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Approximately 3 years ago I purchased a slice of a log, approximately 50 cm (~1.5') wide at the widest place, approximately 2.5-3 meters (~9-10') long, and about 4-5cm thick (I don't have exact measurements with me right now, will add them in a comment later, if necessary and will add photos if necessary, also later). I think the wood is pine, but am unsure at this moment. The piece was cut into two pieces (~2m and ~1m).

One was treated (by me) with an oil based coating ("Yacht Varnish") with two or three (can't remember now) fairly thick coats, from all sides. I don't know whether this is a mistake or not (let me know!) but I did not fill the imperfections first, but rather tried to put enough of the varnish to coat them as well.

The other, after some time, was treated with two coats of water based laquer which gave is a nicer matte finish, in order for it not to be exposed to the elements.

The long piece was attached at the ends (screwed with 2 corner joints on each end, such that it was resting on the joints) to a wall and a concrete column. The shorter piece did not find a use.

After about a year the shorter piece developed a crack along the middle, with the grain. I did nothing about it. After we moved I turned the bar piece into a bench by screwing 4 feet into it. I did not remove the corners from the wood as I thought it might ruin the thread there, and allow moisture to enter the wood (planned to use them to add hand rests at the ends).

Despite the fact that it felt very sturdy and that people sat on it a handful of time for a total time of maybe an hour, the board developed a fairly wide (3mm I think, at its widest) crack along the grain, around the middle of the bench.

So, I have two questions: 1. I presume I treated the wood badly or this would not have happened. What should I have done differently? 2. What can I do now to stop the crack from spreading and to make the bench safe for sitting without fear of breakage? Most of all I want to avoid sanding it again as I don't have the proper place to do it and don't want to breath wood/lacquer dust.

In regard to Q. 2, I thought about adding a frame undernear, shaped as H or as a rectangle. I thought that maybe the crack didn't develop earlier since the corners did not allow the wood to expand, and now that there is nothing holding them, it did expand in an uneven manner? or perhaps that the presence of the corners did not allow the ends to expand with the middle, and it was bound to happen anyway, with the way it was affixed?

Thanks in advance for all the answers!

Edit:

Just measured: The cut piece is ~1.5m x 40cm x 4cm. The largest crack is about 1 mm wide and 50cm long.

Photos: The crack at the end I think has been from some time after cutting the smaller part off and before the varnish: Bench (http://i.imgur.com/CgnBjeM.jpg)

First part of the crack (it is one long crack with varying width): Crack (http://i.imgur.com/AeAREE3.jpg)

Second part of the crack: Crack 2

  • Please add photos. – Tester101 Oct 19 '14 at 12:07
  • I added the photos. Let me know if you need more info. – Shwouchk Oct 19 '14 at 21:45
  • What do you mean by "repair"? Do you want it to be invisible? Or is keeping it from getting larger/longer good enough? – wallyk Oct 19 '14 at 22:27
  • Thanks for all the answers! I do mainly want to make sure the bench will live long (and be safe to use) rather than hide it. As there are a bunch of other cracks along the wood anyway, I don't mind the look of another one. – Shwouchk Oct 20 '14 at 8:53
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The attached pieces and legs may have exacerbated the effects by not moving with the seat but a piece of pine of that size was probably destined to crack regardless. You can try to weep glue down into it (run a line of yellow glue over the crack then blow it down into the void with an air nozzle) and then clamp out the space but it probably won't be permanent and you could damage your finish with the clamp pressure. Were it me, I'd fill the crack with tinted epoxy and let the piece wear the crack like a badge of honor. Think of a piece reclaimed pine: enter image description here

  1. Tape off the crack with painters tape. You don't want epoxy all over the finish, just down in the crack.
  2. Mix a 5 minute epoxy to the manufactures specs, then add 5% by volume a Van Dyke Brown (or similar) aniline pigment. Most manufacturers will recommend a product compatible with their own on their website, I recommend West System.
  3. Apply the mix carefully over the crack and then force it down in with a putty knife or shim. Trowel off the excess as neatly as possible and let dry. Repeat this step as necessary (sometimes is sinks in after application) until the epoxy fills the void flush with the surface.
  4. Remove the tape preferably when the epoxy is still sort of gooey and let dry over night. (yes it's 5 minute epoxy but trust me)
  5. Sand off the residual epoxy with 220 and a light touch and then scuff sand the entire piece with 280.
  6. Apply a light fresh coat of your original finish.

Hope this helps, cheers!

  • Agreed, it was "destined to crack". – Mazura Oct 19 '14 at 23:53
  • I know right? I've never seen a piece of pine wider than my thumb that didn't try to check itself into oblivion. It must start out with a higher moisture content than most species. – user23534 Oct 20 '14 at 0:02
  • 0. Use paper in hand, hand tool, or power tools when sanding? 1. If possible, I'd like to avoid sanding as I'm afraid of the dust (and it's not fun). Would it be possible to make this approach look fair without sanding (e.g. by careful placement of the tape and careful application of the epoxy, or a more liquid type of epoxy)? 2. What wood type would be less likely to crack with time? Would Oak? 3. Do you think this approach would also be appropriate for the short piece, which is almost cracked in half? There it might also be easier to use the glue approach as I'm less afraid about the finish. – Shwouchk Oct 20 '14 at 9:13
  • You can use a random orbit sander for the 220 but hand sand only with the 280. I've never had any luck smoothing epoxy out enough to go without sanding, even if you could it doesn't quite look like finish anyway. As far as dust goes, wear a respirator and have a friend hold a vacuum while you're working and it shouldn't be too much of an issue. Yes hard woods seem to be much less susceptible to checking. – user23534 Oct 20 '14 at 18:38
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Another traditional approach to reinforcing cracked wood is to install a "butterfly key" (also known as "bowtie key"). This is essentially an inlaid piece that acts as a pair of dovetail joints to tie the two sides together. Keys can be as larger or small as desired, in similar wood or contrasting wood ... the latter is a bit more common since the key's grain direction is different anyway.

Inlaid butterfly key in dark wood against a lighter wood background

Websearch will find info about this technique; the site I swiped this image from is https://www.canadianwoodworking.com/tipstechniques/butterfly-key

  • Thanks! From the looks of it, this technique is not appropriate for a bench, as it would not be comfortable for sit on it? Also, and it might just be the image, but is this appropriate for longer cracks? – Shwouchk Oct 20 '14 at 9:17
  • After reading the guide you linked, I understand that the piece of red wood is level with the boards, and is set inside them. – Shwouchk Oct 20 '14 at 9:27
  • That's correct. It isn't a bandage, but a suture. <smile/> – keshlam Oct 20 '14 at 12:30
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1/4" steel flat stock, one under each end, cut to width. With counter sunk holes for short, pan-head lag screws. Fancy installations will have an area routed for this piece, making it flush to the surface. Ideally it runs under the legs, sharing two out of the four fasteners per leg. Sort of like this:

enter image description here

enter image description here

  • 2
    I can't tell from your description which way you propose attaching the steel stock, but I would not recommend affixing something perpendicular to the grain. Wood will shrink and swell with temperature and humidity, and fastening it to steel like that will just exacerbate the cracking. – Hank Oct 20 '14 at 1:32
  • @HenryJackson, good points. My solution is more for when it does crack in half, or if you're really worried it could, haphazardly. – Mazura Oct 20 '14 at 2:45

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