Repairing large swath of balsa core (J/30)

[patrickkidd]

I am replacing my depth sounder in a 1981 J/30. It looks like the 3/4" balsa core is totally rotted to about 8" below the shown instrument hole and the instrument hole next to it. Balsa above is fine.

My plan is to dig out as much as I can and fill it with strips of 3/4" foam covered in epoxy. I've never done this before. Any tips? Any idea how structurally important this part of the cabin top is? The balsa under the instruments on the other side of the companionway appears to be OK, as indicated by a tap-test.

 

[dlochner]

Important. This helps support the cabin top.

The better more labor intensive and stronger method would be to remove the inner skin and all of the rotted core, then properly recore section.

 

[PaulK]

We found a similar hole around a solar vent on our afterdeck. The missing balsa extended from the opening (which looked a lot like yours) 6" in some directions, to about 18" in others. The vent had been there for something like 18 years, so there was plenty of time for the balsa to rot. Sliding gooped-up foam into the gap between the laminates is not easy because there will be hard ridges of old resin on the two inside surfaces that block the new core (if it is the right thickness) from getting all the way out to the non-rotted sections. We used balsa because it matched the original material and it seems to actually resist wicking any leaks better than foam does. I stuffed as much as we could into the spaces (as much and as far as was possible) and let it set. After that we used a caulking gun with a cartridge filled with an epoxy-microballoon mix to fill in the many gaps. Hardware stores and West Marine sell empty cartridges that you can use for this. It was interesting: we drilled a hole at the far ends of the missing core areas, away from the deck opening, and pumped epoxy into into the spaces until it started coming out the holes. Slapping a tape over the hole holds it in, and we watched to make sure it didn't overflow into the opening on the inside. It took us two batches, pumping the epoxy in from different directions to make sure we filled as much as we could. The deck got pretty warm from the epoxy kicking, so we think we made an effective repair.

 

[JRacer]

The way we fixed that type of problem, although not as extensive, in the J24 was to drill small test holes through the inner skin and into the balsa outward in a radius from the obvious damaged point until we got good and solid wood from the drill bit. That defined the outer edges of the bad area. Once that was known, we cut the inner skin with a Dremel tool and removed it in one piece. We then cleaned it all out, gave it plenty of time to dry if necessary and went back with end grain balsa core. West system epoxy followed by a precut and dry fitted piece of balsa. Then epoxy on top of that, replace the skin that was removed and glass or epoxy to fill the void where the cuts in the skin were made. Paint to cover the repaired area and it's good as new. That is what I would recommend.

 

[dlochner]

The way we fixed that type of problem, although not as extensive, in the J24 was to drill small test holes through the inner skin and into the balsa outward in a radius from the obvious damaged point until we got good and solid wood from the drill bit. That defined the outer edges of the bad area. Once that was known, we cut the inner skin with a Dremel tool and removed it in one piece. We then cleaned it all out, gave it plenty of time to dry if necessary and went back with end grain balsa core. West system epoxy followed by a precut and dry fitted piece of balsa. Then epoxy on top of that, replace the skin that was removed and glass or epoxy to fill the void where the cuts in the skin were made. Paint to cover the repaired area and it's good as new. That is what I would recommend.

 

[PaulK]

This hole looks like it is in the bulkhead/aft end of the cabin trunk. If he removes the inner layer out to good core, replaces all the delaminated/rotted material and then layers on fiberglass, he WILL have to paint or gelcoat the repair on the inside for aesthetic reasons. We did that to repair cabin top delamination under our handrails - two areas about 1' x 8' on each side of the cabin top. It looks fine now, 20-some years later. It just seems a shame to have to add all that work for such a relatively small repair here.

 

[CarlN]

How did you determine that the damage only goes 8" down? I'd drill a few small holes at 10" down and see if you get dry core. If so, this is not a dangerously large rotted area. The best way to fix it is to cut out the inner laminate but it is remarkably hard to make this look good again - and this is a very visible spot in the cabin. It's also not an important structural area like near a chain plates or such.

So if it really is localized I'd probably take the "good enough" way out of digging as much rotted core out as I could and then pouring CPES (or other penetrating epoxy) into the opening and let it soak into the remaining rot. Drill a few more holes so you can see the CPES leak out. Let it harden for a week. Then slip wood, or balsa into the slot and pour more CPES in up to about the last 1/2". It's a good idea to dry fit the wood for size then take it out and paint it with CPES. Let that dry and put it back in before pouring in the CPES. Then fill the last gap with a fiberglass putty that contains microballons that you can smooth for the instrument hole.

And this time, be sure to caulk the instruments.

CPES™ - The Rot Doctor

PES is an excellent wood preservation, rot repair and restoration product. It can be used on any wood in boats, in and around homes, Log Homes and RV's.

www.rotdoctor.com

 

[Jackdaw]

And this time, be sure to caulk the instruments.

The solution to the problem is not caulk, but to seal the exposed core created by any penetrations with a coating of low viscosity epoxy before mounting the fastener (or in this case instrument). Caulk will only last so long before it leaks, and it leaks into a sponge.

 

[DrJudyB]

Personally, I’d “do it right” the first time. If it’s too big an area to fix properly from the edges of the round hole, I’d cut away the inner skin to do the repair. I’d Repair the void with the appropriate density foam or balsa, not rely on penetrating epoxy to fix an area I can’t inspect.

if the OP can thoroughly clean the skins from access at the edges of the hole in the panel, then his approach of sliding foam with thickened epoxy into the void is fine. But if the skins aren’t cleaned of all mold before the epoxy is applied,, the skin will delaminate from the new core, and the repair will fail.

I’ve made core repairs where I cut away an inner skin to replace as small an area as 6” x 6” of rotted balsa core. Yes it’s more work than Injecting resin , but it’s a repair that’s “good as new”, not just “good enough”.

IMO, injecting a epoxy through holes drilled in the skins is a good way to reattach outer skins to dry core, but it’s not a reliable way to repair failed core. There is simply no way to ensure that you’ve done a thorough repair Because you can see the damaged core. You have no way to know if you got all the damage fixed. It’s guesswork and wishful thinking. The only way to know for sure that a core repair is properly done is to open up the area and replace the core, IMO. Or at least inspect the area by endoscope. If you can’t guarantee the repair will hold up, it isn’t wasn’t worth doing that way, IMO

From a cosmetic perspective, I don’t see much difference in the final outcome, if you know what you’re doing. Drilling holes for penetrating epoxy will leave a visible repair unless you’re a professional. so will cutting the inner skin away. Both repairs require fairing and a cosmetic topcoat for the finish...

It helps to have a friend with experience show you how if you’re a newbie.

YMMV,
JudyB

 

[DrJudyB]

The solution to the problem is not caulk, but to seal the exposed core created by any penetrations with a coating of low viscosity epoxy before mounting the fastener (or in this case instrument). Caulk will only last so long before it leaks, and it leaks into a sponge.

I agree, but you don’t need special low viscosity resin. Any epoxy resin will do just fine for sealing the edge of the repair before installing the instrument with sealant.

JudyB

 

[CarlN]

The solution to the problem is not caulk, but to seal the exposed core created by any penetrations with a coating of low viscosity epoxy before mounting the fastener (or in this case instrument). Caulk will only last so long before it leaks, and it leaks into a sponge.

I agree. The caulk's not to protect the core. It will be well sealed now by the epoxy putty. I should have said so. But caulk will keep water from dribbling down the inside of the cabin and cut down on mildew smell from dampness near the instruments. Should last 15+ years - longer than the instruments.

 

[Barnacle Bill]

Since it is a J/30, if you really want to get picky, technically the core material has to be consistent with the materials used in production or you could violate one-design rules. Of course, I have a feeling you aren't going to be so picky. BUT, if in fact it was raced one-design and you were dealing with a section of the hull, especially a large section, then picky you should be.