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 we can arrive at the same result with a simple spreadsheet. In the table below we take a 32 cm log as an example. Diameter is 32 cm, so the radius is 16 cm. The first line of the spreadsheet is the centre of the log. Humidity percentage is 24%, and this first centimeter still has a thickness of one centimeter.

But the next centimeter is a little drier: 23,6%, and also a little shrunken. The original one centimeter has shrunk to 0,999 centimeter. Every next line is a little drier, and a little thinner. When we arrive at the outside of the log (line 16) all that remains of the original one centimeter is 0,985 centimeter.

 

afstand tot kern vocht-percentage oorspronkelijke 1,0 cm nu gekrompen tot
1 cm 24,0 1,000 cm
2 cm 23,6 0,999 cm
3 cm 23,2 0,998 cm
4 cm 22,8 0,997 cm
5 cm 22,4 0,996 cm
6 cm 22,0 0,995 cm
7 cm 21,6 0,994 cm
8 cm 21,2 0,993 cm
9 cm 20,8 0,992 cm
10 cm 20,4 0,991 cm
11 cm 20,0 0,990 cm
12 cm 19,6 0,989 cm
13 cm 19,2 0,988 cm
14 cm 18,8 0,987 cm
15 cm 18,4 0,986 cm
16 cm 18,0 0,985 cm
totale straal na droging: 15,880 cm
nieuwe omtrek: 99,7770 cm

So far so good. We add up the thicknesses after drying and now we arrive at a total radius of 15,880 centimeter. The circumference of our log is 2*pi*15,880=99,777 centimeter.

But wait a minute, de wood in line 16 on the outside of the log has shrunk so much that there is only 99,0230 centimeters left to go around the log. And that is where we have the real problem. The actual circumference is 99,777 centimeter, but the outside layer can only accommodate for 99,0230 centimeters. That’s a crack!

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