How can I fix this rotten mahogany cabin wall?

Discussion in 'Wooden Boat Building and Restoration' started by LandFish, Aug 17, 2021.

  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I am only talking across Gonzo because we agree in part. Those random shapes are impossible to get right. This is why I said to straightedge them. Then template the curve on top only, or window, if needed, etc. A 3cm bond is great plenty for what you are doing. You do NOT need bevels and scarfs here, unsheathed hulls yes; here, no. The 3cm epoxy bond will never break done as I explained. Where you do need a scarf and bevel joint is on plywood. 1/4" plywood, 2" bevel minimum, 1/2" plywood, use Gonzo's ratio. For wood stacked vertically, 3/4" wood or even 1/2" needs no bevels done well..

    Bevels on strip planking are a nightmare. Avoid them.
     
  2. kapnD
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    kapnD Senior Member

    A doweling jig can help getting the pieces glued into correct position, a biscuit joiner works too, allows a little slop for final alignments.
    I’d be removing the windowframes, as it’s already been mentioned that they’re leaking, and rotting as a consequence.
     
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  3. LandFish
    Joined: Jun 2021
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    Location: Norway

    LandFish Junior Member

    Thanks for all the input guys!

    I am most likely going to disassemble the whole wall starting tomorrow. Just to see what I am dealing with.
    As I said earlier I need to fix this quickly, so I am not sure if I can wait for international shipping of mahogany. There is a place where I can source mahogany locally, but on their website it seems they only have 18 mm or narrower wood. I'll call em up tomorrow and hear if they have anything thicker in stock.

    I am also considering patching the wall up with some other type of wood that is easier to source quickly. And then replace the whole wall with proper mahogany at a later time. I know its not ideal for aesthetics (and maybe some kind of weird wood interaction I dont know about), but I need the wall to be good before winter.

    Also for patching up the plywood for the fiberglass roof sheathing after the wall and roof deck is fixed, can I use plywood that is not marine grade? It seems like it is hard to source marine grade plywood here.
     
  4. fallguy
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    fallguy Senior Member

    Avoid non marine grade plywood. Most birch plywoods are interior grade.

    If you find exterior grade plywood, you can 30 minute hard boil a sample and see if it fails or not.

    The ends of even marine grade plywood should never be left exposed to sun/weather. If you look around the boat, you'll probably either see no edges or see some edges split if exposed. What happens is the thermal expansion rates of the various panels and glues vary too much.
     
  5. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Why do the repair twice?
    Labor is usually more expensive than the materials. Even free labor.

    Tenting will get through the winter.

    This is just the tip of the rotberg!

    What is the sole like?
    Side deck and support system?
    What is holding the roof up?

    Tent it.
    Start from the bottom working up.
    Have a solid foundation for each piece.

    Rot exists one foot along grain and two inches across grain from the visible damage.
     
  6. LandFish
    Joined: Jun 2021
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    Location: Norway

    LandFish Junior Member

    I just want to make sure I retain as much heat as possible in the boat in winter. So something has to close the holes in the wall.
    If I am able to, I would like to only fix once, but as I said I might not be able to source the correct width of mahogany wood in time. Hence why I would do this twice.

    With sole do you mean the floors in the cabin? They are all in great shape.

    With support system, do you mean whats holding the side deck up?
    The supports are good. But where some of the supports meet the under-deck there is some white mould.
    [​IMG]
    The teak deck is in good shape as far as I can tell, but the caulking has cracked in several places so it needs to be redone.
     
  7. Blueknarr
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    Blueknarr Senior Member

    White mold eats wood!
    Everything within two feet of the mold needs to be replaced

    Black mold doesn't eat wood. Just the dust landing on it. Black is toxic and killed with bleach. White may be edible fungi and is also killed by bleach.

    More of the rotberg is exposed.

    What's holding the roof up?
    Is there any rot or mold in the bilge?

    The vessel needs lots of ventilation. Being closed up as a liveaboard, is causing much of the rot.
     
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  8. fallguy
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    fallguy Senior Member

    What is the heating system for winter?

    Different types if heat systems are better or worse for condensation..also where wintering. Propane is horrible.

    get the germicides going
     
  9. LandFish
    Joined: Jun 2021
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    Location: Norway

    LandFish Junior Member

    There are 6 usb fans in different locations in the cabin that are on in the daytime. There is a ventilation hole in the kitchen.

    For heat there is a wooden stove and also a china diesel heater. Though we will probably also use some electrical heating.

    There is no rot or mold in the bilge that I have seen. But the primer (aluminum paint I think) has started to disappear in the bottom of the bilge where there is some water.
    There is some white mould on the frame near the toilet where the big rot hole is.

    I am pretty sure the roof is held up by the walls and the walls are held up by the deck support structure.
     
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  10. fallguy
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    fallguy Senior Member

    Wood and diesel is good.

    Do a good job of closing it in; no foam.

    Get some mold killer. Bleach is not really best anymore.

    usb fans might be a bit too little; consider some bigger ones in the damp areas with mold, although it seems to be from leaks

    I wish we could see a pic of the galley or some nice bit. It is a good looking boat; probably the reason you are getting scolded a bit is it looks like a gem and people hope it can remain that way.

    Best of luck with the work.
     
  11. LandFish
    Joined: Jun 2021
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    LandFish Junior Member

    It is a beautiful boat and I of course want to keep it good looking. You can see more pictures of the boat here

    I am however new to all of this and willing to learn. I don't want to do halfhearted repairs, but I am pressed for time and that can lead to compromises.
    Some things I have to learn the hard way. At the moment I am unsure if I would've bought it if I knew to what extent this boat needed in repairs.
    Especially that the under decks are potentially bad and rotten scares me.
     
  12. gonzo
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    gonzo Senior Member

    You should have someone survey the boat before your repairs do more damage than good. There are many boats that were a good restoration project that end up cut up and burnt because the bad repairs make a restoration too expensive and not worth it.
     
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  13. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member


    No disrespect Landfish. Your nibbling away at the window top is doing as Gonzo described. You are losing information about the shape of the original piece of wood. It is best to remove in a manner that preserves construction details. It will aid greatly in the reconstruction.

    Is the bilge water fresh or salt. (Disgusting taste test)

    Your roof should be supported by the longitudinal walls. Now the starboard wall is missing and no longer supports the transverse roof beams. These beams are now handing from and not supporting the roof decking. Those thin decking strips are not up to the task.

    Your roof is staying up out of habit.

    Normally temporary supports would be installed transferring the roof load to the floor. But the floor is also rotten.

    GET A SURVEY!
    FIND ALL THE ROT!
    FIND THE WATER LEAK!
    MAKE THE BOAT A SAFE PLACE TO WORK!
     
  14. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I own a 1970 wooden 37 Egg Harbor and over 20 years have done some massive wood repairs to the boat.
    I have found treating the wood with 90% rubbing alcohol and adding Boric acid to the alcohol to get a saturated solutions kills the rot and the spores.
    Anywhere I have cut back or replaced rotten wood and used that on the wood, rot has never returned. I fixed several rotting side planks with that mix for example in my 2014 haul out. When you change the environment of the wood that fungus loves, the rot dies.

    I buy the 90% alcohol at Walmart.
    Boric acid is white Roach Powder.
    So after cutting back to what you sense is sound wood, even if it had some rot spores, this boric acid treatment wont allow the fungus to grow back, as it remains in the old glued wood. But yeah, if you do nothing to change the wood environment, the rot just comes back eventually.

    You can even mix Boric acid with hot water into a pump sprayer and spray it all over the inside of you bilge to kill fungus and bacteria and insects.

    I have read other people use propylene or ethylene glycol mixed with boric acid to kill rot, but I think that interferes with gluing the wood.
     
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  15. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Here are some pics of my recent aft side repair.
    The top plank started rotting. Used to have teak covering boards, all that plywood underneath rotted, replaced it all.
    The side of the boat has a rub rail, the 1" top mahogany plank, 1.25" thick frame ends against the plank, 1.25 " spacers between frames, then two 3/4 inch boards to form the inner gunwhale.
    When not rotted, it is a very strong setup.
    I replaced much of the inner unseen wood with treated pine wood, and used treated plywood. But the repair partially failed as the mahogany top started getting wet from rain washing down the boat. So this time I dug all the rotted wood off top of the plank, wire brushed plank edge, then treated with the alcohol and boric acid mix. I lost about 1/4" off the top edge of the plank due to rot.

    Then I used Loctite Black PL roof and flashing polyurethane (black rubber), mixed in around 30% sawdust, and forced it into the whole area of the top plank edge, and capped it off with 1/4 to 1/8" thin strips of treated wood on top of the plank and all glued together with black PL. The sawdust allows quick cures, and also stiffens the rubber. I used some lead weights to hold down the woods strips on top of the plank.

    Then I sanded it all smooth. And used Loctite PL Premium polyurethane and Fiberglass drywall tape to make a covering over the entire area. I overlapped the FG tape maybe halfway over itself across the entire surface and used a wide putty knife to spread the construction adhesive. I also on the edges made the FG tape go up the sides.
    You basically spread on a thin coat of PL, and lay the tape in that, or you can put the tape on first and spread the glue on top of that. What happens is it does swell up the tape and on the wood, so you move the putty knife back and forth over the wood surface while it is setting up thicker and thicker.

    Then I used 40 grit random orbit to sand it all smooth. And then used same putty knife to trowel on a thin smear coat of Dap Dynaflex 230 to fill any imperfections in the glue-fiberglass tape surface.

    I have found over the years this FG tape and PL holds up great with no cracking, and seals the plywood surface, so no surface checking (paint cracking) when painted over.
    Here is the perfectly smooth and sealed PL Premium surface made with FG drywall tape.
    https://photos.app.goo.gl/fJM74xrsbpnDo3un6 20210908_142218.jpg 20210908_142223.jpg 20210908_142211.jpg
    The black PL mixed with sawdust sitting on top of the mahogany plank. The Black PL attaches very well to the rub rail with the eroded plank edge under the black PL, and it is completely sealed, no rain can ever get to the wood plank edge again. The top of the plank had an eroded edge leaving anywhere from 1/8" to 1/4" space between itself and the adjoining treated wood, which never rotted. This Black PL was cured next day due to its hot and humid and I mixed sawdust into it, that forces a quicker cure even in thick layers. It turns into tough black rubber, and can be sanded. I put pieces of cereal bag under the lead so it wont get stuck in the Black PL.

    20210907_123032.jpg
    Final view before final paint with DAP smeared over the top of the glue.
    I will lightly sand that and then paint in a few days
    Dap-top-plywood.PNG
     
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