Plugging old holes in wood - best practice?

Discussion in 'Sailboats' started by OrcaSea, Oct 31, 2014.

  1. OrcaSea
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    OrcaSea Senior Member

    Hey all,

    In my restoration I have some #10 & #12 screw holes in wooden structure that I do not want to re-use due to bad edge margins, etc. My instinct is to glue in dowels. What is the best way to fill & seal them and try and maintain some strength, if not with doweling?

    Also (in the same area) the hole for the bow eye was drilled a little crooked and off-center, which always bugged me. It is a 7/16" hole in a 3" X 3" oak knee. Now that the area is exposed for other repairs can/should I plug this and re-drill a straight hole elsewhere? Or try to maintain the strength of the knee, re-use the hole and accept that it's just not going to be straight? (I hate to do this as it will be a reflection on my workmanship).

    It's just a 16' sailboat for fair weather pleasure sailing.

    Thoughts?

    Thanks!

    Curtis
     
  2. gonzo
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    gonzo Senior Member

    Dowels would work. However, if it is a varnished area and you want a better finish, bungs are the way to go. The difference is that dowels have the wood fibers along the length and bung are sideways so they can blend in.
     
  3. PAR
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    PAR Yacht Designer/Builder

    To restore a fastener hole you drill it out, until you know you're back into good wood, which sometimes can require a pretty big hole. Wet out the hole with epoxy, let this sit for several minutes, then wet it out again, insuring the hole has sucked up what it can, into the freshly exposed new wood. Using a species similar to what you're repairing, wet out a dowel, the same diameter of the hole you just drilled. Not a tight fit, not snug, but simply the same size dowel as the hole. Mix a little milled fibers and wood flour into you epoxy and apply inside the hole, just as you stuff the slippery, but clean fitting dowel (the dowel should slide in easily all goo'd up). Hammer lightly until it "sounds" home. Leave this alone until it's cured, then chisel the dowel off flush with the surface, as it's now ready to receive a new fastener.
     
  4. SukiSolo
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    SukiSolo Senior Member

    Common problem. Generally it is good practice to fill with 'core plugs' - cross grain cut pieces. Depth does not matter, you just glue one on top of another until the hole is filled over depth. When the glue is cured, you slice off the top with a chisel and sand flush. This mode is good for repairing 'worn' screw holes too and you can get crafty and use a harder timber for the plugs so you get better screw retention. I use this mode sometimes for dinghy stem fittings where the holes are a bit loose.

    Cosmetically if you can find a similar (ideally same) timber you should get a good colour match BUT note the grain orientation as you must align the grain of the plugs with the original timber. I also tend to use as an adhesive, Aerolite 306 (urea formaldehyde) for these, as it is glass clear, rather than epoxy which tends to leave a dark ring. The urea is a little more forgiving about moisture content in the base timber too compared with epoxy, so if you are not 100% sure of the moisture content, it may be a better bet.

    Dowels are better when engineered to take side load. Note you must drill out the full depth of theoriginal hole and fil to achieve this. Also be more aware of the extra requirement to seal the end grain properly.

    Structurally, if you use cross grain plugs the timber should loose no strength compared to original configuration, unless you have a lot of them. One tip is if you want very clean holes, plug first with a sacrificial filler and use a bradpoint drill. You can get quite a few different sizes of plug cutter, but will need a pillar drill to use it. I have about 4 sizes from 9/32" to 12mm and use all of them depending on job.

    To do a 2" deep hole with 10mm (3/8" approx) plugs may require say 5 or 6 stacked plugs but will be as sound as if the wood was new. Common areas for renewing the timber this way is keel bands and shroud fittings. Was working on one, like this yesterday as it happens.
     
  5. OrcaSea
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    OrcaSea Senior Member

    Thanks guys. Great info!
     
  6. PAR
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    PAR Yacht Designer/Builder

    When repairing a hole, the idea is to repair just the hole, not to bond things, which is what a trunnel does. Don't confuse a dowel with a trunnel. A trunnel is a wooden nail, often wedged at the end, a dowel simply replaces what's been eaten up by rot or fastener movement.

    Cosmetic considerations can be handled several ways, but under bright finishes a bung is the usual course, if the material is thick enough to accept a screw head and bung, with enough meat left, so it (the fastener) still works mechanically. Typically this is 3/8" (9 mm) with hardwoods and 1/2" (13 mm) on softwoods or deeper (depending on how soft).

    I've seen the stacked plug method and it works, but I always worry about voids and compression between the plugs, so I usually "bond" a repair, full length into the hole. It it's the same or a similar species, you'll restore the hole's original pullout attributes, but as noted by Suki, moving up to a denser species can offer a better pullout quality to the fasteners, say for example, using Douglas fir or SYP dowels to replace worn out fastener holes in a Sitka spruce mast, which is known for lousy fastener holding power.

    In the end it's a multi step process: clean the hole of rot, punked or crushed wood by drilling oversize, bond in a suitable replacement using the adhesive as bonding agent, not a tight dowel in the hole fit, as a mechanical lock, then treat the cosmetics issues as required, once the hole is able to support a fastener again.

    If replacing planking (or anything that's attached to anything else) and needing to restore the holes, both the individual elements are treated separately, meaning the planking fastener holes and the framing holes (as an example), each have restored holes, making them a continuous wooden piece again, ready for new fastener holes to be drilled, as required.
     
  7. OrcaSea
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    OrcaSea Senior Member

    PAR, if you haven't written a book, you should; I would buy it.

    Luckily, there are no cosmetic considerations in this particular application, but the advice is going to come in handy when I get to finish brightwork.

    I very much appreciate the responses.
     
  8. philSweet
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    philSweet Senior Member

  9. OrcaSea
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    OrcaSea Senior Member

    Thanks, Phil.

    I don't have a drill press as of yet, but as this project moves on I am going to have to start cruising Craigslist for one as I will need brightwork bungs eventually.

    I was looking at vertical grain lumber for floor slats today and I think I could get both a serviceable used band saw AND a big enough timber to resaw my own for the prices people wanted for vertical grain 1X4's...

    Besides, any excuse to buy tools, right ;)
     
  10. sdowney717
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    sdowney717 Senior Member

    I glue in bamboo, chop sticks and skewers for stripped screw holes. I typically use PL Premium simply because it is convenient, works, and is a swelling expanding glue.

    I have packed them to repair fairly large holes in frames and the wood holds screws fine. I had my doubts till some on WBF suggested them. The fibers they are made from, somehow the screws hole very well.

    No problem also using them to fill a wooden hole in a plank, done that also.
     
  11. sdowney717
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    sdowney717 Senior Member

    I have bought plenty of those cheap plug cutters, and if your cutting hard woods, they do not last long. Better than nothing I suppose.
    I have had them overheat and warp on me.

    I found a very heavy duty plug cutter at a woodworking website and that lasted much longer.
     
  12. philSweet
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    philSweet Senior Member

    I got my vertical grain floor slats out of 4 x 4 white oak. Had the stuff resawn and sanded where I bought them at the local hardwood vendor down the street. 3/8" will span between floor timbers on 12" centers no problem. It wasn't perfectly quarter sawn by any means, but good enough for me.
     

  13. SukiSolo
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    SukiSolo Senior Member


    Cheap, usually Far Eastern origin cutters are false economy, as cutting a few plugs in oak will tell you.....;) Good ones are not so much more and last well. Don't even get me started on needle files (buy Swiss) or F Clamps (DIN 5117 only) or other rubish so called 'tools'.

    PAR, I don't worry about the bond on stacking but then I do pare the plugs square with a chisel (if necessary) so I know there are good contact surfaces and no voids. Tapping home with a drift closes any void(s) up very well. Totally with you on putting say mahogany into WR Cedar or Obeche, Spruce etc to get better screw grip, especially where the 'cosmetic' is hidden ie painted.
     
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