Moisture – How it Affects the Timber Resource of Today

A homeowner recently experienced significant board expansion on their Jarrah tongue & groove floorboards. The boards had expanded and humped up, causing an S shape in the floor. 

However, this was not the worst case I have seen. There was one job I inspected where the Jarrah floorboards humped up about 200 millimetres.

So, is this a result of the timber specie or poor installation?

Many builders have installed veranda floors that have performed well and more importantly, stood the test of time. Recently, I inspected a few jobs where the floorboards had buckled and each time, the builder reassured me they acclimatised the flooring and never had a problem until now.

The question is: why has the same specie/product worked well in the past but is causing issues today?

Due to government regulation, virtually all old-growth forests have been protected by logging because of environmental issues. This limits the industry to harvesting shorter re-growth logs. This is problematic because not only is the wood less mature, the percentage of sapwood within it is higher. The sapwood is invariably more reactive to moisture content changes than the inner part of the tree called the heartwood. This in turn affects the durability of the timber towards moisture and has no doubt, contributed to some of the recent floor problems I have attended.

“Due to government regulation, virtually all old-growth forests have been protected by logging because of environmental issues. This limits the industry to harvesting shorter re-growth logs.”

Another important factor is the quality control of timber manufacturers. Most timber manufacturers have sophisticated technology that allows them to acclimatise their products before they are distributed to retailers. The timber is typically dried to the Equilibrium Moisture Content (EMC) of Australia’s two major markets: Melbourne & Sydney.

This means that builders do not need to acclimatize their floorboards unless the timber is being installed in an area with drastically different weather conditions. 

For example, acclimatizing in the winter months could increase the moisture content, so it will likely shrink in summer. The opposite can apply in the summer months. Installing floorboards as close as possible to their “lived conditions” is therefore essential.

If you are building a veranda floor, our recommendation would be as below:

• Use Merbau Flooring as it has much less expansion/shrinking qualities than Jarrah
• Coat the product with timber oil on all sides to help prevent moisture ingression
• When installing the boards, allow a small expansion gap between boards
• Top fix the Veranda flooring

If you are unsure on whether you should acclimatise your flooring before installation, or have any queries, please do not hesitate to contact me via email: [email protected].