Fiberglass Repair - fill with epoxy or replace core?

[RicTrim]

When I bought the boat several years ago, the fwd hatch hinges were loose in the fiberglass hinge pads. As an inexperienced captain, I got a West System repair pack from WM and fixed at the problem. In addition, I went ahead and drilled the holes through into the cabin and put bolts/nuts on. Also, a couple years ago, I put an anchor light on top of the mast and re-wired the steaming light. I drilled a new hole for the wiring thru the cabin top and only used silicone to "bed" the wires. The original wires (beside the mast tabernackle) I cut off at the deck and squirted some lifecaulk into that hole.

We recently removed the hatch to paint the inside of it, and decided to repair the hinge pads correctly. I got a quart of resin, hardner, some coidal silica, and figured a couple hour or so job.

The admiral went to work with the dremel (I was too chicken), and we have discovered that we are the owners of rotted core and wet core. Overall, the area adjacent to the hatch up towards the tabernackle and down towards the port on the port side of the boat - we have removed about 1 square foot of the gelcoat - we sucked out the rotted core and some of the really soaked but not quite rotted core.

The question now becomes - how big of an area can be done with just epoxy and when is it necessary to replace that core with new end-cored balsa? My guess is that I need core. According to Don Casey's book - the core needs to be epoxyed - then put in - then the deck epoyed to that....

Any suggestions? One good thing - where we have opened it up - the other core at the edge of where we dug out the other stuff has dried where the air and the heat can get to it...

I guess I'm asking for a source for the end-grain balsa core material... And does it come 1/2" thick? I believe that is what is in there now.

Thanks,
Ric

 

[JoshGray]

Not too difficult a repair

Ric,

Your core is most likely 3/8" end-grain balsa. I have done this very repair although in a different place(s) on my O'Day 22 (pictures can be found on the linked website). I dug out the rotted and wet core until I found dry material. I know that Casey suggests you could dry out core that is just wet and that it will be fine. Although the spores that produce the rot may still be there, without oxygen they won't make any progress (assuming you seal it up with epoxy appropriately). You should clean the lower fiberglass "skin" very well and wash it down with some acetone, then create a pattern for your new core material (easy enough to find 3/8" scored & scrimmed balsa on the net), paint slightly thickened epoxy (colloidal silica) onto the lower skin, install new core with the scrimmed side down and the scored side up to conform to the deck's curvature, fill in all the creases and holes with more thickened epoxy. Then, if the top skin is still usable you can epoxy that to the top, weigh it down and let it cure. Otherwise, you can begin laying up a new fiberglass top skin.

Jim is right about large batches of epoxy, especially thickened ones and especially when using the fast hardener... they will kick very, very quickly and will be very, very hot. The trick is to not allow the mixture to get too deep; use a very broad mixing cup or bowl.

And, obviously, reinstall any hardware with the preferred "potting" method discussed in Casey's books, that way if the fittings leak they won't wet your core.

Cheers!