Sounding the core, some mush, some delamination .. question

[Jasper Windvane]

Did some sounding at my bad core spot. This is in the area where the hand/grab rail bolts came through the cabin roof deck. Near to the holes, mush. A the mush goes out a few inches. Then,, not so mush. In fact, when I drilled a look see hole last spring, the core was looking good, but maybe a little wet. As I get away from the hand/grab/bolt holes, I feel there is good core, maybe a bit wet, and some delamination.
My question: I don't want to open up more deck than necessary. If I open up the deck to reveal the bad mush core but the core/deck further away is good, maybe a bit wet, and some delamination .. what do I do? Let it air out? Therefore dry? Once dryed, do I inject epoxy from drill holes into the delamination area? How long does it take for the moisture to get out? Boat is not inside, and this work won't start until warmer weather. I'm trying to keep the deck opening cut to a minimum. But I don't want to go to all kinds of trouble and not do the job right.

If would seem logical that as the moisture spreads out from the center of the bolt holes, where the core became mush, that there is delamination because of this moisture..

What have you more experienced core mushers found?

Thanks..

[Tim]

Experience shows that core damage is typically larger in area and more significant than you first expect. You'll get better results if you open a larger, rather than smaller, area; it doesn't pay to confine yourself to an artificially small opening during repairs. It's a big job that you only want to do once, and it's not really any more work to open (and then repair) a larger area than a small one, once you've reached a point where this sort of major repair is required.

That said, you don't want to cut sections of deck that contain sound and well-bonded core, though a small amount of this at the perimeter of any cut is unavoidable. So take your time in the testing and exploratory stage so you know what you're getting into.

If you can't get a good enough idea of the extent of the repair area from sounding or other indications, and you're unsure how large a section to remove in order to access and replace the core, then drill some exploratory holes through the top skin with a relatively large bit (1/2")--one that will allow you to really look inside and see not only the core's condition, but also how well it is bonded to the skins. When you get clean, bright, dry core that is well bonded to both skins, you know you've reached the outer reaches of your repair area, and can mark and cut a section of deck accordingly. Exploratory holes are easy to repair.

If you're doing anything larger than a very confined spot repair, then plan on opening the deck and removing all areas containing core that is wet, mushy, or moist, or areas that are debonded from one or both skins. Injection is for the smallest spot debonding repairs only; once you've committed to any sort of more destructive and significant repair, be sure you get it all, and remove any and all remotely suspect core material.

For clarity, note that delamination technically refers to the separation of layers within a laminate, such as your fiberglass deck skin. Separation of the skin as a unit from the core material is typically referred to as debonding.

[Jasper Windvane]

Thanks,, Tim.. always get the good advice here.. So far, my job is just at the planning, getting the tools together, etc stage. But.. soon. I hope.