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I am having a bit of a sap/gum problem with my Oregon tabletop which at the moment I have left raw (unfinished).

Picture of my tabletop

The timber is very well aged (at least 20 years), quartersawn thick originally, now it's been put through a thicknesser it's about 60mm thick. It came from some massive beams which were salvaged from a collapsed building after an earthquake in another part of the country. I've previously used quartersawn wood from the same batch as massive shelves which I finished with Danish Oil and which came out brilliantly.

I would have oiled this tabletop too, but it needs a lot more sanding (by hand!) to get it perfectly even and level and smooth enough to oil (the laminate join between the two bits of timber that make up the tabletop is lower than the rest of the tabletop, it should have gone through the thicknesser a few more times AFTER being joined, but that's wasn't feasible), and unfortunately the weather isn't reliable enough to do that for another couple of months. Plus, it just cool just being raw timber as it is right now.

The sap has only come out in the last few days, and I am sure it is because I have been turning the heating up to stay warm. It's doesn't come off at the touch and it smells fine, so it's not a massive inconvenience, but I was wondering if anyone could give me some advice on how to 'cure' the sap? I would prefer to stick with my plan of oiling the tabletop, but I could varnish it instead if that is a more reliable option. But, like I said, I have used this timber elsewhere and finished it with oil and I have had no problems.

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  • While pine was the focus of this question I think the answers still apply here. Seal it with heat to be certain!
    – Matt
    Aug 19 '15 at 3:02
  • @Matt So you think a heatgun would work okay?
    – Benjamin R
    Aug 19 '15 at 6:48
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    You will find that a hand plane can level your tabletop with a lot less effort (and sawdust) than a sander will. I understand that not everyone knows how to use one or has one tuned up and ready to use, but it's worth considering.
    – grfrazee
    Aug 19 '15 at 13:01
  • I think a good heat gun could work. It need to get hot enough to set the sap.
    – Matt
    Aug 19 '15 at 13:12
  • @grfrazee I have already built some very large sanding blocks, approximately 700x275mm with the sandpaper glued to 18mm MDF with a 45x75mm bit of framing pine screwed on back which gives you a good hand grip, which I use diagonally across the grain of the table top inspired by the hand planer approach. With 40 grit paper it works very well. Honestly when the weather changes here (Auckland, NZ) I will take it outside and sand the rest of it up that way, it's good exercise and it's guaranteed to come out even. (If I used a hand planer I would screw it up for sure, if I had one!)
    – Benjamin R
    Aug 19 '15 at 23:26
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Oil as planned, then seal with shellac? If shellac will stop knots bleeding through paintwork applied over it it could similarly prevent gross penetration of sap like this but only time would tell if this worked. To be an effective barrier the shellac couldn't be just a thinly wiped coat so it would of course change the look of the piece fairly significantly.

This sort of thing happens less frequently these days because of kiln drying being so common to quickly get wood down to workable moisture levels, and the heating 'sets' the sap in the wood (basically converting it to a harder, crystalline form, which is a permanent change).

You can mimic the effect to a degree with air-dried wood by just allowing it to get to a high temperature, even by sitting it in direct sunlight (the temps required are quite low, below the boiling point of water in fact).

It's possible that you may be able to locally treat the wood by heating with a heat gun, without much risk of scorching the wood. In theory you might also be able to do this with a domestic iron but I don't know how deeply the heating would need to go to solve the problem.

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  • If sunlight is enough heat I guess an ordinary light bulb in close vicinity would do the same. Or heat a cooking pan with water in it to 80 degrees (we're talking Celsius here) an put it on the knot. I doubt 80 degrees would change the wood (ok, ok, 60 degrees then) but warmer than sunlight. Just my 2pc.
    – LosManos
    Aug 19 '15 at 14:12
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    @LosManos, "I doubt 80 degrees would change the wood (ok, ok, 60 degrees then) but warmer than sunlight." as anyone who has had their legs scorched by a vinyl seat cover or a car fender on a sunny day knows, sunlight can get some surfaces hot enough that they're too hot to touch; that's well above 60°C. If the wood were too pale and reflected too much light to get to a sufficient temp it could be draped in dark-coloured fabric to maximise the effect.
    – Graphus
    Aug 19 '15 at 16:04
  • @Graphus That's a very sensible use of free thermal radiation there.
    – Benjamin R
    Aug 19 '15 at 23:20
  • I can't do the shellac method and oil for the reason you say: it will stand out too much. I will try using my heat gun on it, especially since it is mostly hardened already, but in the final conclusion I would settle for varnishing it. It's kind of a waste of this kind of wood though, being all thick you want as much off the character of the timber to come through, hence why oiling is my preferred option.
    – Benjamin R
    Aug 19 '15 at 23:38
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    @BenjaminR, re. the shellac, I don't think I was clear I meant shellacking the whole top, not just the problem areas. So in essence not much different to varnishing the piece, only with less water-resistance at the end. If you do end up going with varnish and want it to look a little less obviously varnished rubbing down the finish with fine steel wool can be very effective.
    – Graphus
    Aug 20 '15 at 8:58

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