Poll! Keel re-bedding product recommendations!

[rwthomas1]

Hello All!
If you don't know by now I have removed the keel on my E38 and done a bit of restoration on the keel bolts. Now its pretty much ready to go back in and the boatyard and I have done plenty of research on what to use to re-bed the keel and have come up with plenty of options and opinions. So here is a poll on what to use. Both the boatyard and myself have been recommended to use 3M 5200, 3M 4200, Sikaflex, Epoxy, Polysulfide, etc. etc.

Some members here have recommended different products for different reasons, all of them good but not without questions regarding suitability. Thanks to all that recommended options, I do appreciate the input.

The other interesting thing is that NO manufacturer specifically states that their product is ideal for bedding a keel. The boatyard thinks this is due to liability issues, they don't want to be responsible for any perceived failure.

The boatyard and I have tentatively settled on using 3M 4200. Why? Its rated for below waterline use, quite strong, remains flexible and can be removed more easily than its "big brother" 5200. So what say the mob? I think there are probably a few products that would work fine but it seemed like a good idea to do a poll.

RT

 

[Cory B]

Epoxy

I think any of them properly applied would probably do.

However, we used epoxy on the recommendation of the yard. After I did a bit of research I found that both Pacific Seacraft and J-Boats both recommend it as well. With two boat manufacturers as disparate as those two both recommending it I figured it was a safe bet. We just hauled the boat this morning, about 2 years after applying the epoxy, and there was zero seam visible.

A note on epoxy though (it may apply to other sealants to a lesser extent as well), you need a certain amount of thickness for it bond properly. In our case, there is about 1/4 epoxy between the keel and the shoe. It was important not to tighten the keel bolts so tight initially that it would squeeze all the epoxy out.

As far as removing the keel again down the road, it lasted 20+ years with crappy sealant, undersized washers, and under-prepared surfaces. I figure we should be good for at least 50 years now... probably longer than me.

I did ask the yard what would happen if we ever needed to drop an epoxied keel, and they said they could (and have) done it with power chisels or somesuch thing. It didn't sound pleasant.

I clicked "Epoxy" for the poll, but now a few minutes older and wiser I probably shouldn't have selected anything at all.

 

[Emerald]

Hi Cory,

I don't want to get the polll off-track, but did you thicken the epoxy with colloidal silica (or something else)?

 

[Cory B]

Thickened Epoxy

I don't want to get the polll off-track, but did you thicken the epoxy with colloidal silica (or something else)?

Yep, it was thickened. I wish I could say with certaintly with what, but I think it was mix of micro-fibers or chopped glass with colloidal silica to a peanutbutter consistency.

I was looking over their shoulders a lot that day, helping where I could.

 

[JohnK]

...The other interesting thing is that NO manufacturer specifically states that their product is ideal for bedding a keel...

Well, not quite - Detco Hull Caulk "2-part, non-sag, putty consistency polysulfide rubber, blended from THIOKOL polymers, for caulking wooden hull seams and for bedding keels"

 

[u079721]

Not so sure anymore

My yard rebedded our 38 using thickened West System Epoxy (which just happened to be located two miles down the road). I liked the idea of having the keel glued on so that the bolts were almost unnecessary.

But in my case the job was finished off by glassing over the seam. And the problem was that every couple of years (or after a particularly tough storm) the glass over the seam would crack in front. Since I would then worry about water intrusion, I would want to get it fixed. Not sure if this is true of all glassed over seams, but it sure was on my 38. Too flexible?

Anyway, I now think that 5200, which is supposed to remain somewhat flexible, might have been a better choice - as long as the seam was not glassed over.

But the adivce above is good - regardless of what you use, be sure the yard doesn't squeeze it all out right away. My joint was allowed to cure for at least a week before the bolts were tightened.

 

[rwthomas1]

JohnK, is Detco the product you used? I have a call in to them requesting more information. I would like to know specifics about adhesive qualities, tensile strengths, etc.

I am not in favor of using epoxy or any other "hard" adhesive to attach two components with different expansion rates. I think that over time this difference in expansion/contraction will cause failure. Just my opinion.... I like the idea of a slightly flexible product far better. MaineSail has indicated that the 3M products, indeed all polyurethanes will harden over time loosing their flexibility. The question is how long? I can't seem to get a good answer for this.

RT

 

[Maine Sail]

Sikaflex !

Having done this job, and seen how 5200 lasts, or doesn't, my vote goes to Sikaflex!!!

 

[JohnK]

JohnK, is Detco the product you used?

Yeah, the Hull Caulk which is thicker than the Deck Caulk. As far as technical details, I looked at the Thiokol data sheets (Thiokol invented polysulfide). The key feature for me is "THIOKOL® Sealants will provide as long as twenty-year service life under normal application conditions, which surpasses that of commonly used polyurethane sealants". Another site that sells 2-part polysulfide with technical data is here. Again, key phrase is "maintains a low modulus of extension even after prolonged exposure to the elements. This prevents adhesive and cohesive failures which often occur when a caulking compound hardens excessively with aging."

 

[Gary Peterson]

On our 1983 381 I am replacing the original Marelon thru hulls with bronze this winter. The marelon fittings were originally bedded with 5200 and it is still pliable and very difficult to break out the fittings. I have had to use a jig saw to cut out the marelon thru hulls in pieces. The 5200 is still rubbery though.

 

[Rocinante33]

This is a link to an article by Don Casey. To quote from it,
" Polysulfide is the most versatile of marine sealants. It is a synthetic rubber with excellent adhesive characteristics, and you can use it for almost everything. As a bedding compound it allows for movements associated with stress and temperature change, yet maintains the integrity of the seal by gripping tenaciously to both surfaces. It is also an excellent caulking compound since it can be sanded after it cures and it takes paint well."

http://www.boatus.com/boattech/casey/35.htm

 

[Gary Peterson]

If integrety of the joint is paramount, I would, and did vote for 5200.
The tensile strength of 5200 (polyurethane) is 700 psi, elongation is 1350%.
Thiokol (polysulfide) has a tensile strength of 80 psi and an elongation of 550 %.

 

[treilley]

So are we gluing or sealing the keel? Aren't the bolts there to hold the keel on. Why does it need such a strong adhesive? That is going to be a pain to remove and it seems to be a widely accepted truth now that you should be dropping the keel on these boats for inspection every 20 years or so.

My boat is 23 and I have no idea what it is sealed/glued with but whoever did it also taped with glass and epoxy and faired. The hull looks like an encapsulated keel and the bolts look good in the bilge although I know that corrosion could be evident in the bolt's recesses. I will likely drop mine in 2 years for inspection and rebedding.