Repaired small rotted area of plywood deck

Discussion in 'Wooden Boat Building and Restoration' started by sdowney717, Oct 17, 2021.

  1. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Since I have a lot of wood pieces, did not have to buy any for the repair.
    Of course they built the boat 50 years ago with non treated plywood for the deck, covered with a thin layer of glass. And either the rot started where the rail screws to the deck, or along the cabin side. I knew about for a couple of years, the soft spot. Turned out to not bee too large an area, and the rot was confined to the plywood only. I used PT 3/4 plywood, part of something a neighbor threw away, nice to reclaim it. The panel is in great condition as far as voids saw none.

    I treated the wood with 90% isopropyl alcohol mixed with Boric acid white roach powder and a tooth brush. That kills any fungus and wont let it grow back. It also seems to brighten any dark looking wood. I also liberally poured it into the frame pockets.

    First time posting pics using the gallery embed property
    so this is a test in a way
    All wood is PT, all glue is PL polyurethane
    I had to chip out the rotten toe rail and work around the SS top.
    Moving the SS rail out of the way gave me some room, had to hang left leg over the side of the boat

    First picture is the hole. I also cut the edges at an angle which was not needed. I put in side reinforcements under the plywood edges for added support made from a deck board.

    The patch was screwed in with SS deck screws and glued in place with PL mixed with sawdust. But not too much dust as it will cure too fast.

    Here it is sanded smooth to get ready for the 'glass' and glue.

    The 'glass' is FG drywall tape. I used 2 layers. Since it has a resin back it goes down and stays in place. I put the glue on and then added another layer of glass tape, but was thinking the weave is loose enough could lay 2 layers then glue. But I also thickened glue a little by adding some fine sanding dust into the PL glue

    I used a 4 inch plastic knife to spread the glue into the tape and smooth it out. Since the glue wont stick to cereal bags, I used that to form the edge, so to keep it smooth and not bubble outwards as this glue swells as it cures. Flat areas you can smooth over with the knife in multiple passes over several minutes.

    Cured glue next day

    Sanded smooth using a coarse grit 3x21 belt sander and then a random orbit 40 grit paper

    Primed with Bulls eye 123 Rustoleum white primer paint.

    The repair took about 2/3 of a full cartridge tube of PL glue. I use the 28oz tubes. 1 tube cost 10$. I have a lot of experience using that glue. The glue is not brittle and does not crack and is waterproof, I even seamed all below hull planks using that glue mixed with sawdust back in 2005. No leaks. Boat goes in and out without needing to soak up to seal.
    Last edited: Oct 17, 2021
    philSweet and hoytedow like this.
  2. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Adding that if anyone does this, they really need to mix some fine sawdust into the glue, around 30%. What that does is keep so many bubbles from forming as this is a foaming glue.
    My thinking on how that works is it speeds up the cure so there is less time for those bubbles to form. If they do form, what you do is sand out the bubbles and then go over the top with a light layer of PL mixed with sanding dust. The other advantage of mixing in sanding dust is it extends the glue, you get more out of a tube of glue.
    hoytedow likes this.
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    That is a weak area on the deck. PL and miscellaneous fillers are not equivalent to the original laminate.
  4. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Which was plywood only. That very thin layer of glass added nothing to the strength. The strength of the wood boat is in the wood and the framing. The sheer clamp along the outer rim is a double layer of 1 inch by 4 inch mahogany boards, then there is a frame filler block between the 1.25 by 2.25 inch frames, the 1 inch by 6 inch exteriror planking and the 1.5 inch thick tapered rub rail. There is also a 1 by 2 mahogany strip screwed to the inner sheer clamp that the SS rail screws into.

    The distance of unsupported plywood along its width is about 7 inches. I rebuilt the entire aft end decks of this boat couple years ago , and it is very strong. I got rid of the teak overlay and used the same thin glass and PL glue simply to seal the wood to make it suitable for paint and that the plywood wont check.

    I once had an old fiberglass Chris Craft house boat of about 45 feet hit me in the slip, when our boats impacted, his boat cracked along the edge of its top deck and mine had zero damages. And that was before I rebuilt the aft decking. I honestly think the boat is of a very strong construction, more so than a lot of glass boats on their sides. There is also a nice thick SS rubrail strip screwed onto the rubrail.

    All the glass on the boat is very thin layer simply for protecting the surface of the wood to give it a coating, none of it is structural. In prior years to this, they would have used cotton canvas glued to the decking with paint.

    The boat was built in the transitional years between wood and glass.

  5. sdowney717
    Joined: Nov 2010
    Posts: 1,175
    Likes: 85, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    here is an album of pics when I rebuilt the aft decking and you can see more of the construction. I actually improved on what they did using some thicker pieces.

    One pic shows a paper pattern I made for the plywood which back there is narrow and has a lot of support. I filled in any unevenness with PL mixed was sadust, and laid over that the thin FG tape with PL. Been holding up great.

    The toe rail is next on the list to be replaced. It is badly rotten, but still keeps your toes from going over the edge.

    Also adding, the OEM glass layer on the plywood is the thickness of a cereal box, I can easily tear it with hands and cut it free with a kitchen knife, which is what I did to expose the area to repair. And of course is polyester and not well attached to the wood, but you know 50 years is a long time.
    Last edited: Oct 22, 2021
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