Wet balsa core repair options?

[prof_mariner]

I am considering a boat (Morgan 32) built in 1979. The hull is solid fiberglass laminate and I'm assuming the deck is balsa cored fiberglass. A recent survey found high moisture levels in areas of the deck and cabin. Ordinarily I would walk away from a boat with this issue but the boat is in otherwise good condition and the price is attractive. So I am considering taking this on as a project. I've purchased a moisture meter and plan on surveying the deck thoroughly to map where the wet areas are and how extensive the damage is.

So my question is, what options are there for repairing / replacing the core? Besides cutting the deck, pealing off the laminate and replacing the core, are there any alternative methods I should consider?

[hobopacket]

Nope. Tear it off. Replace. Regales to seal. Honestly if you have worked with glass before know how to use a grinder. It’s not a big deal. Just takes lots of patience and hard work. Good may and resin/hardener can get expensive. Then you have to paint. If the price is attractive enough and you are handy. Could be a good deal. Hard to find an old boat with a cored deck without some core rot.

[Terra Nova]

If you must ignore common sense, first thoroughly and professionally correct the initial cause of the water ingress. Then consider replacing the wet/rotted core sections from inside as: a) it will allow the exterior to remain undamaged/unmolested and watertight, and b) there will be less finish work and less glassing, as the inner skin is almost certainly a fraction the thickness of the external skin, the repairs to which should not be so obvious to potential future owners.

[skipmac]

Depends on how bad and how far it spreads. I had a number of spots on my decks, mainly under stanchion bases, around chain plates (largest +/- 3" diameter) and a fairly large area (around 8" X 20") in the cockpit floor that had leaked and in places rotted the core.

I removed the fittings, gouged out the bad core, sealed the deck side and left the cabin side open for a few weeks to dry. In the larger, worse spots, I drilled small ventilation holes from below around the edges of the wet spot and taped a vacuum hose to the main hole and let it run for a while. Some that were very wet I sealed the bottom and filled with acetone from the top.

When totally dry I filled the smaller spots with thickened epoxy, the large one with a mix of cloth and resin.

[Tia Bu]

I've dealt with a good bit of it over the years. It's not that difficult to repair, and it really does scare away buyers. (Surveyors love to impress people with their little hammers.) So you can probably get a good deal on the boat, and if you're willing to do the work yourself and do it well, you should have a great boat at a good value.

[Sailorman Ed]

what options are there for repairing / replacing the core?

I have had a fair bit of experience on this. And mostly worked from the top as it was so much easier. I carefully tapped to find the wet vs solid areas, marked them, cut out the skin and then ripped out the wet balsa. I was brutal about this. It ranged from dust to wet but solid. I removed EVERYTHING soft. If it was solid but just damp, I let it dry completely.
I then cut and fitted Divynicel foam, gave it a coating of epoxy, mixed a slurry of epoxy and 1/4 glass fibers and bedded the foam into the area in question . I weighted it ( batteries, chunks of lead, bags of sand, cans of paint) to get a good level result. Blending in with the remaining deck was the most difficult part.

This project is not for the faint at heart but I did it all in a marina slip. I was careful of wind direction, kept the docks cleared, cleaned up every night and checked to make sure I was not a nuisance to my dock neighbors.

I bought epoxy in 5 gal pails, had a variety of fillers and mixed only what I could use within the pot life. It was interesting that it did not take much of a hole for water to get in and then migrate longitudinally,

BTW, I finally figured out that I would pump in resin only after emptying my mixing container and it would not harden, saved a lot of cleaning and wasted cured epoxy, even for overnight. I always used 5 pumps so it was easy to remember the next time.

[smurphny]

I re-cored most of the decks on my A35 when I first got her. There really is only one proper way to do the job: Cut away the old FG, lay in new core and feather in new glass. It's a messy job but well worth it in the long run. Also, it is not rocket science and you can usually do a better job than the original lay-up by laying in solid sections under thru-deck fittings and making sure the core is WELL saturated with epoxy. I found the reason for delamination is mostly because water was able to get to balsa. You can saturate the balsa, spaces, etc. more carefully than they did on a production line. Any questions, feel free to ask.

[prof_mariner]

Thanks for the helpful feedback.

When I first looked at the boat I was told that both the decks and hull were solid glass. It wasn't until I got the results of the survey that I learned that the decks are (likely) cored and had a moisture issue. I bought a moisture meter and will go back and check the deck more thoroughly once the weather dries up. My decision to buy or not will likely be based on how much wet core I find.

Yes, I would prefer to do the repairs from below decks, but this model has a hard liner and I'm not sure that is possible. If not, I'll have to do it from topside. If I do the repair from topside, I'll probably try to preserve the original "skin" as best as I can so I can re-use it. Any recommendations on how to feather the edges of the old skin so it's not too ugly?

[Terra Nova]

Originally Posted by prof_mariner

...I'll probably try to preserve the original "skin" as best as I can so I can re-use it...

Fuggetaboutit.

[smurphny]

Working with gravity seemed the only logical way to go for a number of reasons. The edges need to be feathered at 12:1 as relates to thickness of the glass. Glass needs to be laid in LARGEST piece first. Saving cutouts was a nice thought but impractical. Some pieces may come out whole but most will be semi-adhered, requiring more drastic removal. Chisels, sharp edges, whatever works will get it removed quickest. You will also need to leave a couple of inches at edges to feather which requires using something to get in under there to dig it out. Long recipe saw blades work. Long drill bits, as I say, whatever works.

[sailor_ed]

My Gulfstar 41 (center cockpit) had large portions of the deck with wet core. Two sections were about 18 inches by four feet. Also the cockpit sole, the area under the mizzen etc. The old Bristol yard (which built Bristol Yachts) did the repair which is holding up well 20 years later. They proceeded as follows 1) a circular saw was used to cut around each area and the deck pried up from the core which was 1/2 inch thick. 2) the wet core was removed and the area prepared for glass ingredients. 3) the polyester glass work was done all in one go as follows: wet mat was placed in the void so that the edges lapped up around the edges. Then 3/8 inch balsa core cut to closely fit in the available space was inserted. Finally another layer of mat with the edges lapped up. The deck piece was then fit into place with the 2 layers of mat filling the kerf left by the saw cut. The mat and balsa were dry fitted before the resin work. 3) after the resin kicked the mat, which was now standing proud around the deck piece, was ground down flush to the deck. 4) the exposed mat edges were finished with gel coat. Where there was a seam between non skid a layer of gel coat was used to make a similar cosmetic seam on the other side of the boat. The final deck looks almost as if it had been designed that way.

To sum up the 2 layers of mat sealed in the new core which was enough thinner so that when the original deck piece was replaced it lay flush with the original deck with the mat filling the saw cut. All grinding marks were hidden with gel coat stripes. Very neat and "original" looking.

[prof_mariner]

@sailor_ed - Wow, that is a very clever way of handling this issue. I bet this method would benefit from a simple vacuum bag to pull everything together.

[sailor_ed]

I'd be a little afraid what the bagging would do to the mat sticking up in the kerf. Even after grinding there was not much of a seam to gel coat.

I will add that the gel coat "seams" stand slightly proud of the nonskid which distinguishes them from the normal gaps molded between non skid deck areas.

[Time2Go]

Originally Posted by prof_mariner

I am considering a boat (Morgan 32) built in 1979. The hull is solid fiberglass laminate and I'm assuming the deck is balsa cored fiberglass. A recent survey found high moisture levels in areas of the deck and cabin. Ordinarily I would walk away from a boat with this issue but the boat is in otherwise good condition and the price is attractive. So I am considering taking this on as a project. I've purchased a moisture meter and plan on surveying the deck thoroughly to map where the wet areas are and how extensive the damage is.

So my question is, what options are there for repairing / replacing the core? Besides cutting the deck, pealing off the laminate and replacing the core, are there any alternative methods I should consider?

Check out “Sail Life” on YouTube
The gent just did a complete recore
You can get a good idea of what your in for
Cheers
Neil

[prof_mariner]

Originally Posted by sailor_ed

I'd be a little afraid what the bagging would do to the mat sticking up in the kerf. Even after grinding there was not much of a seam to gel coat.

I will add that the gel coat "seams" stand slightly proud of the nonskid which distinguishes them from the normal gaps molded between non skid deck areas.

Good point. So how did they maintain pressure on the deck laminate while the epoxy was curing? Using weights?