Finishing Timber Veneers
The need for finishing
Veneers like most timbers used in furniture, joinery and fit-out require a protective coating or lacquer to protect them from the rigours of day to day usage. It is important that the selection of finish is suitable for the end use application of the finished piece of furniture, etc. For example, a highly decorative jewellery box doesn’t need the same durable coating as a kitchen cabinet, or even a laboratory fitment does.
Selection of Veneer and Substrate
Veneer selection is essentially a design issue. There are finishes available for every veneer and timber although some need more careful treatment than others.
Substrate selection is also fairly open although it is highly recommended that moisture resistant boards be used in high humidity areas or areas subjected to occasional wetting. e.g. Bars, kitchens, etc.
Inspection and Preparation
The most critical aspect of preparation is the control of moisture content of veneered boards. High moisture content is difficult to detect visually (unless it has progressed to “puffiness”) so prevention is the key. Do not leave boards exposed to wet or humid conditions. Particleboard and MDF both pick up moisture from the air so store in a cool dry place.
Veneered Boards should be sanded smooth. Care should be taken to round sharp edges since finishes (especially viscous liquids) tend to draw away from sharp edges and minimise the seal. A well lit workplace is essential to ensure that the piece to be finished is free from marks, indentations, etc., that will detract from it’s appearance.
After sanding ensure that the board is clean. Dust and grit will adversely affect finish and care should be taken to remove loose particles before installation.
Oil, wax and other contaminants also need to be removed before a lacquer is applied. If necessary use a grease remover.
An appropriate face mask should be used when spray-painting to prevent solids i.e. spray mist from entering the lungs.
Treatments vary markedly with desired finishes and products and it is important to follow the manufacturer’s instructions carefully. Short cuts can cause problems which can take weeks or months to show up. It is recommended that products and methods used be recorded for each job which will provide useful information on the cause of problems should they arise.
The other issue is the environment – temperature and humidity can affect the finish. Finishes should be applied in controlled environmental conditions, out of draughts, away from dust, moisture and other contaminants.
The back or reverse side of all panels should be sealed to slow and equalise the ingress of moisture. Panels not sealed in this manner may bow or cup.
Selection of Coating
The following table provides some guidelines for coating selection. Remember a high quality lacquer will help achieve a high quality result. Cheaper finishes usually have lower solids contents and take more coats to achieve the same finish. You also need to consider the grain of the veneer – open grained veneers may require filling (especially if a gloss finish is desired) or a more flexible lacquer. The use of ‘thin wet’ coats and the addition of solvent can be helpful.
Some species of timbers (and veneers) have phenols, tannins and other chemicals present in their cell structure, these species are best sealed with a specially formulated ‘isolator’ coating that provides a barrier to stop the chemicals in the wood reacting with the chemicals in the top-coat. Lacquer manufacturers can provide advice as to the most suitable coating system for particular species.
It may be necessary or possible to use two or more coating systems on a piece of furniture. For example, a dresser or sideboard needs a very durable serving surface, whilst the vertical surfaces can have a less durable, but just as attractive coating. Oil type finishes, generally known as ‘Scandinavian Oils’ should be applied over a quality sealer or lacquer. Application of oil type finishes to veneered surfaces may adversely affect the bond of the veneer to the substrate and/or the surface appearance.
Note: Under no circumstances should two pack products be put over single pack coatings. Where an acid catalysed sealer is unavailable a polyurethane sealer is recommended.
Manufacturers of furniture, joinery and fit-out should provide instructions as to the ongoing, in service, care of the finished article. As these instructions now largely apply to the treatment and protection of the surface finish, they should be formulated in conjunction with the lacquer supplier.
If problems are encountered with finishes applied to veneer, a questionnaire is available from AFRDI/Furntech (03 6326 6155) which will help develop our understanding of the causes and assist with educating the industry. Any information collected will be treated in confidence.
Provided by AFRDI/Furntech (the Australasian Furnishing Research & Development Institute) with assistance from CSIRO and Mirotone and edited by Grahame Waterson.
Every attempt has been made to ensure the accuracy of the information contained in the Veneer Product Information Manual, the Decorative Wood Veneers Association does not accept responsibility for any loss or damage which may be sustained by a party from reliance on the information contained herein.
Coating Systems Selection Guide
Timber and Composites
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