Isolating the core

[vanguard64]

I am getting ready to install padeyes on my cabin top for jacklines. I will be drilling through balsa core. I have always potted the holes with epoxy to prevent water intrusion into the core. But recently, I have started to wonder what happens if a crack develops in the interface between the upper skin and epoxy plug when the fitting goes through stress. Would water then seep between the upper skin and the plug of epoxy and into the core. Maybe I am reading too much into this but I wonder if this has been looked at. The other option would be to properly bed the fasteners and hardware using Bed-it tape after creating a chamfered hole. How would this compare in the long run?

[atomvoyager]

Since you are going to properly bed the fitting in bed-it butyl either way then in the long run sealing the hole in epoxy is best even if a crack developed. But that sounds like a theoretical problem that won't happen if done well. Far a 1/4" fastener I drill thru with 1/4 bit then drill thru top skin with 3/8 or 7/16 and use a bent pick to pull out core with a vacuum going back about 1/2" under the deck all around then tape the bottom and inject epoxy thickened to say mustard consistency with a syringe then redrill at 17/64 and countersink the hole slightly to allow the butyl space to work. If you mix the epoxy too thick the bond may not be as strong.

[vanguard64]

I am locating my two Wichard padeyes on the coach roof. These take three 5/16 machine bolts each. I have a sheet of 1/4 inch G10 to make the backing plates.
I have 2 questions related to installation.
1. When adding the thickened epoxy to isolate the bolt holes, I foresee the mixture seeping between the headliner and the inner skin despite applying tape to the hole on the inside. Any special technique to prevent this short of cutting the headliner to gain access to the inner skin surface?
2. The headliner has a concave shape following the curvature of the coach roof. This creates a slight gap between the backing plate and the liner. Should I apply epoxy to the backing plate and sandwich that in to eliminate the gap?

[atomvoyager]

You'll have to determine how much gap you have between liner and the fiberglass deck or coach roof. Best not to have any air gap between liner and deck. If the gap is small then you can inject thickened epoxy up from below to fill it. If more than around 5/8" gap then consider to cut out the liner. Say you have a 4 x 4 backing plate then cut the same size hole in liner, install the fitting and backing plate and make a removable cover board of 6 x 6 and screw it on from below. The curvature along a pad eye backing plate is minor so you can fill it with sealant during assembly or if you prefer bed it in thickened epoxy and let it harden before installing fasteners.

[vanguard64]

I just finished using your technique for isolating the core for the padeye bolt holes and it went very well. There was no gap between the headliner and inner skin and the core was in pristine shape. Great peace of mind when done.
Thanks again.