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Old 14-12-2009, 18:51   #1
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Rubber Gaskets for Bedding Deck Hardware ?

Our '77 Ericson has rubber gaskets under a SS plate at the chain plates. I would guess that the rubber gaskets were original equipment.

I am wondering if cutting neoprene or rubber material to put under all deck fittings might be better than using caulk ?


-Sven
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Old 14-12-2009, 19:01   #2
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My experience is no. I have seen this on a lot of boats of that era. The rubber gets compressed and hardens and then starts to leak. Of course rubbers have improved a bit since the 70's

Will be interesting to here what others have to say

Wayne Canning, AMS
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Old 14-12-2009, 19:36   #3
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I use 3M 5200
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Old 14-12-2009, 19:47   #4
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I like polysulfides rather than polyurethanes for bedding, but if the fitting is bolted on my favorite is butyl rubber. It stays flexible and watertight and is easy to work with. Plus you can remove the fitting without taking the deck with it.
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Old 14-12-2009, 19:54   #5
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Neoprene rubber is the best gasketing and bedding material for deck hardware. It will outlast any bedding compound and the only reason for using those is that it is quicker (but messier).

I get my material on Amazon, search it for "neoprene rubber". I use both 1/8" and 1/16" thick rubber. You need to tighten the fasteners so that it really compresses, like to 50% of original thickness. Cut the holes for the fasteners a bit bigger.
Here's all the tools needed and a simple gasket I made recently:

ciao!
Nick.
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Old 15-12-2009, 00:56   #6
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Sheesh Nick, the admiral really lets you do that to the cabin sole???
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Old 15-12-2009, 04:52   #7
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I used to use 5200 but I've seen the light.

If you're waterproofing something that's through-bolted all you need is a sealant, specifically:
3M 101
Sika 291

A lot of people use 3M 5200 for this purpose which is not recommended - 5200 is an Adhesive/Sealant which actually ends up being far less mastic than the sealants. Since the mechanical fasteners are taking the load as it were, you just need something gooey to keep the water out (and they stay gooey).

Not to mention it's a real bugger to have to remove 5200 should the need arise.

I imagine certain types of rubber will work as well but the problem is that it's pretty hard to get a spec sheet for rubber. So you don't know how it'll age, take sun and respond to salt water. I tend to use rubber for more delicate applications like instruments - basically anything you don't want to remove with a chisel and hammer.
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Old 15-12-2009, 05:17   #8
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Speaking as someone who has been replacing/rebedding a sh....er, 'boatload' of deck hardware over the past several months...some of which came with rubber gaskets, I can unequivocally say that they are crap. What usually happens is as the fitting is tightened the rubber compresses and the gasket contorts, many times squeezing out in places. So you either don't snug down the fitting so that when the rubber decomposes...which it will...the fitting is left flopping in the breeze, or you snug down the fitting which distorts the rubber gasket from its proper place, rendering it worse than useless. And combining a rubber gasket with a bedding compound just makes it worse to get a proper seating.

Toss the rubber gaskets and just bed the hardware in a proper bedding compound like 3M 5200 for 'permanent' fittings (i.e. throughhulls, cleats, etc.) and marine silicone for 'temporary' hardware that may need to be removed at some point such as lights, fans, antenna/electrical deck mounts, etc.)

Oh, and most importantly, use proper backing for fittings and hardware, and not just washers or a piece of a paint stick for cripes sake.
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Old 15-12-2009, 05:32   #9
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Quote:
Originally Posted by s/v Jedi View Post

ciao!
Nick.
Here's a prime example of a leak waiting to happen around those 4 holes, particularly on a boat deck which is usually uneven and/or a rough antislip texture. I guarantee that by the time that this gasket is installed either; the deck is being compressed beyond what it should be, the gasket is compressed to the extent that it is oozing out the sides, and/or it is not tight enough (or conversely too tight), and the rubber doesn't have a proper seal around the holes. Not to mention that sun, salt, and rubber don't mix well.
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Old 15-12-2009, 05:54   #10
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Nick,
I'd like to try this on my boat. What is the tool you use to cut the holes?
Z.

Quote:
Originally Posted by s/v Jedi View Post
Neoprene rubber is the best gasketing and bedding material for deck hardware. It will outlast any bedding compound and the only reason for using those is that it is quicker (but messier).

I get my material on Amazon, search it for "neoprene rubber". I use both 1/8" and 1/16" thick rubber. You need to tighten the fasteners so that it really compresses, like to 50% of original thickness. Cut the holes for the fasteners a bit bigger.
Here's all the tools needed and a simple gasket I made recently:

ciao!
Nick.
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Old 15-12-2009, 07:28   #11
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@donradcliffe: that piece of plywood has a single coat of epoxy on one side to make it a bit harder and it's the most often used "tool" aboard. Most of the scratches you see, incl. the circular ones are from a hot knife used for cutting Sunbrella.

@muskoka: the 3M 101 is a polysulphate and thus a true bedding compound. I don't think the Sika is, but LifeCaulk from Boatlife is the same as 101 and comes in handy tubes for smaller projects. It keeps good forever. When it cures, it becomes a rubber much like the neoprene sheet material I show in the photo, but not of the same quality so it will fail sooner.
Neoprene gaskets are another step up but, as I'll explain further below, not for every situation.
Neoprene rubber will not harden like you describe... that sounds like natural rubber to me!

@Not Sure: I am confident that you never made a good neoprene gasket for mounting something yourself, yet you post like you know it all. The experience you have is with some rubber gaskets that came with stuff you bought and you think it's the same as what I showed. You should first try something yourself and find out if it's any good or not. Some points:

- It must be neoprene rubber. Neoprene has excellent UV and salt resistance; much much more than any cured bedding compound. Put some 101 or if you like 5200 on a piece of cardboard. Stick a small piece of the material I described next to it and put it in the sun and salt spray and water etc. You know that the neoprene will outlast the rest by an enormous factor.

- When you use a liquid bedding compound that cures to a rubber, it will take the shape of whatever you put it between. When you use sheet material, it's shape is fixed. This means that both the surface you mount on and the flange of the hardware must be straight and fit together within close tolerance. If it doesn't, it will never be optimal but a bedding compound will at least seal it while a neoprene gasket won't.
If you bolt something to deck you should sand away any anti-slip pattern or material in that spot, no matter what you use for bedding.
For things like bolting railings and stanchions to deck, or chainplates to the hull, the neoprene material rules as long as you keep the above in mind. Never use sheet material to bed something weak, like plastic.

- There are hundreds of types of neoprene rubber and only a few will do. The density is the most important factor, the thickness second. Don't think the stuff of a wet suit which is more like a neoprene foam, not a solid rubber. You need something like a 60D Durometer density. This is much harder than you think and the best comparison is the rubber of the flexible mounts of your engine. It's easily available, like here: Amazon.com: neoprene rubber sheet

- The hole pattern must allow you to tighten it without deforming the flange of the object you fasten. You have to do this in a pattern like the head on an engine block and the flange must be strong enough. The deck should not compress at all which means that a cored deck needs it's core removed and replaced with solid epoxy in that spot. If you can't tighten the fasteners without deforming the deck or flange, it won't work no matter what bedding you use, plus, a stanchion or railing will not be secure nor safe. Normally, the fasteners must be tensioned to 20% of their breaking strength. There are tables that will translate this to a setting for your torque wrench. This is crucial for stuff like chainplates and stanchions.
The holes in the neoprene gasket will squeeze into the thread of the fastener when the gasket compresses, but you still need to seal the head of the fasteners. Apply a little 101 or lifecaulk on the shaft of the fastener just under the head.

- You have to choose the right thickness. Always go for 1/16" thick first and cut it 1/16" smaller than the flange. If it bulges out in one spot there's something wrong. If it bulges out the same all around, cut it a bit smaller after checking that the torque on the fasteners is right.

- And you should really really never ever use the silicone as you state. Never use silicone for bedding deck hardware! Really, NotSure, this just shows that you do not have the level of experience with this as I (and many others on this forum) have with this. There's two ways to deal with that: the hard way which will result in expensive lessons, or give some credit to the members who live their life aboard a boat full time for a long time, like me, and give our suggestions a try before condemning them. If you use silicone, you will never be able to remove it all and can never do a small fiberglass repair in that area, nor paint it etc. etc. It will forever be contaminated. Search this forum for hundreds of posts on the subject. Use rubber, either the neoprene sheet or one that cures like 101 or lifecaulk.

- There's nothing magic about 101 or lifecaulk. It cures to a rubber and that rubber is weaker than neoprene sheet. Just cure a bit and check it out.

@Ziggy: it's a deluxe version of a hole-punch. The kit on the photo is from Sailrite but any good hardware store should have it. It has a spring-loaded center pin and it works like a dream. You get every size punch with it that you'll ever need.

cheers,
Nick.
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Old 15-12-2009, 08:01   #12
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Nick, thanks for an excellent informative post,this is what these forums are great for.Its always amusing when some know all comes on and says that something that has been working for years wont work.
Steve.
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Old 15-12-2009, 08:03   #13
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Nick,

That was the kind of answer I was looking for.

I would have guessed that an 1/8th or 3/16ths thickness would have been a better starting point. Is a 16th really thick enough to bulge like an o-ring around fasteners ? Do you make the holes the same size as the fitting or one size smaller ?

How to cut it was going to be my next question but you beat me to it.

Thanks (and to everyone else who answered too).



-Sven
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Old 15-12-2009, 08:25   #14
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Nick,

I don't know if they are any better than Amazon, but have you ever priced your neoprene with Mcmaster Carr?
McMaster-Carr
Just about any flavor you like and ship quickly and cheaply. They also have a section that describes properties and uses of different rubbers, although I like this one better:
Selecting Rubber Compounds - Natural Rubber, Neoprene, Nitrile, EPDM, Silicone, Hypalon, SBR, Viton

Mike
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Old 15-12-2009, 08:36   #15
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Quote:
Originally Posted by s/v Jedi View Post

@muskoka: the 3M 101 is a polysulphate and thus a true bedding compound. I don't think the Sika is, but LifeCaulk from Boatlife is the same as 101 and comes in handy tubes for smaller projects. It keeps good forever. When it cures, it becomes a rubber much like the neoprene sheet material I show in the photo, but not of the same quality so it will fail sooner.
Neoprene gaskets are another step up but, as I'll explain further below, not for every situation.
Neoprene rubber will not harden like you describe... that sounds like natural rubber to me!

@Not Sure: I am confident that you never made a good neoprene gasket for mounting something yourself, yet you post like you know it all. The experience you have is with some rubber gaskets that came with stuff you bought and you think it's the same as what I showed. You should first try something yourself and find out if it's any good or not. Some points:

- It must be neoprene rubber. Neoprene has excellent UV and salt resistance; much much more than any cured bedding compound. Put some 101 or if you like 5200 on a piece of cardboard. Stick a small piece of the material I described next to it and put it in the sun and salt spray and water etc. You know that the neoprene will outlast the rest by an enormous factor.

- When you use a liquid bedding compound that cures to a rubber, it will take the shape of whatever you put it between. When you use sheet material, it's shape is fixed. This means that both the surface you mount on and the flange of the hardware must be straight and fit together within close tolerance. If it doesn't, it will never be optimal but a bedding compound will at least seal it while a neoprene gasket won't.
If you bolt something to deck you should sand away any anti-slip pattern or material in that spot, no matter what you use for bedding.
For things like bolting railings and stanchions to deck, or chainplates to the hull, the neoprene material rules as long as you keep the above in mind. Never use sheet material to bed something weak, like plastic.

- There are hundreds of types of neoprene rubber and only a few will do. The density is the most important factor, the thickness second. Don't think the stuff of a wet suit which is more like a neoprene foam, not a solid rubber. You need something like a 60D Durometer density. This is much harder than you think and the best comparison is the rubber of the flexible mounts of your engine. It's easily available, like here: Amazon.com: neoprene rubber sheet
I have experimented with this and also seen numerous manufacturers here in the US use this method and have issues. My buddy Brian was a surveyor. I would help him out often when he needed a hand. Nearly every boat we came across with gaskets had severe deck moisture. I suspect that as the neoprene compresses over time people do not re-tourque..

I have tried punching the holes smaller, larger, multiple torques etc. and still experienced failures. I have also experimented with different thicknesses and densities as well as silicone rubber gasketing and Nitrile (Buna N) with 55-65 durometer ratings.

None of these prevented water ingress as well as a slight countersunk bevel around the bolt holes and a polysulfide, polyurethane or butyl rubber. My favorite is butyl rubber but it is more labor intensive and requires more finesse than does a product like 3M 101..

While gaskets can work they are much more difficult to get a long lasting seal out of, in my actual experience, applied to bedding boat hardware.

I tried the ultimate test of a gasket. I actually made a set of gaskets for the lifting davits of my dinghy which reside 100% below water on my RIB. It leaked within the first week, not a big leak, but a leak none-the-less. This was even after sealing the bolt heads.

I then re-did it with 3M 101, countersunk holes, and the tighten once method. It is now going on 8 years old bone dry and these fittings are below water..




I think I may experiemnt this spring with butyl tape below the water and see what happens. I have used it for years above deck but not below water. I think eight years of below water use confirms that the tighten once/countersink method works very, very well and is easy to do..
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