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Old 08-01-2023, 23:46   #1
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Spongy spot on deck

Hi all

We purchased a 2008 Lagoon 380 S2, and despite not appearing in our survey, we have found a spongy spot on the rear starboard deck. There is also evidence of (old) water ingress in the owner's (starboard aft) cabin roof lining and some of the ply walls. It appears likely the water has come in from the hatch or possibly the leg of the hardtop bimini. I am addressing both those things as a priority to prevent any further leaks.

I have a couple of questions I would love some input on if anyone else had had a similar issue:

1) I understand the hull below the waterline is solid fibreglass, does anyone know what the deck is - i.e. is it balsa core or something synthetic?

2) It appears the lining in the cabin is a single moulded piece. I am thinking I would need to cut it in order to get to the core of the affected deck. Does this sound feasible? I am thinking I could then rejoin it with some kind of trim to tidy it when finished.

3) If anyone has had to fix this type of issue I'd love your advice, and if you have any pictures that would be awesome.

This is not a job I would attempt myself as I am not experienced enough, but would love to know what advice / assistance I can give to the fibreglasser when we do the repairs.

Thanks
Trevor
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Old 08-01-2023, 23:59   #2
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Re: Spongy spot on deck

Not sure but most likely balsa coring.

Once you find the leak and seal it of, the repair is pretty straight forward.

If you can get at it from below behind a headliner, it's very much a DIY kind of project. Just make sure to tarp everything so splatters don't get on anything.
- Check out west system epoxy (even if you use another brand). They have excellent directions on how to do a lot of fiberglass work.

If you have to go in from above where it will be visible, still not rocket science but a good fiberglass guy and make it near impossible to see where the repair was done. This is where there is a bit of artistry to color match (white is not white) and get the edges to blend with the surrounding fiberglass.
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Old 09-01-2023, 01:44   #3
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Re: Spongy spot on deck

Deck its balsa core sandwich construction, i would find a good professional and repair it from below, above it will be difficult to maintain the appearance of the gelcoat unless you find a gelcoat guru.
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Old 09-01-2023, 03:26   #4
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Re: Spongy spot on deck

Thanks for the responses. I suspected the deck was balsa core - do you know if the hull is also balsa core? From what I am reading it appears the hull below the waterline is solid (monolithic) but my concern is whether the water damage might extend to the hull above the waterline. I am having a surveyor on board on the weekend and hopefully he can determine how far the water damage has extended. Fingers crossed it is just on the deck!

Any hints on what I can look for to determine where the damage ends and the core is solid? I have tapped the hull pretty much all over and it sounds "solid" other than the patch on the deck which is obviously damaged and sounds hollow. Is there something the surveyor can use to determine this non-destructively? I am probably being paranoid, but since the original survey found nothing I want to make sure this one is comprehensive
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Old 09-01-2023, 04:11   #5
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Re: Spongy spot on deck

Moisture meter.

Above the waterline? I don't think so, but tell the surveyor to measure the topsides to.
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Old 09-01-2023, 04:14   #6
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Re: Spongy spot on deck

Thermal camera can found wet rot balsa spots to.
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Old 09-01-2023, 15:25   #7
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Re: Spongy spot on deck

Thanks Neil, I'll make sure the surveyor is very thorough this time!

I don't suppose you (or anyone else) has removed the liner in one of the cabins? I will need to do that to repair any rotted core, but it all seems like one big piece which would be a nightmare. I was wondering if it is removable or if I'll have to cut it out...
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Old 14-01-2023, 21:48   #8
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Re: Spongy spot on deck

Just an update. The surveyor went over things yesterday and there is definitely an issue on the back deck, but it appears to be limited to an area of around 1.5 square metres. He is going to get the repairs effected at his cost as he acknowledged that this should have been picked up in the survey. The issue is that the cabin liner is one solid piece attached to the hull, so they won't be able to get in behind it - may have to cut it, do the repairs then put the liner back together with some kind of trim. For anyone interested I'll post some pictures once it's done.
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Old 14-01-2023, 22:18   #9
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Re: Spongy spot on deck

That's a pretty large area. Not unusual but certainly repairable.

Standup kind of surveyor if he's paying for the repairs. Most surveys come with a big disclaimer that they aren't responsible if they miss things.

Assuming the repairs work out without problem, come back and let us know who the surveyor is. I would trust him over a surveyor who claims never to miss anything.
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Old 14-01-2023, 22:50   #10
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Re: Spongy spot on deck

A little info on Moisture Meters, Thermal Cameras and Percussive Soundings may be in order ....
Moisture Meter Mythology and Flir thermal imager

PS. Your Lagoon 380 decks, superstructure and topsides from midships aft are of FRP balsa cored sandwich construction.
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Old 15-01-2023, 02:48   #11
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Re: Spongy spot on deck

Quote:
Originally Posted by valhalla360 View Post
That's a pretty large area. Not unusual but certainly repairable.

Standup kind of surveyor if he's paying for the repairs. Most surveys come with a big disclaimer that they aren't responsible if they miss things.

Assuming the repairs work out without problem, come back and let us know who the surveyor is. I would trust him over a surveyor who claims never to miss anything.
Yes, I have to say he has been very co-operative in this whole process. He also flew from Townsville to Cairns on Saturday at his own expense. I'll let you know how the repairs go - it is booked in for late February / early March.
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Old 15-01-2023, 02:53   #12
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Re: Spongy spot on deck

Quote:
Originally Posted by boatpoker View Post
A little info on Moisture Meters, Thermal Cameras and Percussive Soundings may be in order ....
Moisture Meter Mythology and Flir thermal imager

PS. Your Lagoon 380 decks, superstructure and topsides from midships aft are of FRP balsa cored sandwich construction.
Thanks for that info. The surveyor did say he didn't totally trust the water meter, but it did seem to support the opinion he got from tapping the deck.

Regarding the FRP balsa cored sandwich construction, would I be right in assuming that water ingress would have caused the balsa to rot?
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Old 15-01-2023, 04:02   #13
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Re: Spongy spot on deck

Quote:
Originally Posted by Trevor Doble View Post
Thanks for that info. The surveyor did say he didn't totally trust the water meter, but it did seem to support the opinion he got from tapping the deck.

Regarding the FRP balsa cored sandwich construction, would I be right in assuming that water ingress would have caused the balsa to rot?
Yeah, water ingress , see if there is any piece of hardware close to the spongy area in question, , cleat, hard top tubes etc,,, deep cracks in the gelcoat or something suspicious..
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Old 15-01-2023, 07:22   #14
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Re: Spongy spot on deck

Quote:
Originally Posted by Trevor Doble View Post
Thanks for that info. The surveyor did say he didn't totally trust the water meter, but it did seem to support the opinion he got from tapping the deck.

Regarding the FRP balsa cored sandwich construction, would I be right in assuming that water ingress would have caused the balsa to rot?
It is possible, depends how long it's been in there. Some surveyors can be pretty accurate with that question depending on their experience levels. Others will require core samples from a hole saw.
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Old 15-01-2023, 07:49   #15
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Re: Spongy spot on deck

Yes, I repaired rotten deck core on my sailboat. See my "Dismasted, June 2016" album for photos. It is easier from the deck down rather than up. I cut the deck off with a multipurpose tool, laid down end grain balsa pieces with lots of resin and filler, and covered with multiple layers of woven glass and epoxy. Once you cut the deck, you can determine the extent of the rot, and keep cutting until you find clean deck.

With careful painting, it could be nearly indistinguishable.
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