A "big one" - rotten deck under heater chimney

Geoff W.

Makes Up For It With Enthusiasm
Hi all,

Looks like my first "huge" project of boat ownership is unfolding before me.

A month or two back, I noticed water droplet evidence in the forward starboard bulkhead. Then my girlfriend noticed the books in the bookshelf under the heater were wet. Then, I noticed a stream of water coming in from the chimney - ah ha. I promptly stopped using my diesel heater and covered it up until I could take a better look.

The exterior chimney consisted of a wood block silicon-ed to the deck, and metal plates / guards mounted on the block to protect the chimney stack.

Long story short, everything was siliconed together but the deck block rotted away (and is now destroyed) but worse, the block was covering up an old hole as well as the currrent chimney hole, neither of which were water protected in the slightest and the deck core has completed rotted, if not vaporized completely.

Some pictures are below. I don't know where to start, here - looks like I will probably have to sawzall out the deck and replace the core with some new marine ply, right? How can I gauge the extent of the rot? I'm concerned the bulkhead is getting it too, pic of that at the bottom of the post.

I know worse boats than mine have been restored to better shape, but this is pretty scary stuff. Is it all going to be ok!?



Tin Kicker

Member III
Sorry to hear it.
First off, the sidewall between the windows is solid glass and same with the more vertical bit uphill, so this won't extend far left to right. Second, rot usually doesn't go too far uphill. A little, but usually not far. Your question is more fore-aft, just over the top of the window belt.

Assuming you don't have access to a moisture meter, I'd start off tapping the deck with a plastic hammer to listen for the limits of the dead sound. Being plywood, it won't have as much of a change as when tapping balsa, but there should be a tonal difference.
Go to 2:35 in this video if you've not done this:

Then I'd suggest using a really short sharp chisel (or a hook one) and see if you can dig out the rot before harming the fiberglass. I've had luck cleaning between layers with a drywall router and grinding wheel too. If you can dig enough out, you probably can get away with a filler of epoxy and (shredded mat) glass fibers. If it doesn't go terribly far and you can't feel sponginess, I'd heat the area with some lamps for a couple of days to dry it out as best as possible, taking care not to brown the surface. Then build up the area between and around the holes with the epoxy and matt plug, put it back together, and check it from time to time.

If it is soft to the touch for a good ways and extends so far it really needs more attention, I'd probably try to pull the headliner in the salon and fix it from below so the repair doesn't show. (The headliner would be a bear to staple back in place because they used so many staples.) This much rot would be surprising though.

Christian Williams

E381 - Los Angeles
Blogs Author
Is it all going to be ok!?


First question is, how far into the core is it wet or crumbling? Stick a wire or screwdriver in and probe around.

Now, "reality" (in my opinion): If it's not too bad, just clean it out, dry with a heat gun, and fill the void with thickened epoxy. Might be a role for CPES, if rotted wood needs to be hardened up. "Not too bad" to me means that the deck isn't spongy to step on, and the damage appears confined to the holes area. If the core is wet for a big radius, well, hmmm. You wouldn't be the first to live with a spongy deck area.

Your rebuild of the vent hole will stop the leaks and the cabin will be dry again.

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
The ingress of moisture in a case like this is slow, but relentless. I wonder how many years have gone by? (sigh...)
My SWAG, from repairing a small area of coring that had bee allowing some moisture in for about ten years, is that the damage goes about half a foot in all directions.
Since you would probably prefer not to destroy the top, you need to gain access from below. Once you pull enough staples and roll the headliner back, the color change in the translucent inner layer of glass should be a guide. Then, from inside, drill some quarter inch holes, only thru the inner layer of glass. Do not drill up thru the top layer.
You may find some water dripping out.
Oh yeah, get a waterproof cover over the top before any more rain falls on it! Heavy clear vinyl set into a circle of butyl tape will do, and is easy to remove when needed.
Coring is likely probably /balsa. Our whole cabin top is balsa cored.
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Geoff W.

Makes Up For It With Enthusiasm
I can say for sure right now that the deck itself doesn't feel spongy, isn't creaking, crazed, or any other indicator of bad juju. The core between the holes has completely disintegrated, however, so that's a bit of a gap to be filled.

Being in this one specific spot, there's nearly no foot traffic or slamming around going on, and I imagine the hull doesn't flex here too much given the proximity to the chainplates (at least, that sounds right in my head...) so I guess that's a blessing.

The black in the bulkhead seam / trim makes me concerned, I must admit.

I know deck repairs aren't an uncommon task, though obviously nobody ever hopes to have to deal with it. Glad to hear my first step isn't to start cutting the deck out of the boat. I'll keep the thread updated as I go along.


Innocent Bystander
This won’t be so bad. Dig out the rotten core as far as you can get (and as far as is wet/rotten) with a chisel, screwdriver, oscillating saw with a bimetallic blade, and a vacuum cleaner to slurp out the bits. WIth the right tools this will probably take a half an hour.

Let it dry as best you can, with forced warm air if possible, for a few days.

Use a cheap, small, bristle brush or acid brush to coat the inside of the hole with neat epoxy. Press 1” wide strips of 1/2” foam core that have been dipped into epoxy (just like Burger King’s French Toast sticks dipped in syrup) as deeply into the hole as possible, all the way around. Once you have the stuff this is a quick process, like 15 minutes - just dip and stuff, stuff some more, and move onto the next strip. There will probably be some voids left between the edge of the old balsa core and the edge of the new foam, but that won’t be a big deal.

Put some weight on the top of the repair, a few buckets of water perhaps, let cure for a day or so.

Then re-cut the holes, because some of the foam strips will probably still be hanging out a bit. Then coat the edges of the newly-cut foam with epoxy to seal it, and you should be good to reinstall the hardware.

(I left out the part about taping newspaper or other drop cloth material around EVERYWHERE below and around the hole.)

Geoff W.

Makes Up For It With Enthusiasm
Alright, spent some quality time with allen keys and screwdrivers and hogged out about as far as I could go. Tin Kicker was right, the green lines in my pic below are boundaries of fiberglass, which is helpful in this situation.

Fun fact - if you have a cell phone on hand, you can turn on video camera mode + flash on and have a (limited) endoscope.

I dug out a bunch and it seems to affect at least this far --- the aft-wards measurement is based on how far my 5-6in of large Allen key could reach.

Oddly enough there already didn't seem to BE any core for a few inches going aft. Either it disintegrated or got pulled out previously?


I'll let it dry for a couple days but in the meantime., some filler options proposed by folks in here:
- fiber fill + epoxy
- epoxy + foam strips
- structural putty (friend idea)

I also like the idea of CPES or some sort of rot-slowing penetrating epoxy, but how would I get it so far back in there? Things are on weird angles so I don't think flowing liquids would go anywhere but down.

Another thought - I would like to plug and fill that forward hole, as it's a huge, useless hole in the boat. Maybe I could cut a plywood puck and glass that in, then fair/gelcoat/paint/something over that from the deck side? Or, just re-cover with some sort of metal deck plate. My rail meat would never know it wasn't on purpose.

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
One trick for filling in voids where you want epoxy placed way back where it's difficult to reach is to use a flexible "poker" to push your new "core" replacement all the way back. I have at times used upholstery foam, saturated with epoxy in a tray. Then push it all the way in, and then some more, and then some more - until you have the cavity filled up.
But first reach in with a thin blade with a hook bent into the end to be sure that you have pulled out all the soft balsa and have reached solid coring.
Mask off everywhere within four feet of the work. Blue tape and thin plastic. It's bad enough to get bits of epoxy on you.... you do not want it anywhere away from the repair job!

Can you see daylight between the two holes, thru the missing core region?

Christian Williams

E381 - Los Angeles
Blogs Author
Why two holes? Oh, never mind....

Looks like the former craftsman united his holes with a single teak cover in the pattern shown on the deck.

I'd probably glass in the filler disk of plywood, then cover the mess with a similar single teak "decorative piece" over both holes.

Requires oiling or varnishing, but would look nice. And matching deck gel coat perfectly is challenging.

I enjoy working on your boat without getting dirty. :)


Sustaining Member
Blogs Author
If you can get access to the underside a full repair is pretty straigthforward. But very very messy.

As Loren mentioned, the wet core will appear darker from underneath. Cut out the bottom skin and carefully flake out the rotten core. Keep cutting a bit further until you find solid, dry core.

Prepare balsa core material by saturating it with neat epoxy.

Before this kicks off, spread thickened epoxy between the deck and the core material, press core material into thickened epoxy. Fill any major voids with thickened epoxy or bits of balsa and place custom "presser board" as shown below to hold core in place and let cure.

Once cured, fill remaining voids with thickened epoxy and cover over with fiberglass cloth to match thickness of deck, again using "presser board" to hold it all in place.



Frank Langer

1984 Ericson 30+, Nanaimo, BC
Hi Geoff,
A minor point, but it looks as if there is just a screw at the forward end of the handrail in your pic. It doesn't look as if it's covered by a "bung" or any other waterproof material. If that's so, you might want to repair that at the same time so you don't have water leaking down by that screw into your newly repaired section.


Sustaining Member

This is no big deal. Finding all the drips and leaks and fixing them (and the associated long-term damage) is the first project every new boat owner should complete but probably doesn't.

When working with runny epoxy anywhere near/above your factory fabric headliner, DO NOT let epoxy drip onto the top, fuzzy surface of the headliner and cure. Mask completely and protect the top of the headliner (and anything else below) from drips/runs with plastic or cardboard. It's easy to overlook this step when you are focused on the deck core repair above. Epoxy drips/runs will harden into a permanent visible wrinkle in the headliner. Don't ask me how I know this.

I would also CAREFULLY remove those wider teak trim boards on the bulkhead and the last two feet end screws on the thin (long) teak trim to see what is up with the dark discoloring underneath.


Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Trim related note: over the decades when we have cleaned and varnished out our bulkheads, I have not replaced any plugs in the trim battens. It's not very noticeable at all, and most viewers are impressed with the surface varnish and only see this detail when it's pointed out. :)

Also, the only way to clean / refinish the teak surface is to remove the trims anyway. That's also how you access the staples that are securing the vinyl.


Member III
Blogs Author
If you're planning on doing the repair in this colder weather, pick up some System Three Cold Cure epoxy. It cures in a few days down to 35 degrees and doesn't have an amine blush some of the other epoxies have. It's a little thicker than West System, especially in the colder temps. You may get around this by placing the resin next to a heater for a little while prior to mixing it up.

I'm finishing up a recore project on my 25+ before I sell it and have opted to go with the recore from below method. After seeing the oatmeal consistency the core has become, I wouldn't want to handle it any other way. It's a tedious project, but very doable. Let me know if you have any specific questions. or if you feel like driving to Everett, I can show you.


Innocent Bystander
The great thing about CPES is that it is very thin and runny. The problem with CPES is that it is very thin and runny. There is no way to get a meaningful amount deep into that crevasse to seal the edges of the original balsa core without having it run uncontrollably elsewhere in the overhead and liner. I wouldn’t bother. Use regular neat epoxy and just paint it in with a long-handled brush and a prayer, and the confidence that it is viscous enough to not misbehave too badly.

CPES has its uses, but it is not as versatile a material as regular old epoxy. I have a quart of it in my epoxy kit and haven’t touched it in 15 years - although I’ve run through at least five gallons of West System in the meantime.

Tin Kicker

Member III
I'd also not use CPES and go straight to epoxy. CPES is fantastic at what it is intended for, but the remaining core has a high amount of moisture and the CPES will seal it in. That's why a number of us have recommended leaving it open and heated for as long as possible - to dry it out as much as possible.

I'd not suggest going in through the cabin ceiling because getting the fabric back up and looking undisturbed is highly improbable. btdt There are just so many staples buried too deeply to dig out that you run a serious risk of replacing the whole headliner. And if you need to do it to starboard you'll need to match it to port. Here's what the staples look like and your area is just above them.

If this were mine and after digging out everything soft, I'd:

Put large plastic sheets on the floor and settee under the area. (Hopefully already did this before digging the old core out.)

Grind the top surface for the fiberglass patch which you'll want to close the forward hole. Scarf it out to slightly short of what the metal top plate will cover.

Close the bottom sides of the two holes, between the headliner and interior layer of structure, with a piece of aluminum flashing that has a few thick coats of floor wax. The reason I use aluminum is it's cheap, just stiff enough but not too stiff, easily cut with scissors, and won't have a problem with the heat of epoxy. The fiberglass on the cabin side will be rough and the flashing can be effectively sealed in place with a ring of modeling clay around the holes. Not a good place to use tape so press the flashing up to stay in place across the bottoms of the two holes with a long piece of furring strip and a pad of rags on a small flat board. Now you have a one sided repair and stuff won't drain into the cabin.

When working a large area I'll try to generally use what is already there. However, in a limited area like this I would go for one of the options which will not be able to rot if the new chimney installation develops a leak over time. There've been a number of suggestions about what to slide into the new cavity, including shredded glass matt, balsa, plywood, and foam. Another option that works amazingly well is Azek PVC exterior trim (Home Depot or Lowes) with epoxy, but I'd not use it here.

Personally I'd still go with the epoxy and glass matt for a couple of reasons. I've already mentioned the possibility of new rot with the woods. With foam and PVC, you'll be bringing plastic close to a stove pipe. With epoxy you won't have the potential flammability or waxiness that you'll have with polyester resin. If things harden, you can go back at it without a bunch of sanding.

When you have a long thin area that is wide like this the firm core materials generally are hard to get in without leaving large open spaces between them. Have the girlfriend or some other helper mixing small cups of resin and then mixing in shredded matt till it is the consistency of thick mud. While they are mixing, you can be working with paint mixing sticks to pack the mud in and really fill the area.

Because the bottom will be closed off with the aluminum flashing you can fill the two holes.

Lay fiberglass circles on the forward scarfed hole as a top patch.

Let the whole thing cure a day or so, remove the aluminum from below, re-cut the hole for the stove vent.

This sounds longer and harder than it is. Once you think the core has dried and is ready, and have your materials ready, it ought to take just an hour or two.


Advanced Beginner
Blogs Author
Finding all the drips and leaks and fixing them (and the associated long-term damage) is the first project every new boat owner should complete but probably doesn't.
apropos of nothing, I'm sort of amused at the idea that the hunt for drips and leaks might ever be "complete".....

Geoff W.

Makes Up For It With Enthusiasm
This sounds longer and harder than it is. Once you think the core has dried and is ready, and have your materials ready, it ought to take just an hour or two.
Thanks so much for the detailed response/dummy step-by-step. And thanks to everybody, as I sit here and fuss over my "rain patch" and contemplate the life choices that have lead me here.

I've got the holes taped off with heavy duty garbage bags and gorilla tape (though this was not perfect as a nice drip let me know this morning...) and my little space heater set to "fan" mode blowing up into the holes. I'm working on assembling materials and next steps, and hopefully I can get a lucky day or two with minimal rain in the near future to finish this out. Surprise surprise, it's the PNW in January, and it's raining...