Why does wood need to be dried before made into products?

- Apr 10, 2019-


drying wood

When wood is cut from a living tree, it is saturated with moisture. Water makes the wood easy to grow mildew, change color decay and damaged by insects. If the wood without drying is made into wood products, the products will contract deform and even crack, due to the differing shapes and sizes of the wood's cells. Therefore, wood needs to be dried thoroughly before used.

 

Generally wood after drying will have advantage as bellows:

1) Better usability. Wood shrinks as it loses moisture and swells as it gains moisture. It should be dried to the % MC it will have during use.

2) Reduced shipping costs. Dry wood weighs less (drying may reduce its weight by one-half or more). It is more profitable to transport wood than water.

3) Less likelihood of stain or decay during transit, storage, and use.

4) Reduced susceptibility to insect damage.

5) Increased strength. As wood dries below 30% MC, most strength properties increase.

6) Better “hold.” Nails, screws, and glue can be hold better in seasoned wood.

7) Better finishing. Paints and finishes adhere better to seasoned wood.

8) Better heat insulation. Dry wood is a better thermal insulator than wet wood.

9) Better preservation. Dry wood must be used when treating with most wood preservatives.

10) Added value. Drying the wood products before shipment adds value to the product.

 

Drying methods

There are two main methods for wood drying

Drying naturally

The wood is placed in a well-ventilated shed to avoid direct sunlight and rain. Through natural convection in the air, the moisture in the wood is evaporated and balanced. This method is simple, low-cost, time-consuming and easy to give rise to insect damage and decay.

Artificial drying, including Dipping Drying, Steaming Drying and Kiln Drying

1)     Dipping Drying is to dip the wet wood in the flowing water for 2-5 months in order to get rid of the liquid part of the wood, and then air-dry or steam-dry the wood. This method can reduce the deformation of the wood, save time than drying naturally, but the strength of the wood decreases.

2)     Steaming Drying is to steam the wet wood with hot steam first, and then dry it naturally. This method can speed up drying, have insecticidal and sterilizing effect but the elasticity, strength and luster of the wood are reduced.

3)     Kiln Drying is to Dry wood in an insulated chamber and circulating air over it. This method can make high-quality dried wood efficiently.