Cracks

Previously we wrote about types of wood (wet, dried, laminated) and the shrinking of log houses and how we deal with the shrinking. In this post we want to show a little more about the actual drying process, and cracks. Because drying and cracks are very much related.

Why Does Wood Crack?

The photo below shows a crack in a wooden disc. Why does wood crack like this? Very simple: drying.

cracked wooden disc

cracked wooden disc

When wood dries, the drying process starts at the outside of the logs. While the humidity goes down from 15% to 12% near the outside of the log, more to the the center of the log the humidity initially remains at 15%. And that is a problem.

To explain we need a little math. To do the math completely correct we would need integral calculus, differentials and all that stuff. We think that is a little over the top and also, to be honest, your author has competely forgotten this part of calculus since high school.

Fortunately a spreadsheet can help and instead of differentials we will create a small table, that will do just as fine. In the table we show the humidity percentage in a 32 centimeters log, going from 15% in the center of the log to 12% at the outside of the log (column A). Let’s assume the wood shrinks with a maximum of 3%, so near the center there is no shrinkage (shrinkage factor 100%) but at the outside of the log we have a shrinkage of 3% (shrinkage factor 97%, column B).

A B C
row humidity percentage shrinkage factor diameter after shrinkage
1 15.00% 100.00 2.000
2 14.80% 99.80 1.996
3 14.60% 99.60 1.992
4 14.40% 99.40 1.988
5 14.20% 99.20 1.984
6 14.00% 99.00 1.980
7 13.80% 98.80 1.976
8 13.60% 98.60 1.972
9 13.40% 98.40 1.968
10 13.20% 98.20 1.964
11 13.00% 98.00 1.960
12 12.80% 97.80 1.956
13 12.60% 97.60 1.952
14 12.40% 97.40 1.948
15 12.20% 97.20 1.944
16 12.00% 97.00 1.940
 TOTAL 31.520

The table goes in 2 centimeters steps, and if you take a look at row 10 you will see that the original 2 centimeters thickness of that layer has shrunk to 1.964 centimeter because of the 98.20% shrinkage factor.

At the bottom of columns C we add up the “shrunken” diameters and we come to a total diameter of 31.520 centimeters, so that is the new diameter of our log. The circumference can now be calculated: the actual circumference of our log is 99,023 centimeters.

But wait a minute: the wood at the outside layer (row 16) has shrunk 3%, so the original circumference was 100.53 centimeters (for 32 centimeters diameter) and now there is only 97% of that 100.53 centimeters left, which is 97.515 centimeters.

Here we have the problem: the actual circumference of the shrunken log is 99.023 centimeters, but there is only 97.515 centimeters of wood available in the outside layer to actually go around. And that is where it cracks.

Can You Prevent Cracking?

Yes, and it is not that complicated. For non-laminated wood the solution is to take more time when drying the wood. Much more time. Actually so much time that it becomes almost impossible to dry non-laminated wood. So non-laminated wood almost always has cracks.

The other solution is to laminate the wood. Cut it to 4 centimeter planks, dry it, then put it together again. No cracks, no warping, no bending, problem solved. That is what Lithouse does.

Is A Crack A Problem?

Some people say yes, others say no. The author of this article likes cracks as they enhance the visual appearance of the wood. Wood is a natural product, and a crack is ok.

But most people dislike cracks. Cracks collect dust. Cracks decrease the thermal insulation of the walls. Cracks on the outside can be a problem because, not only do they collect dust, but also they collect grime and water, and that is where things can start to go really wrong. Cracks on the outside must be closed, or caulked.

So while the author likes a crack here and there, the consensus at Lithouse is that we should avoid them. Actually laminated wood always has much fewer cracks than non-laminated wood because of the more even drying process. Caulking cracks on the outside of a Lithouse log house will never be necessary, because our houses have no cracks on the outside. Simple.

Last Example

Below another example of a NON-laminated log. For sure it has cracked. No worries, Lithouse uses laminated logs and you will not see cracks like this.

Another cracked non-laminated log

Another cracked non-laminated log