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View Poll Results: Which keel joint sealant do you prefer?
Sikaflex 291 3 13.04%
3M 4200 6 26.09%
3M 5200 10 43.48%
Other 2 8.70%
No winner - they all do the job 2 8.70%
Voters: 23. You may not vote on this poll

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Old 22-09-2019, 21:19   #16

Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,304
Re: keel joint sealant - which one?

From Maine Sail:

5200 is a totally over rated product and the biggest scam put forth on the uneducated boating public I've ever seen. The ONLY place for 5200 or any product like it is a hull / deck joint and even there I'd use Sikaflex over 5200 because it remains more flexible than 5200. Even a hull to deck joint will flex too much for 5200 over the long term.

The product I'd use would be Sikaflex 291 LOT. This product has better flexibility for the expansion / contraction / flex between the lead and fiberglass than does 5200. 5200 is for boatyards who want future repair business or novice boaters who know no differently. I know quite a few of the top quality yards here in Maine use Sikaflex including Lyman Morse & Hinckley and NOT 3M 5200. Sika Flex 291 LOT has a 700% elongation at break while according to 3M 5200 is 350% so 291 LOT is twice as flexible.

Flexible is what you need between a fin keel and a flexible fiberglass hull. The sealant does not need to glue the keel on that's why you have keel bolts! It only needs to adhere to the fiberglass and the lead and be FLEXIBLE.

Nothing and I repeat NOTHING on a boat is a permanent seal. Trust me I had to re-bed my keel that was originally bedded with 5200. Once the keel bolts were loose they jacked my boat up but the keel was still holding on in certain areas even though it was leaking. After letting it hang for a few days they began trying to separate it with oak wedges. No Luck! They actually had to use a sawzall to get my keel off in the end. The problem was when they got about half way through & the weight of the keel literally ripped chunks and delaminated the fiberglass keel stub. They then had to repair that.

The keel on that boat was put back together 10 years ago with Sika Flex 291 LOT NOT 3M 5200 and is still bone dry today. The reason it needed to be re-beded in the first place was because it was not flexible enough & after a few years it began leaking!

Don't believe me here's what 3M has to say..*"Because 5200 is so strong and its primary use is for permanent applications like those in hull-to-deck bonding, 3M introduced 4200, which is about half as strong and is more suitable for general-purpose applications. “If you want to get [the adhesive] off, go with the 4200, says Dewey."*5200 is one of the few products that will NEVER set foot on my boat Sikaflex is more flexible over time and more than strong enough for ANY boat application including a keel joint. Sikaflex 291 is about the same adhesion as 4200 but far more flexible!!

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