Watertight seal on thru-bolt deck hardware??? - Page 2 - SailNet Community

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Old 09-14-2009
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I agree with Maine Sail. Overdrill or better yet don't overdrill and rout out core with a Dremel router bit on a flexdrive. Then fill with thickened epoxy before drilling correct size hole. Most often I drill smaller hole and tap for the fastener. I use butyl tape (grey) and bevel the hole. But I take issue with sealing the inside of the hole or backing plate. If the seal depends on the backing plate or sealed nut & washer belowdeck you've already failed in my opinion. If water were to get past the deck fitting you want to know about it quickly. If the backing plate or nut/washer is bedded the water has no place to go except into the core if it can find a way. Maine Sail didn't give a link to his excellent how-to site so I will - I haven't found a better way than this: Sealing Deck Penetrations to Prevent Core Rot Photo Gallery by Maine Sailing at pbase.com
Re-Bedding Hardware Photo Gallery by Maine Sailing at pbase.com
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Old 09-14-2009
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Originally Posted by Valiente View Post
I use a combination of the grey butyl tape (I agree....it's still the best choice) and 4200. I epoxy the holes to insure isolation from the core, then drill through the "donut" and then bed with butyl and coat the "interior" threads with 4200. I also run a fine bead of 4200 along the perimeter of the backing plate...I don't use fender washers if I can avoid them.

It's not a really good idea to seal the inside or backing plate side even with a potted deck core. If your core is not sealed it becomes a very bad idea.

Most all of these bolts are stainless and if the deck side develops a leak but the backing plate side is sealed and not leaking; 1) you won't know you have a leak so that you can fix it. 2) The entrapped water around the bolt can eventually cause crevice corrosion and you will also not see it until it is too late and the bolt fails.

You really only want to seal the deck side. If the fitting leaks you want to know about it to avoid future problems..
-Maine Sail / CS-36T

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Old 09-14-2009
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Originally Posted by SiXeVeN View Post
Where can you find butyl tape? I have been to several local places with no luck. A search on Defender's website was a negative.
I got 2 rolls from The Original RV Wholesalers - RV Sales, RV Parts, Ohio RV Dealers RV Sales Florida RV Dealers. They don't sell the stuff I bought anymore but they sell something in a nice plastic case for quite a bit more. Also something called tacky tape that may be the same thing. But if you search for butyl on their site you will get a bunch of stuff.

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