finishing bright mahogany classic runabout

Discussion in 'Materials' started by H A van Nes, Feb 15, 2015.

  1. gonzo
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    gonzo Senior Member

    Epoxy in the seams will create structural problems. Either you encapsulated the whole hull and deck, or you need to allow for some movement. Otherwise, when the wood gets moist and swells, the epoxy will crush the fibers. Next time it dries, the gap will be bigger.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Typically when you run into this problem you only have a few choices. The first and most obvious is to reef out the seams or reshape them. If you reshape them, you can grind up a circular saw blade, to remove the cant in the teeth and cut a new seam of the appropriate width and depth. Naturally, reefing out the seams and recaulking is self explanatory.

    You can also "spine" the seams, which works well on moored carvels. This is more work, but makes the hull tighter. This entails making the seams uniform in shape, typically slightly tapered. A wedge of the same type of stock that the planking is, gets glue and is hammered into place (tapered seam thing), usually standing proud a bit. When the glued is cured, the wedge (spine) is planed flat and the hull faired. Spined seams generally look better under varnish.

    Are you sure this is a carvel build?
     
  3. SukiSolo
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    SukiSolo Senior Member

    The Oxalic won't do anything much to the timber adjacent to the 'stain' areas. Worth using repeated coatings as this does help. It's not a silver bullet for removing stains but can work very well on some. I've also found that some timbers respond better, but it also depends partly on the cause of the stain.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Oxalic acid is a tough recommendation for most novice restorers, as mixed results are the best you can get. I've had some successes, but also have screwed the pooch on a few jobs with it too. The usual result is a lighter colored stain, with mad attempts to blend the area into surrounding areas, less offensively than was previously possible. Generally, when faced with these types of decisions, it's best to look at the effort and results possibilities first, as it's typically a lot easier and cheaper to replace the offending piece(s), then to restore them. What I tell folks is, unless you have documentation that JFK was doing Marilin Monroe aboard this boat, so need to preserve it's intrinsic value, you'd probable be better off simply replacing the piece.
     
  5. H A van Nes
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    H A van Nes designer builder sailor

    Thanks guys: Concerning this comment and the last one by Gonzo, maybe I mislead you by accident. The boat is essentially cold molded on the topsides where the problem is - 1/4 inch marine ply over the frames and approx. 7/16ths solid mahogany planks epoxied over that and to each other with wood flour thickened epoxy. These 7/16ths planks for the outer topsides and are placed together like carvel planking without caulking. Just a few of the seams are cracked on the outside. There have never been any leaks through the topsides in ten years since launch. The vast majority of the seams have not cracked. Many of these good seems are as much as 1/8th wide. the largest cracked seams are 1/8th wide. There is no evidence of any cracking or separation between the outer planks and the marine plywood underneath. Do you still think it unwise to clean the cracked seems, wet down with clear epoxy and fill with thickened epoxy?
     
  6. H A van Nes
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    H A van Nes designer builder sailor

    how about the cracks between the planks

    Thanks again Par. As I mentioned the outer planks are epoxied to the inner 1/4 in marine plywood and also epoxied to each. A few of these outside joints have opened up ( the worst is about 1/8th open). How should I fill those cracks before varnishing? Thanks in advance for any help you can give. BTW I have, and am reading Rebecca Witman's book.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Filling cracks on a molded boat and expecting to have a fine, bright finish is a crap shoot. The basic problem usually is the filler material, just looks terrible under varnish. The only way that I've found that can work is to create a slurry of the same stuff. Simply put, if the planking is mahogany, you'll make a slurry of mahogany dust. You can use the wet sand residue, which is a common way to seal the course grain of mahogany. You scrape the slurry into the grain, let the solvent flash off, then apply varnish. The varnish will lock down the grain filling dust. Some like to make a filler, using diluted varnish, maybe a splash of Japan drier and of course the appropriate dust from the stock you're finishing.

    Goo's in a tube will work, but finding one that is sandable AND stainable is the butt kicker. They just don't take color from stain or varnish like the surrounding wood, so they stick out like a sore thumb.

    Lastly, and something that takes some serious experience is tinting epoxy. You can effect a repair of the cracks, then apply a tinted epoxy over coat on just the cracks, so the color is the same, but this takes a lot of practice to get right.
     

  8. H A van Nes
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    H A van Nes designer builder sailor

    Thanks again: I was planning to do this with wood flour from the boat. Witmtan suggests exactly the same thing. In fact there are other wide 1/8th seems that were always that big and filled with the same wood flour and epoxy mix that was used originally to secure the planks. Most of these have not opened up. they can easily be seen after varnishing but they look OK. I'm trying to figure out how to post a picture here.
     

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