Solid timber tables and outdoor garden furniture

Will my timber shrink or warp ? This is one of the most common questions we are asked.

There is a short answer and then there is the attached data sheet obtained from a NSW government department for the detailed long answer.

In simple terms lets divide this into 2 groups: There is fresh timber and seasoned timber.

1. Fresh timber is sometimes called "green" timber or "raw" or even "new" timber

2. Seasoned timber is referred to as "dried" or "kiln dried" or abbreviated to "KD"

The simplistic black and white answers are as follows, but there are shades of grey.

Fresh timber will always shrink. The degree to which it shrinks, cracks and the amount of warping is related to the timber type and the speed at which it dries.

Seasoned timber will not shrink warp or twist.

The shades of grey answers are a bit more informative.

In summary, fresh timber cut from the forest can have upwards of 50% water moisture content and as it dries to the moisture content of the air around us (approx 12%) it will deform, shrink, crack and become lighter. The more rapid this process is, the more profound the impacts can be. Add to this the fact that various timbers have various amounts of moisture to start with, you then have a complex system of drying and shrinkage that is dependent on both timber type and the rate of drying.

Timber that has reached an equilibrium with the surroundings will shrink/expand over the summer/winter season as the moisture levels change. However this is a very small change relative to its first transformation from fresh to seasoned.

OK the obvious exceptions : take a piece of seasoned timber and leave it in the sun over a hot summer day, yes it will bend, but that's more to do with heat on one side than moisture content.


Caring for timber products made from fresh new sleepers:

Where possible furniture made from fresh timber should be allowed to dry as slowly as possible to minimise the affects of ununiformed drying and shrinkage. eg.. key it in the shade over the first summer where possible.

Do not expose the timber to direct heat as this will accelerate the drying process
Do not leave the timber in direct sunlight
Do not store the timber in excessively dry areas
Do not store the timber in excessively windy areas
Seal the timber to reduce the rate of moisture loss
Seal all surfaces to ensure equal drying

The furniture we make is made from : (in order of most stable to least)

Timber type Category Stability
Merbau Seasoned Excellent 10/10
Vic Ash and Tas Oak Seasoned Very good 9/10
Recycled railway sleepers Seasoned Excellent 9/10
Treated Pine F7 Kiln dried Seasoned Very good 8/10
Radiata Pine Seasoned Very good 8/10
Cypress pine sleepers Fresh Below average 4/10
Treated pine sleepers Fresh Below average 3/10
Ironbark/Greygum sleepers Fresh Poor 2/10
Red gum sleepers Fresh Poor 2/10

For a more detailed explanation please read the linked data sheet on seasoning of timber and its affects. Extract from Forestry Commission of New South Wales

Another important metric when choosing timber is its durability outdoors and exposed to the weather. The table then looks like this :

Timber in order of outdoor durability :

Timber type Category Durability
Ironbark/Greygum sleepers Fresh Excellent 10/10
Cypress pine Fresh Excellent 10/10
Treated pine sleepers H4 Fresh Excellent 9/10
Recycled railway sleepers Seasoned Very good 8/10
Red gum sleepers Fresh Very good 8/10
Treated Pine F7 Kiln dried H3 Seasoned Very good 7/10
Merbau Seasoned Very good 7/10
Vic Ash and Tas Oak Seasoned Poor 2/10
Radiata Pine Seasoned Poor 1/10

This is even more important for timbers that are in contact with the ground.
(that is why we use H4 treated pine leg post in conjunction with F7 KD treated pine table tops and seats for our treated pine picnic tables. A perfect mix of durability and stability where it counts)

Timber type Weight per cubic meter
Ironbark/Greygum sleepers 1105 kg dry, 1270 kg wet
Cypress pine 500 kg
Treated pine sleepers H4 700-1100 kg (dryish-wet)
Recycled railway sleepers 950 kg
Red gum sleepers 900 kg
Treated Pine F7 Kiln dried H3 510-580 kg
Merbau 850 kg
Vic Ash and Tas Oak 620 kg
Radiata Pine 400 kg

Large 'E' profile picnic table : 260kg in Ironbark and 125kg in Treated Pine !

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