Wicking

Imagine putting up beautiful, pine clapboard, staining it and the, ten years later, there is rot underneath. This happens very often in clapboard siding and it is called "wicking."

In the same manner that dry sponges and paper towels soak up moisture water will be drawn by capillary action up in between two tight pieces of wood and, because there is no room for airflow, the wood will stay wet and begin to decompose from the inside out.

The key to stopping the wicking action is to get some inert spacer between the wooden surfaces. This can even be an air space.

When building a deck, for example, it is easy for the joint between decking and the joist to be subject to wicking. Many carpenters will cover the joist end with tar paper or thin white foam which will not only stop wicking it will direct the water away from the wood.

Manufactured wood siding has a back that is grooved to allow water to drain out and air to get in and dry out any moisture. This is called "rabbeting" and the success rate for this new design is almost 100% when installed correctly.