July 3, 2018

Plywood Moisture Content: A Primer

The moisture content of plywood is a key parameter that determines its quality. If the plywood is too dry - i.e. the moisture content is lower than the optimum level - then it leads to the plywood becoming weak. However, if the moisture level in the plywood is too high, it is likely to result in rot and decay in the plywood in the future. Hence, the moisture content in plywood needs to be balanced.

Optimum Levels of Moisture

According to the Indian standards specification IS:303, the moisture content in plywood should ideally be in the 5 - 15% range. At PEEL Ply, the moisture level in the plywood is carefully controlled within the 8 - 12% range, no matter in which part of the country the testing is done or at which time of year. This ensures that you - the end customer - reap all the benefits of plywood that is ideal in its moisture content.

Benefits of Plywood with Optimum Moisture Content

Keeping the moisture content of plywood within the prescribed range has various benefits, the key among which are:

• Production of a quality product which doesn’t split, bend or warp
• Production of plywood that displays increased strength compared to drier plywood

Production costs and productivity also see movement in a favourable direction when the plywood being produced has an optimum level of moisture.

Reducing the Moisture Content in Wood: How it’s Done

Plywood is essentially composed of several alternating layers of veneers or thin slices of wood which are pressed over one another and glued together with an adhesive. Now, the proper glueing of these slices of wood or veneers is not possible unless the veneers contain less than 10% moisture.

During the manufacturing process, the veneers are first cut and then dried using mechanical drying processes in order to reduce the moisture content of the wood. This is done by passing the veneers through hot ovens or mechanical dryers on belts moved by rollers. Simultaneously, fans circulate the hot air generated by the coils of the oven over the surface of the veneers in order to finish the drying process. Once it is complete, that is, once the veneers are dry enough, they are stacked one on top of the other and not just glued but, in fact, bonded together i.e. glued under high temperature and pressure in order to make sheets of plywood.

Determining the Moisture Content of Plywood

The moisture content of plywood can be checked using simple hand-held devices such as moisture meters, which are available in both digital and analog versions. Their working is similar to that of a resistance meter. To elaborate, two pins inserted into the plywood establish an electrical current between them with the help of the moisture content in the plywood and a battery-powered meter. The meter then calculates the resistance to the flow of the current, which it displays in terms of the moisture content of the plywood.