@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.