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[Industry Knowledge] About Veneers

About Veneers

The Process

Veneer starts out as a log that has been carefully selected and processed. Green logs cannot be sliced because dry logs are too brittle. All logs or log pieces must be soaked in hot water so that even the internal fibers are moist enough to be sliced. They are soaked in approximately 70 degree Centigrade water until the are almost so heavy they will not float. The vats are then drained and the logs or pieces of the logs are cleaned. They are then ready to be put on a lathe or slicing machine and sliced.

Types of Veneer Slicing
There are three main types of veneer slicing equipment used commercially —

rotary lathe in which the wood is turned against a very sharp blade and peeled off in one continuous or semi-continuous roll

slicing machine in which the flitch or piece of log is raised and lowered against the blade and slices of the log are made

half round lathe in which the log or piece of log can be turned and moved in such a way to expose the most interesting part of the grain.

Each of these types of processes gives a very distinctive type of grain depending upon the species. In any of these veneer slicing methods, when the veneer is sliced a distortion of the grain occurs. The knife blade as it hits the wood creates a "loose" side where the cells have been opened up by the blade, and a "tight" side. The coloring differentiations created by the tight and loose side should not be confused with the "barber poling" effect which takes place in certain wood in which the same piece of wood appears to be dark or light depending on the way it is viewed. This is caused by polarization of the grain wherein the grain is slightly angled from the surface, and depending upon where the light source is coming from, the grain is either in shadow or is penetrated by the light.

After the veneer is sliced, the veneer passes through a drying kiln to bring its moisture content down to approximately 8%. Upon exiting the dryer, bundles of veneer are made from sequences of veneer leaves. Bundles generally include 24 to 32 leaves.
Specifying Veneer

Your choice of materials and how those materials are used are decisions you will make during the design process. When choosing veneers, here are some key things to keep in mind:

Selection of Quality Grade
Architectural Woodwork Quality Standards Illustrated, published by AWI, provides three levels of quality: custom, premium and economy. Each quality grade has direct implications in the defects permitted in the veneer and the quality of the panel products. The Quality Standards also describes the method of gluing, splicing, sanding and backing panel products.

Selection of Veneer Species
Veneer species and method of slicing of the face and the back of all panel products should be specified. It is best that this information be either in the specifications or on the drawings, but not in both locations. Many problems can arise when a specification is not updated after the drawings have been revised. It is not unusual to find a specification calling for rift red oak when the design drawings indicate another species, such as walnut. This leaves the woodworker unclear on what to bid and the design professional with a potential liability for additional costs.

Selection of Core Type
Consideration should be given to special requirements such as fire resistance, water resistance, weight, flatness, rigidity and strength required, defining the core which best fits a project's needs.

Selection of Veneer Matching
There are three areas of consideration with respect to veneers, all of which have been termed "matching." It should be understood that these are very different considerations. Confusion can sometimes result because of the use of the single word, "matching," to describe these considerations. The three types of matching are:

o Matching between veneer leaves: deciding between slip, book, random and reverse slip match.
o Matching within the panel face: deciding between an unbalanced, balanced, center balanced and unmatched face.
o Matching between panels: deciding if adjacent panels are to match, and if so to what degree.

Source: Hanbao

Posted and edited by Ran, Hanbao News Department