Join Date: Jan 2003
Location: Maine Coast
Thanked 295 Times in 228 Posts
Rep Power: 17
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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