Sealing the Bitts with Cotton?

[Idon84]

I was reading over my building manual, specificly having to do with sealing up the bitts, and found something that I have a question about.

The manual mentions to uses Calking Cotton packed tightly around the bitts under deck level and then using White Silicone to seal at deck level. It also mentions that you should re-pack & silicone yearly to keep the best seal possible.

I've never thought about doing this before and was going to use Sika 291 LOT before reading this. I'm guessing that the movement of the bitts could possibly make it impossible to seal 100% over a period of time? Is cotton a better idea than 291 LOT for this or just more work?

One builder friend of mine says to just pour in epoxy to perminantly seal it up. When I say that the bitts would no longer be removeable, he gives me a look and askes when would I ever plan to remove the bitts in the future. I guess he has a point there. Perminant is attractive but repairability is important too.

Thoughts, opinions?

[Paulus]

Bitt? Underdeck? I'm confused.

[Tallystick]

Are bitts wooden posts on the deck? 4200 seems like a reasonable choice.

[Idon84]

Yes, bitts are the vertical posts that allow for dock line ect. to be attached to. They also support the for/aft movement of the bowsprit. They take quite some shock loads I would assume hence my question. Everwhere else in the manual states using bedding compound, but for this specific part they want cotton, and I'm curious as to why.

[mitiempo]

The cotton I guess will fill the gap and hold the sealant. I certainly wouldn't use silicone though. New silicone doesn't even stick to old silicone.

As far as it needing resealing often goes it depends. All sealant has a elongation factor. If there is very little thickness of sealant, say 1/16", even if it elongated to double you only have 1/8 before it breaks free. The thicker the sealant within reason the more it will stretch before a gap is created. Sika 291 would be a good choice, or butyl which never sets and has probably the best elongation of all sealants.

[earlylight]

I agree with mitiempo. I would use butyl wpecifically because of its elongation capability and because it never hardens. Good luck!

[Tallystick]

Mcmaster-Carr carries butyl caulk in a range of colors. http://www.mcmaster.com/#butyl-caulk/=gb2l5c

[mitiempo]

Not sure what type of butyl McMaster Carr carries but here's a link to what may be the best for marine purposes. http://www.pbase.com/mainecruising/butyl_tape

[Tallystick]

The McMaster variety is not tape. It comes in a standard caulking tube.

[mitiempo]

Does it have the same stretch and stickiness as the link I posted?

I have used butyl on deck fittings and my boat (CS27) had all hardware sealed with butyl when built, including the hull/deck joint. None I have seen or used would be able to be used in a caulking tube as it is not soft enough. It sounds like a different product.

If you read the link I posted you will see that there are many products called butyl that do not have the properties of butyl, have lots of fillers, etc.

[Tallystick]

I used the McMaster butyl for bedding the fixed portlights on my boat. It comes out of the tube soft, and cures to a very flexible rubbery material that adheres well to fiberglass and metal. It doesn't stay sticky after it cures.

[mitiempo]

Butyl doesn't cure and stays soft and sticky. The butyl used on my deck fittings and hull/deck joint is the same consistency today as it was originally (35 years ago) and the same consistency as the new butyl I use.

[Hirilondë]

I don't like butyl for anything under serious load. I am always afraid that because it never cures it may be squeezed out from load pressures and then leak when the load is relaxed. I have a bronze bit and used Sikaflex 291. It is a moderate adhesive, stays pliable but not overly soft and therefore compresses little.

[Tallystick]

That means the butyl was already cured. It's an elastomer, so the properties vary depending on how much cross-linking occurs. Curing is the cross-linking process that controls the properties of the elastomer. A butyl elastomer that has less cross-linking will stay soft and sticky, a bit more cross-linking and you lose the stickiness, but it's still a very flexible resilient material. Without any cross-linking there won't be any elasticity. To say that butyl doesn't cure is totally wrong.

[Idon84]

Thanks all for your suggestions. I think the main purpose for the cotton was to build up an area where the beading compound is to be. Thick beading compound doesn't have as much elasticity which is why, I believe, cotton was used to diminish the gaps so a good seal could happen.

Thanks again,

Bryon

[mitiempo]

That means the butyl was already cured. It's an elastomer, so the properties vary depending on how much cross-linking occurs. Curing is the cross-linking process that controls the properties of the elastomer. A butyl elastomer that has less cross-linking will stay soft and sticky, a bit more cross-linking and you lose the stickiness, but it's still a very flexible resilient material. Without any cross-linking there won't be any elasticity. To say that butyl doesn't cure is totally wrong.

The butyl that I can access from my hull/deck joint as well as the butyl that was exposed when I replaced my forward hatch was still as pliable and sticky as the new butyl I am using - after 35 years. One advantage of butyl besides its elongation is that it doesn't cure or harden.

[Tallystick]

What you're not getting is that there are different kinds of butyl rubber. The butyl you used was already cured when you bought it. Uncured butyl is not a polymer. The curing process i.e. what percent cross-linked the polymer is, determines the durometer and maximum elongation of the rubber. "Cured" is when the cross-linking finishes, but depending on the formulation, "cured" can be a wide range of % cross-linked. That allows the polymer engineer/manufacturer to tailor the properties depending on the application. Like you're saying, once the butyl cures (finishes cross-linking) it is stable and won't cure any further.

Not trying to be argumentative here with you, just trying to clear up the confusion. As for which butyl is better for OP's application, I'm not sure. Depends on if he wants to use a lower or higher durometer of rubber. The optimum durometer likely depends on how much movement the part will experience. The rubber needs to be soft enough to elongate sufficiently, but have sufficient spring back to maintain the seal once the load is released as Hirlonde pointed out.

[mitiempo]

Here's an interesting link that describes the best type of butyl for a marine application, as well as the types not to use.
See post #8
http://forums.sbo.sailboatowners.com/sh ... p?t=138169

[Paulus]

Yes, bitts are the vertical posts that allow for dock line ect. to be attached to. They also support the for/aft movement of the bowsprit. They take quite some shock loads I would assume hence my question. Everwhere else in the manual states using bedding compound, but for this specific part they want cotton, and I'm curious as to why.

Oh, I see.. On my boat I call them Samson Posts....


I have not yet examined how they are sealed through the deck - they do extend all the way down and sit on the hull where they are tabbed and glassed.