Timber in winter

[haavard]

By decking I mean pressure-treated wood used for patio floors.

Why be so conventional?
I have just used a bunch of larch decking. It hasn't been treated with anything other than what the larch itself has produced.
And soon I will start a thread about oak decking - it is also as clean as a baby's bottom.

 

[KnockOnWood]

A little tune is never wrong

https://www.youtube.com/watch?v=8l_4u7vQBGI

 

[falkn]

I would say that heat or cold changes the moisture in the wood, so it's not really the temperature after all

This is not a matter of opinion; it's physics. Shrinkage and swelling due to moisture and temperature are two different things. The fact that swelling due to relative humidity is dependent on temperature is one thing, but the dependency does not apply in reverse. A steel rod, for example, doesn't bind moisture but still becomes longer with increased temperature. You've probably heard about rail buckling on train tracks; that's because of this. I have personally had lab sessions during my studies where we measured this for different types of timber.

 

[AskeHolst]

But different materials change size differently depending on temperature. A steel rod in a solid phase becomes larger with increasing temperature, water becomes about 10% larger when the temperature goes below zero and it changes phase to ice. So it's probably not a simple relationship in a complex material like wood. I wouldn't be surprised if frozen wood shrinks when it thaws.

 

[falkn]

But different materials change size differently depending on temperature. A steel rod in solid phase gets bigger with increasing temperature, water becomes about 10% larger when the temperature goes below zero and it changes phase to ice. So there's probably no simple correlation in a complex material like wood. I wouldn't be surprised if frozen wood shrinks when it thaws.

The correlation is highly linear as long as you don't involve freezing and drying as this depends on the amount of water. The coefficient of linear expansion is solely dependent on temperature and varies, as mentioned, between different fiber directions where it is smallest in the longitudinal direction. The variation is between 0.5-3 mm/mK

 

[AskeHolst]

The relationship is highly linear as long as you don't involve freezing and drying since this depends on the water content.

But since the OP's question is about frozen timber being thawed, isn't it unreasonable not to account for freezing?

 

[Charley1968]

I've now checked the wood I bought yesterday: it has shrunk by about 0.5%. Interesting. I expected it to swell.

 

[falkn]

I don't mean that the total expansion/contraction results in the wood increasing in size, rather I mean that the two processes should be distinguished. As I wrote in the first post, it will expand because it becomes warmer, but shrink because the moisture dries out, provided that it is actually moist to begin with. If it has been outside for a longer time now in winter when it's dry, it doesn't accumulate particularly large amounts of moisture. Even though the relative humidity is high, the amount of moisture (g/m3) is very small.