‘Moving’ and moisture

Q: I am considering using Western Australian karri as a solid timber floor. I have heard conflicting reports that karri ‘moves’ a lot more that other similar timbers (e.g. Sydney blue gum, jarrah).

ANSWER:

When we talk about timber products ‘moving’ we are referring to the swelling (or shrinkage) that takes place with a change in moisture content. If there is little or no change in moisture content, there is little or no shrinkage. Timber responds slowly to changes in atmospheric humidity, particularly if it’s sealed, so if there are a couple of dry days followed by a couple of wet or humid days, there probably won’t be any movement at all. If there is a prolonged period of dry or damp weather, it’s true that karri moves slightly more than some other timbers, but the difference is small. Australian Standards quote movement figures of 0.3% of the width of the board, per 1% change in moisture content for jarrah, 0.35% for Sydney blue gum, and 0.4% for karri. This means if there is a 2% change in moisture content from summer to winter, a 100-mm-wide karri floorboard is likely to ‘move’ by up to 2 x 0.4% x 100 mm = 0.8 mm. The most important thing is to ensure the moisture content is suitable for the situation. For most of the southern parts of Australia, that should be 10% to 12%, but this may vary by location. Your timber supplier and/or installer should be able to do random checks with a moisture meter to confirm the timber is in the right range.

Timber reacts to changes in moisture

Timber reacts to changes in moisture content