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Old 20-09-2015, 04:35   #1
JMK
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Options for water in deck's balsa core

The survey on the boat we recently purchased found some water in several areas of the balsa cored deck. Our last boat had similar issues, but the core was Airex so it wasn't quite as significant. Any other options for repair besides cutting off the top of the deck, digging out the rotten core material and reglassing with Airex or another impermeable core material? I don't think I'm up to the challenge of cutting out the coring from underneath because of access issues and the mess of glassing upside down in a space your also trying to live in.
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Old 21-09-2015, 21:38   #2
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Re: Options for water in deck's balsa core

Is the core wet? Assuming it is, one way is to stop the leaks. Drill some small holes from below to allow draining. If you keep your boat dry, the overhead will be the warmest and will help dry out the balsa. Or use a dehumidifier.
After it's dry, tape over the holes and drill out over the balsa where the leaks were and fill with epoxy mixed with high density filler to the top of the drill holes. Remove the tape below and refinish as you please. This won't please the purist, but makes a permanent repair.
I would guess the leaks were from screws holding railings and other topside fixtures. When I drive screws in wood or cored fiberglass, I first drill well oversized holes and fill with epoxy and high density filler. After the cure, I drill a proper sized hole. Then when I drive the screw, I squirt, with a syringe, a small amount of epoxy in the hole to lube and hold the screw. That way the screw is encased in epoxy. If water seeps down the threads, it can't get into the core. The screw doesn't loosen with time.
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Old 22-09-2015, 03:59   #3
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Re: Options for water in deck's balsa core

Thanks for the advice. The source of the water incursion is probably a combination of leaking deck hardware and leaking ports with the water migrating down to the deck. I've started at the top by beginning to replace all of the ports so I can properly seal them. Re-bedding deck hardware would be next. I also use the method of over-drilling, epoxy fill and re-drilling for mounting hardware. I'll give your technique a try to see how it works. I can monitor the results with moisture reading comparisons before and after.

Cheers,
J.M.
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Old 22-09-2015, 04:53   #4
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Re: Options for water in deck's balsa core

I have the same issue due to teak. I started with epoxy, but I just got some gflex, and am going to do the rest with that. Allegedly it can flex more then standard epoxy can, and bonds to wet wood better.
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Old 23-09-2015, 03:39   #5
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Re: Options for water in deck's balsa core

Our last boat had teak decks over a deck with an Airex core. I got tired of chasing leaks from the deck so we took off the teak and sealed the deck. I know a lot of people love their teak decks, but I sure don't miss them.
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Old 23-09-2015, 05:09   #6
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Re: Options for water in deck's balsa core

Plenty of threads on this (well worth a search).

Long story short, you either do the job properly (yikes!) or stop the leaks, repair / replace core in critical areas, live with it....and hope the next buyer does not notice :-)

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Old 23-09-2015, 05:51   #7
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Re: Options for water in deck's balsa core

Have dealt with this a number of times over the years, including several boats with serious wet core problems I sold when I was a broker.

First and most important and urgent, stop the leaks so the problem doesn't get worse. If you have to pull deck fittings and tape over the holes until you can do a full repair then do it, now!

Second, don't seal in moisture. If you don't fully dry the core before reinstalling the hardware, rebidding ports, etc then you are creating a long term problem that will come back to bite you in the butt in the future.

If you don't mind the cosmetic impact or plan to repaint the decks then it is by far easier to cut in from the top than underneath.
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Old 23-09-2015, 06:07   #8
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Re: Options for water in deck's balsa core

We had to do this job on our Bristol 24, and while I won't say it was fun it wasn't' the worst job we've ever had to do on a boat. We replaced the wet balsa by cutting off the deck fiberglass from above (very carefully with a circular saw blade set very shallow so that we could put the cut away parts back). We replaced the balsa with more end grain balsa, coated well with epoxy, then glassed the original deck pieces back in place. Lastly we removed every piece of deck hardware, drilled out the screw and bolt holes well oversized, filled with thickened epoxy and then redrilled so that any future leaks couldn't get to the balsa again. It was a good repair, we had solid decks and didn't have to worry about it anymore.
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Old 23-09-2015, 06:26   #9
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Re: Options for water in deck's balsa core

If the soft deck is by deck fittings such as this Genoa track or through deck chain plates you do NOT have to cut the deck.

I removed my Genoa track and then used a dental pick to remove the rotted wood from around the bolt holes. Once I got to good wood, the hole was vacuumed, sealed on the bottom using painters tape and then slowly filled with resin. Once cured, the resin was re-drilled for the screws.


Variations of this process should work for any soft spots related to anything mounted to the boat, provided the soft spot can be cleared of wet wood.

The good news is that by preserving the inner and outer skins, the repair is more aesthetically pleasing and a whole lot easier.
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Old 23-09-2015, 06:59   #10
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Re: Options for water in deck's balsa core

I've done this for other people several times in the past year. Usually where you think there is a little rot, there is a lot of rot.

I've been working on a 1977 POS skiff boat the wealthy owner (ironically a mechanical engineer that manufactures things with plywood) wanted to fix up cosmetically despite my urgings from the beginnings to ditch the project. He was attached to the boat which he said he had "rebuilt" mechanically with his sons, which amounted to rewiring the console and powder coating two cockpit lights. The deck was a little "boingy" in multiple areas and the owner just shrugged it off saying it was "functional." So I drilled a 3/8 inch hole into the deck and showed him the wood seemed deteriorated (but was not obviously wet.)

On three further occasions I expressed doubts about the deck, stringers and fuel tank. Fast forward $2000 worth of body work etc... After taking off the console and large deck inspection plate underneath it, the fuel filler hose was completely deteriorated at the hose clamps to the fuel tank (when the tank was filled fuel would leak out into the foam the tank was surrounded by) and had to be replaced which required cutting into the deck. Despite the boat being stored inside a building for four months, the wood in the core was SOAKING wet and so mushy you could take it out with a spoon. I say wood, because they must have run out of plywood the week they built the boat and there were three inch wide boards of wood between the fiberglass skins instead of plywood. The project is now on hold as he will definitely end up with $8000 into a $5000 boat if he is lucky.

The point of this long story is that the most common "boat killer" by far is rotted core material if you don't count general neglected maintenance. Pet peeve: on sailboats, "boy racer" types frequently festoon their boats with improperly bedded gadgets and gauges which are useless to the average cruiser and cause extensive damage from water infiltration. When a sailboat has a liner, these areas are very difficult to detect and often missed by the surveyor who is not obliged to drill or do other destructive testing.

Four years ago I thought my Cal 34 had a nice tight deck. It didn't. In several small areas there were obvious signs that someone had repaired the deck using the technique Lepke mentioned above. When I read on Compass Marine's website the exquisitely detailed article on how to bed deck hardware, I stripped my deck and found lots of rot. The areas that were repaired with the "drill a bunch of holes and inject epoxy" method were hardly affected- still delaminated and ripped off the ceiling as easily as the rest of the wood. Besides not being effective, the numerous drill holes are impossible to disguise on a nonskid surface.

Don't put screws in with epoxy, use butyl tape and don't forget to campher the holes.

On a Cal, the interior skin of the fiberglass-wood-fiberglass laminate is very thin, not enough to support any weight which almost requires doing the job from inside unless it is done in small areas. Having done it from the inside once, the next time I would do it from the outside in small areas with something other than plywood as core.

I'm working on an affordable substitute for the expensive "rot proof" core materials and "rot prone" organics currently available. If you are interested PM me.
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Old 23-09-2015, 08:49   #11
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Re: Options for water in deck's balsa core

Here is a funny article written by a well known marine surveyor about core material:

Structural Issues : Core Materials
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Old 24-09-2015, 02:29   #12
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Re: Options for water in deck's balsa core

Actually that was a GREAT article. Thanks for the everyone's input. I think the plan moving forward will be to cut out the areas from the top and use balsa that I'll epoxy before replacing the skin. This will be in addition to re-bedding hardware and replacing the ports that were already on my list. Not easy, but doable.

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Old 24-09-2015, 05:14   #13
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Re: Options for water in deck's balsa core

Just drilling oversize and removing a little bit of balsa around the hole is almost pointless.
I just rebuilt a pair of cockpit locker lids, 3 bolts hold the hinges on each side at the back of the lid.
The lids are about 40" x 18", the balsa core was absolutely soaked from side to side and front to back. The actual rot was only about an inch or so around the holes. The balsa was like a sponge, you could squeeze water out of it.
So what started as a "simple" repair ended with me removing the skins from the back sides of both lids, epoxying in new core then re-glassing.
12 - 1/8" diameter holes turned into a week project and a couple hundred $ in supplies.
And here silly me thought I was just going to over drill and fill those holes!
You will not believe how far back you will have to go to find dry wood.
Wasn't a difficult job, messy and time consuming, still have bits of dried balsa blowing around my driveway, but on the skill meter I'd rate it about a 3 out of 10 for difficulty.
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Old 24-09-2015, 10:34   #14
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Re: Options for water in deck's balsa core

Quote:
Originally Posted by skipmac View Post
...First and most important and urgent, stop the leaks...
don't seal in moisture...
This.

Regarding how to effect a proper repair, small repairs are almost always easier to do from the underside, where nonskid and exterior finishes can remain untouched. Also the inner skin is usually much thinner than the outer, and so the repair patch requires fewer layers. The deck's underside is usually finished with some kind of headliner material that hides the fiberglass skin. Repairs here will not be seen, and so may not even need fairing and finishing.

If core damage is extensive, you bought the wrong boat.
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