Nov 27 2020

Splitting Planks 3: Selecting Wood

Published by at 8:44 pm under Wood Working

This article will mainly concern Scotch pine (Pinus sylvestris) and Norway spruce (Picea abies). Related tree species are likely to behave similarly and there might be others where at least parts of the information will be usable.

There are several qualities/considerations in selecting wood for planks. A lot of the information is also relevant for log cabin building, where the requirements are less strict.

Density

The density of the wood is very important when splitting planks. Too loose grown wood will be problematic to split. They will tend to run off to one side fairly easily. Extremely dense wood, especially spruce, will also have this tendency. The best wood generally has growth rings of about 2-3 mm. Denser wood is more durable than soft wood and this is an additional consideration. Especially for wood that will be directly exposed to the elements.

Another function of density is interlocking grain and compression wood. If a tree grows on unstable ground it will tend to tip a tiny bit back and forth to correct itself. In doing so the leaning action will create pockets of compression wood, which makes the wood exceedingly hard. These trees are not nice to split, but will make very good logs for log cabins. The stump portion will generally have interlocking grain, especially on pine. Because of this you want to split the pine from the top portion to get more leverage at the root.

Compression wood is very dense and brittle wood that develops underneath conifers which lean over. Although you can hew shorter logs straight, it is best to avoid compression wood as far as possible, because it will never lay still, but keep contracting and expanding due to air moisture. Because of the brittleness it can also easily make a split run off where it encounters it.

Resin Content

Not a consideration with spruce at all, a high resin content will make boards and logs more durable in pine. Heartwood is always fairly resinous, sapwood usually much less so. For the most exposed parts of any building, use the highest resin content wood as possible. Almost glossy in appearance. Good sources are tops of lightning killed trees or highly damaged, old trunks. Most exposed places in a building will be edges of roofs and the logs closest to the ground. Highly resinous wood is usually more brittle and can be more difficult to split thin without breaking. Expect to hew such logs a fair bit to final thickness.

Age

With pine the general rule is that the older the better. At least in terms of durability. However, with age over 200 years they will tend to start twisting more and the entire trunk can become less straight. Although this old pine was exclusively used in the medieval period due to a very high availability, I never cut those trees. They are too biologically important these days when there are so few of them. Spruce I do not care if I cut at any age since it almost never lives longer than 120 years and is taking over more and more habitat from the pine. Very old spruce, and occasionally also old pine, will tend to become hollow inside. When it has become hollow the tree is useless both for log cabins and planks. Although the rot is often only at the base, I will tend to leave the trees for the woodpeckers if I discover rot or a hollow cavity inside while felling.

Picture below is of a mature tree, with a flattening top.

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Straight Grain

When splitting wood for planks straight grain is an enormous advantage, but not an absolutely necessary. It depends a bit on which method is used. I plan to show both methods in later posts. With the end splitting method, the grain must be very straight, unless the boards you need are exceedingly short.

So how to see if the trees are straight splitting before felling them? I have seen and heard of all kinds of methods for it, but none are perfectly reliable. If it looks spiraled even on the bark, then you know that it will not work well so you might just leave it. Those are however extreme cases and you can get pretty spiraled trees without really being able to see it on the bark. The first 1-2 meters might twist more as well and the rest of the trunk can be relatively straight grained. In the old days they often discarded those first metres if it showed itself to have too spirally grain.

The best methods I have found are either to split a branch and see how much it twists or after felling, to split a metre or so length in the top section and see how it behaves. When you are building a log cabin, straight grain is not a consideration and when you are building you can hand pick the straightest ones for splitting into boards.

The way it turns is however a consideration for log cabins. In the northern hemisphere you never want to use timber that spirals clockwise (looking from the base)  in your timber cabin. It will crack much more deeply when drying and will never lay still, but twist back and forth according to the air moisture. This can cause the joints of your log cabin to get out of alignment. How it works in the southern hemisphere I don’t know. But I would imagine it could be the opposite.

Below is an example of a split branch of the spruce directly behind it. As you can see this tree is unlikely to split perfectly straight, but probably will not be incredibly twisted either.

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When to Fell

In the very old days they often felled the timber in the early spring and let the needles die on the tree before limbing and removing the bark. In later eras they were more haphazard about it and generally felled during the winter because of easier transportation on the snow. The formerly mentioned method is however advantageous in that the wood in the future will develop very small cracks rather than large ones and that it will not warp. As a sidenote it is worth mentioning that this is also absolutely essential when using certain deciduous woods like elm or aspen. Both of those will warp unrecognisably when drying if  you work them completely fresh. This is very important to remember when making bows out of elm. Even if the leaves are dead, the bark will usually peel well if not left too long.

Regards
Torjus

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