Re-bedding Chainplates - advice needed

[Beersmith]

I had new stainless chainplates made for my boat and am ready to install them. I plan on using Sikaflex 291 or 4200 to fill the gap around the chainplate and the caprail/deck, and then using butyl tape to seal the cover plate.

Based on some research, I got the chainplates polished to a mirror finish, supposedly the reason is to aid in avoiding crevice corrosion where the chainplate is sealed up.

HOWEVER, this is where I am confused. Any sealant recommends that the surface be scuffed up for adhesion, and this goes against the idea of the polished finish.

What gives? Should I scuff up the metal before sealing it to help adhesion of the sealant, or leave it the mirror/polished finish and risk the sealant not adhering properly?

this is what happens when you do too much research conflicting steps, both seemingly necessary though

[a64pilot]

I would leave them polished, but re-bed every other year or so unless you have a way to inspect to know when the bedding begins to leak. I don't, so I have to go with re-bedding on a schedule.
I bet you will get different answers

[sparrowhawk1]

I would keep them polished and use butyl tape. I've had every type of caulking fail on me except the butyl, it stays soft and it adheres well

[Beersmith]

Originally Posted by sparrowhawk1

I would keep them polished and use butyl tape. I've had every type of caulking fail on me except the butyl, it stays soft and it adheres well

hehe, I was originally planning on using only butyl; but it seems that most people recommend filling the gap between the chainplate and the deck with a sealant that can fill up the gap like Sika or 4200. then I'll see a comment like yours and completely doubt my chosen path

I'm a big believer in the butyl and have rebedded pretty much everything with it. I just want to get the chainplates as well bedded as possible.

[sparrowhawk1]

If your chain plates are flush with your deck and you want to do the best job possible make a dam out of playdough or something similar about 2 inch gap around the chain plate. Put some butyl rubber around the chain plate and fill in the space with an epoxy filler like Marine Tex. This will raise the opening around your chain plate greatly minimizing the amount of water trying to penetrate

[sparrowhawk1]

Here's a photo of how I did mine looks like it only is about an inch and a quarter wide or a quarter inch bigger than the plate that sits on top. And notice the butyl rubber squishes out a little bit. Edit. You can also make a wooden frame and stick it to the deck with the Play Doh or even butyl rubber. It will make the job lot faster if you have several to do

[Beersmith]

Originally Posted by sparrowhawk1

Here's a photo of how I did mine looks like it only is about an inch and a quarter wide or a quarter inch bigger than the plate that sits on top. And notice the butyl rubber squishes out a little bit

Attachment 82031

cool idea! Mine are on the teak caprail though, here is a pic:

[Suijin]

Originally Posted by Beersmith

I had new stainless chainplates made for my boat and am ready to install them. I plan on using Sikaflex 291 or 4200 to fill the gap around the chainplate and the caprail/deck, and then using butyl tape to seal the cover plate.

Based on some research, I got the chainplates polished to a mirror finish, supposedly the reason is to aid in avoiding crevice corrosion where the chainplate is sealed up.

HOWEVER, this is where I am confused. Any sealant recommends that the surface be scuffed up for adhesion, and this goes against the idea of the polished finish.

What gives? Should I scuff up the metal before sealing it to help adhesion of the sealant, or leave it the mirror/polished finish and risk the sealant not adhering properly?

this is what happens when you do too much research conflicting steps, both seemingly necessary though

Don't confuse best practices for "adhesives" with "sealants". For adhesives, it's a good idea to prepare the surface for good adhesion either through chemical or mechanical means, but sealants do not always require that treatment to be effective, particularly when they are serving fundamentally as a gasket. While people give silicon a bad name on boats, it's an excellent sealant, in part because it has relatively poor adhesive properties (and so can be easily renewed/replaced).

For your chain plates DO NOT rough them up. I'd go with the Sikaflex and then butyl under the plate. I *think* 291 has a lower tensile strength than 4200, making it a more agreeable solution should you ever need to replace the bedding.

DO build up a plinth of some sort, if possible, @ 1/2" off the deck to keep the bedded hardware out of standing water.

[sparrowhawk1]

Something I just thought of. if your gap around the chain plate is real deep the other type of caulking could be for keeping it from flexing too much. With the butyl rubber keeping it sealed

[Beersmith]

Originally Posted by a64pilot

I would leave them polished, but re-bed every other year or so unless you have a way to inspect to know when the bedding begins to leak. I don't, so I have to go with re-bedding on a schedule.
I bet you will get different answers

Originally Posted by Suijin

Don't confuse best practices for "adhesives" with "sealants". For adhesives, it's a good idea to prepare the surface for good adhesion either through chemical or mechanical means, but sealants do not always require that treatment to be effective, particularly when they are serving fundamentally as a gasket. While people give silicon a bad name on boats, it's an excellent sealant, in part because it has relatively poor adhesive properties (and so can be easily renewed/replaced).

For your chain plates DO NOT rough them up. I'd go with the Sikaflex and then butyl under the plate. I *think* 291 has a lower tensile strength than 4200, making it a more agreeable solution should you ever need to replace the bedding.

DO build up a plinth of some sort, if possible, @ 1/2" off the deck to keep the bedded hardware out of standing water.

Originally Posted by sparrowhawk1

Something I just thought of. if your gap around the chain plate is real deep the other type of caulking could be for keeping it from flexing too much. With the butyl rubber keeping it sealed

thanks for the advice