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I have two questions about rebedding parts on the deck and was hoping those with more experience than I wouldn't mind chiming in here. There's a ton of threads on this topic, but an understanding of the terminology and basic steps are often assumed.

Potting a hole - is this basically pouring unthickened resin in the hole to seal it from any type of possible water penetration? If yes, do you generally drill the hole larger to allow for the thickness of the cured epoxy?

Countersinking - a process that seems to be highly recommended. From what I understand, it's simply taking a countersink bit and grinding away a very slight bevel around the surface of the hole. Do you do this even if there's a plate between the bolt head and the fibrglass (i.e. Chainplate)?

Thanks all.

Carl
 

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MaineSail has an excellent, detailed post on this (sorry, don't know link).

Actually, potting is filling a slightly enlarged hole with thickened epoxy to seal the core from water penetration. Some of the core should be removed beyond the hole diameter to better seal the core and to give the epoxy a larger area to grip to.

Yes, you countersink even with a plate. The countersink isn't for a screw head to go into, it is to provide a ring around the hole that will contain sealant and act as a gasket. So you should put bevels around the screw holes beneath any hardware, such as chain plates, deck organizers, etc.
 

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Carl, you have the right idea, good luck.
 

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I have two questions about rebedding parts on the deck and was hoping those with more experience than I wouldn't mind chiming in here. There's a ton of threads on this topic, but an understanding of the terminology and basic steps are often assumed.

Potting a hole - is this basically pouring unthickened resin in the hole to seal it from any type of possible water penetration? If yes, do you generally drill the hole larger to allow for the thickness of the cured epoxy?
No, potting a hole is a bit more than that. It is removing the core from the area around the fastener hole, and then coating the void with unthickened epoxy, to coat the fiberglass and core material, and then filling the void with thickened epoxy.

The two reasons for doing this are simple. First, you want to protect the core from water intrusion, which coating it and filling the void with thickened epoxy will do. Second, it will help strengthen the laminate against the compressive forces created when you tighten the bolts down.

Most core materials are not all that high in compressive strength—thickened epoxy has a pretty high compressive strength...so it makes much more sense to have thickened epoxy there to support the loads.

Countersinking - a process that seems to be highly recommended. From what I understand, it's simply taking a countersink bit and grinding away a very slight bevel around the surface of the hole. Do you do this even if there's a plate between the bolt head and the fibrglass (i.e. Chainplate)?

Thanks all.

Carl
Yes, since the void created by the countersinking will allow the sealant to form a natural "o-ring" and help create a long lasting, flexible and durable seal.

BTW, here is Maine Sail's website page on sealing the core.
 

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MaineSail has an excellent, detailed post on this (sorry, don't know link).

Actually, potting is filling a slightly enlarged hole with thickened epoxy to seal the core from water penetration. Some of the core should be removed beyond the hole diameter to better seal the core and to give the epoxy a larger area to grip to.

Yes, you countersink even with a plate. The countersink isn't for a screw head to go into, it is to provide a ring around the hole that will contain sealant and act as a gasket. So you should put bevels around the screw holes beneath any hardware, such as chain plates, deck organizers, etc.
I would've posted this up but you got it before me :)
 

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Do you do this even if there's a plate between the bolt head and the fibrglass (i.e. Chainplate)?
Yes because the seal is not the head of the bolt but rather the shank of the bolt and the underside of the plate. By creating a chamfer/bevel it forces sealant around the bolts shank which prevents moisture intrusion. Sealing the head between the plate and bolt head adds minimal protection though you can still roll an o-ring of butyl to wrap under the head if you'd like or use 3M 101.



Look closely at how the sealant is forced into the threads and against the chamfer/deck on the right and the non-chamfer one or the left has no seal against the bolts shank/threads.



If you really want a great seal chamfer the stainless deck fitting ever so slightly too on the side that faces the bolt head..
 

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Discussion Starter #7
Thanks for the replies. Any suggestions on a tightening process for rebedding parts? I've seen some people hinting about a "2 step tightening process"
 

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Maine Sail,

I've been seeing the recent references to sealing using butyl tape. Your photos don't show this layer. When using butyl tape, is there a sealant layer under the tape or does the use of butyl tape obviate the need for any other sealant?

TIA
 

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Maine Sail,

I've been seeing the recent references to sealing using butyl tape. Your photos don't show this layer. When using butyl tape, is there a sealant layer under the tape or does the use of butyl tape obviate the need for any other sealant?

TIA
I think some confusion comes from it being called "tape." It's more of a strip of gum-like sealant that is pressed on paper backing. You peel it off the backing as a strip, but it can be manipulated like putty. And as you can see from MaineSails pictures, it is very sticky stuff.
 

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What about a countersunk screw in a counter sunk hole? I recently installed midship cleats, I over drilled and filled the holes with epoxy then laid in Sicaflex 291 before pulling the cleats down to 1mm from the deck using spacers (I put Sicaflex inside the countersunk recesses) after allowing the sealant to cure, removed the spacers and nipped up the nuts.
Should the countersunk recess and the head of the countersunk bolt have a different angle of countersinkedness (is that a word?) to allow some amount of sealant to remain under the bolthead?
Regards
UglyDave
 

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There is little point to putting sealant in the fastener hole in the fitting itself. The area where the sealant is required is between the fitting and the deck, and that is why you're supposed to countersink the top of the fastener hole... since that is where the seal that prevents water from getting into the boat really is.

Also, I would point out that the two-step procedure for allowing the sealant to cure has been debunked. It is very difficult to tighten the fasteners properly without breaking the sealant adhesion them. It is also completely unnecessary if the holes have been countersunk so that the sealant can form a natural "o-ring".

I'd also point out that on high load fittings, like cleats, the two stage cure and tighten process can leave the hardware less than completely tight, since the sealant will resist tightening the bolts as snugly as they should be and lead to premature sealant failure as well as possibly a weaker installation overall--since friction between the deck hardware and the deck caused by fully tightening the through bolts are a considerable factor in the strength of the mounted hardware.
What about a countersunk screw in a counter sunk hole? I recently installed midship cleats, I over drilled and filled the holes with epoxy then laid in Sicaflex 291 before pulling the cleats down to 1mm from the deck using spacers (I put Sicaflex inside the countersunk recesses) after allowing the sealant to cure, removed the spacers and nipped up the nuts.
Should the countersunk recess and the head of the countersunk bolt have a different angle of countersinkedness (is that a word?) to allow some amount of sealant to remain under the bolthead?
Regards
UglyDave
 
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