by Locke Wilde
1. Preparation: Be sure that both surfaces are clean and free of dust. Clean the back of the veneer sheet as well as the substrate with air pressure and wipe down with denatured alcohol (do not flood). The sheet veneer and the substrate should be acclimatized together for at least 24 hours (48 hours is best) before bonding.
2. Adhesive: In most shops, the adhesive of choice is contact cement. This is not necessarily the best, but it is the easiest to use. The adhesive you choose is the insurance policy on your work. In the eyes of your customer, if the glue fails, you fail.
Remember that contact cement is a flexible adhesive designed to glue a rigid overlay, such as plastic laminate. With sheet veneer, you are using a flexible adhesive to glue a flexible overlay. Because of this, you must use a different method of application.
A) Always use 100% coverage on both the back of the veneer sheet and the face of the substrate. As a rule, use twice as much adhesive as you would when gluing plastic laminate.
B) Give the adhesive the right amount of dry down time. You don抰 want to trap gases that can later cause blisters. The time can vary depending on ambient moisture, airflow around your work area, and ambient temperature. Check with your adhesive supplier to find the dry down time that is right for your conditions and the adhesive you are using.
C) If possible, use a PVA (yellow or white glue) or a urea resin in a press for the best bond.
3. Bonding: Bonding is the second most important part of your job. The desired bond makes two pieces one. It is reached with the proper amount of adhesive and pressure. You can apply a lot of pressure all at one time (using a wood scraper) or consistent pressure over a long period of time (using a vacuum press).
With contact adhesive, you will need a lot of pressure all at one time. You can buy or make your own wood scraper, which should be 4-5 inches wide. Starting in the center of the surface to be bonded, pull the scraper in the direction of the grain. Push down with both hands, as hard as possible, moving over 3 - 4 inches at a time until you have covered the entire surface.
To quote a speaker at the Wood & Wood Products Veneer Seminar in 1998, 揑f you are not wet with sweat when you finish scraping down a sheet veneer job, then you didn抰 apply enough pressure.?
Do not use a J-roller to apply sheet veneer梚t will not apply enough pressure to make an intimate bond. This is one point on which all sheet veneer manufacturers agree. A J-roller will void your warranty if used on sheet veneer. Using a J-roller can result in a series of blisters every 16 - 20 inches when trying to roll out a full sheet of veneer or a large conference table. This is the distance at which the point of pressure is lost due to the extension of your arms.
4. Time: After you have bonded the sheet veneer to the substrate, allow the piece to sit. In order for contact cement to work, a chemical reaction must take place. This reaction produces gas, which must escape from the edges and surface before the seal coat is applied. Wait at least 4 - 6 hours before applying any sealers or finishes to a veneered surface.
5. Finishing: You have taken two products (sheet veneer and substrate) and by bonding, formed them into one. You have used two products with the tendency to expand and contract and bonded them with a flexible adhesive (contact cement). Now, in the finishing process, you will be applying a liquid.
When you begin your finishing process, remember this: Wood moves when moisture is added to or taken away from.
Be sure to apply the sealer in stages. A sealer coat sprayed in a very fine mist often works with great success. Don抰 flood the wood surface all in one coat. When you apply a heavy amount of liquid over sheet veneer glued with contact cement, you risk movement and ultimately cracking or blistering in the finish. The following causes this:
A) Not enough adhesive was used.
B) Not enough pressure was applied to form an intimate bond.
C) The finish was rushed and gas from the adhesive was not allowed to flash off.
I hope these hints help you to make a better product. Until we talk, Good Veneering!
This article outlines the proper procedure for sheet veneer installation as expressed by C. Locke Wilde, National Sales Manager of Jacaranda, Inc., and others throughout the industry.