Indeed moisture in all its forms is without a doubt the most influential and perhaps the most underestimated, destructive and damaging element in a timber flooring project, and it can have a profound effect on all of the components that make up an installation.

A broader understanding of the nature of moisture ingress and the impact it can have on coatings, adhesives, timbers, and foundations is essential to ensuring the long-term stability of a timber flooring installation.

The cooler wet months of the year and periods of high humidity often cause delays for floor finishers and installers. At the onset of winter a friend of mine in the timber coating industry would hang a poster on the notice board at the businesses he visited. The purpose of the illustration, which depicted washing hanging limply on a clothes line and the associated caption, was to remind the tradesmen that coatings – like clothing – take longer to dry in cold or damp conditions.

In cold weather, the viscosity of many coatings increases as humidity rises and temperatures drop, resulting in longer open times, extended periods between coats and an increased risk of quilting and the “╦ťorange peel’ effect (which happens when the solvent evaporates before the solids in the solution have had time to spread evenly over the timber surface).

Cold weather conditions can also affect the sheen level of the coating, so when the dew point temperature is reached, the water vapour contained in the air will condense into a liquid – and the resulting moisture particles settle on the coating surface – causing it to appear cloudy or dull.

To counteract some of the negative effects, coatings have to be within a specific working range. For most coatings this is somewhere between 16 to 30 c and 40 to 80 per cent relative humidity (RH) with the ideal figures being 25 c at 60 per cent RH.

Timber flooring products – like their coating counterparts – are susceptible to humidity and the prevailing weather conditions, hence, the importance of acclimatising timber to the conditions expected in order to prevail in the service area.

The process of acclimatisation requires that the timber flooring to be “╦ťstacked’ in the intended installation area, until the moisture content of the timber is within + or – 2 per cent of the equilibrium moisture content (EMC) of the microclimate for the proposed service area (AS/NZ 1080.1). This can be a time consuming exercise, often complicated by the effects of surface water and subsoil moisture.

Ideally, surface water on building sites and established properties should be directed away from the exposed edges of foundations and footings to stop or minimise moisture ingress.

Slab edge dampness occurs when water breaches the unprotected edge of a concrete foundation, forming a moist band in the concrete perimeter extending 300 mm to 600 mm within the room. The entrapped moisture is drawn upward through capillaries in the concrete, leaving behind crystallised minerals as it exits as vapour at the slab surface.

Crystal residue or efflorescence is often the first sign of slab edge dampness. If left unaddressed, the crystal will continue to expand causing the concrete to break down, which can result in a moisture barrier and adhesive failure at the bond line. The flow-on effect of this is likely to include cupping in the boards, drummy spots, and localised lifting of individual boards around the perimeter of the installation.

The presence of slab edge dampness may not be evident to the flooring contractor at the time of a site evaluation or installation, as the time between building development and the onset of slab edge dampness can vary greatly due to construction issues or changing conditions in the life cycle of the building. This being the case, both old and new buildings are vulnerable to slab edge dampness.

Moisture or water build up in subfloor spaces will result in cupping or doming of the overlying timber and long-term exposure to excess moisture in humid conditions will promote mould growth (causing a general darkening of the timber or blackening within the grain as rot sets in). Dark, damp spaces have also been known to attract termites.

Geographic positioning is known to influence and contribute to the impact of moisture on any given installation site, particularly in the case of sub-soil water or moisture. Subsoil is the layer of soil underneath topsoil and is made up of a mixture of sand, silt and clay.

Site geography, whether it is positioned on a slope or flat, should guide the design of foundations and footings in order to divert moisture away from the structures. This is especially the case when a site is cut in for development purposes.

Moisture will find a path through the sub-soil via the easiest route, passing freely through porous materials like sand, silt, or fissures caused by seasonal soil movement and decaying tree roots. Its course will deviate, or the moisture will pool when faced with more viscous material like clay, foundation footings and piers.

If the water is unable to find an alternate escape route it will rise to the surface as water or vapour, depending on the amount of ground water at any given time and the temperature changes in the soil.

When this moisture emerges under concrete slabs or around footings and in sub-floor spaces, the effect and resulting problems are similar to those noted for surface water (slab edge dampness and timber decay).

A friend of a friend once purchased an older property in the inner city, and during her first winter period in the home the floors began to squeak and become uneven (cupped).

I was called in to look at the problem, only to find that her cellar had become an indoor swimming pool. The cellar was cut into the subsoil, which flooded when seasonal rains caused an increase in subsoil moisture.

Preventing moisture related problems in timber floors may be impossible, but minimising them is as simple as taking a holistic approach, which should be implemented from the very beginning when measuring the job or assessing the site.

The timber flooring industry might describe moisture in its many guises as a nuisance at best, and a nightmare at all other times.

However, from the forest to the floor, moisture is a crucial element in the successful life cycle of a piece of wood, with both the power to nurture – and destroy – our most valuable building material.