to deck joint that looks like this:


Its a common problem that eventually the dolphinte (sp?) that was put into this joint when the boats were built would dry out and a leak could develop. Most owners just caulk the outside of the caprails to prevent water from ever making it to the joint but we opted to pull ours off and recaulk the joint as best we can.

The joint isn't so neat as it is in the construction diagram. The gap between the outer hull and the inner turn is variable in width.


It is also pretty wide.


We're trying to figure out what to re-caulk this with for the long haul. We can get some caulk up under the actual overlap as it isn't perfect. But that wide gap concerns me. We need a very very flexible adhesive caulk that won't dry out.

I'm considering using 4200 but wanted to here other thoughts on comparable polysulfides like Lifecaulk. And then there is always butyl which I imagine has less chance of drying out and hardening, but will it stay where we put it?

Advice from the hivemind greatly appreciated.
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Old 09-03-2013, 22:43   #2
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Re: Best sealant for hull deck joint

use 5200
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Old 09-03-2013, 22:46   #3
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Re: Best sealant for hull deck joint

Quote:
Originally Posted by donradcliffe View Post
use 5200
That is what we're currently digging out of the joint...
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Old 09-03-2013, 23:03   #4
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Re: Best sealant for hull deck joint

Quote:
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That is what we're currently digging out of the joint...
Now that was funny......true, but funny
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Old 10-03-2013, 00:59   #5
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Re: Best sealant for hull deck joint

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Now that was funny......true, but funny
lol
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Old 10-03-2013, 01:26   #6
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Re: Best sealant for hull deck joint

I'd vote for butyl, lots of it. We've never had a single leak on anything using butyl including the full hull/deck joint.
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Old 10-03-2013, 01:52   #7
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Advice from the hivemind greatly appreciated.[/QUOTE]

Hi,
No joke, widen gap to 3/8" about, fill dust and moisture free gap with non drying automotive mastic. Replace rail.
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Old 10-03-2013, 05:02   #8
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Re: Best sealant for hull deck joint

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I'd vote for butyl, lots of it. We've never had a single leak on anything using butyl including the full hull/deck joint.
I wouldn't use 5200 but I do second butyl.
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Old 10-03-2013, 05:24   #9
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Re: Best sealant for hull deck joint

I 3rd the use of butyl on that joint.

Whats there looks to be bondo
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Old 10-03-2013, 06:59   #10
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Re: Best sealant for hull deck joint

Quote:
Originally Posted by mikefossl View Post
I'd vote for butyl, lots of it. We've never had a single leak on anything using butyl including the full hull/deck joint.
I would agree 100% if this was between the two flanges but this is a band-aid, after the initial construction fix filling an exterior gap.

Butyl requires compression, as CS did at the factory, to work best. Our boat has been around the world, in her 34 years with a butyl hull/deck seal, and never had a single leak BUT this was done at the factory on a very wide overlapping deck/hull joint.

Perhaps the cap rail could provide the compression needed but I suspect it would be a lot of work to make it compress correctly with just a screwed in teak cap rail.. Not saying it won't work but just urging caution..

For a marine sealant I tend to like Sikaflex 291 as it is a little thinner than 3M and tends to "settle out" into nooks and crannies better. A trowel can also be used to "force" it into any open spaces... The most important thing in any job like this is to clean, clean, clean, prep, prep, prep.........

Personally I might just glass the whole joint with some fiberglass tape and epoxy....
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Old 10-03-2013, 07:02   #11
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Re: Best sealant for hull deck joint

A few years ago I asked the senior technical engineer at Dow Chemical this question. He said in his opinion there were two good solutions (and many bad ones).

1. if the joint flexed (a lot), or had differing rates of thermal expansion (as glass curtain walls on sky rises do), he recommended the industrial glazing two part poly-sulfides. He said these were technically massively superior (both in initial adhesion/elasticity, and in life span before losing elasticity) to all the one part products (polyurethane and poly-sulfides). He said for someone without commercial accounts that Tremco's distributors, one of the big distributors like McMasters were the easiest place to buy these products.


2. If the joint did not flex much (and he thought a toerail joint like this would be in this category) the best solution was to pack the gap with fiberglass and epoxy, and then to glass over the joint (again with fiberglass and epoxy). It was preferable to glass over both the inside and outside of the joint, but an excellent job on just the outside would be satisfactory. He considered this the only 'permanent' solution.

He was extremely dismissive of the technical properties of all the one part products (including 5200) available (and they do make a few). Said that they were obviously a bit more work to use but there were much better technical alternatives in two part products.
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Old 10-03-2013, 08:03   #12
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Re: Best sealant for hull deck joint

we used 5200
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Old 10-03-2013, 08:16   #13
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Re: Best sealant for hull deck joint

Just as a quick follow-up . . . you probably already know this, but whatever you do you want to clean out the old sealant right back to bare glass as well as you can. That should certainly be doable on the outside the joint (inside and outside the hull), but may be difficult inside the joint. A careful job with a router with a very thin bit is one way to get that (or at least enough of the joint) clean/back to bare glass.

The glass/epoxy approach especially demands bare glass. The epoxy will likely not bond well to old sealant. So, if you can't get the inside of the joint clean, then a hybrid approach might make sense - squirt two part polysulfide inside the joint, let it cure, and then glass over the joint outside and inside the hull where you can get the glass clean.
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Old 10-03-2013, 08:39   #14
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Re: Best sealant for hull deck joint

I would not use a soft sealant but rater a structural adhesive. If it were my boat I would use a Methacrylate such as Plexus you can get it from Jamestown Dist. It is more expensive but will bond very well even when you cannot fully clean the surface. This is a very durable material and will last a lone time. I would try to get it in as deep as possible and completely fill the gap between the flange and the hull to the top. I would then bed the wood cap rail in 5200.
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Old 10-03-2013, 08:39   #15
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pirate Re: Best sealant for hull deck joint

I just re-read post #1. This may well fall into the it wasn't broken category. But I guess it is now.
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