Preventing veneer from expanding and buckling through proper gluing and application methods. November 7, 2000
Why might veneer expand after 3 months of being finished and installed? In several places where the veneer comes together it seems as though it is pushing up at the seams. The contact glue used is the green from Wilsonart. I've had the finish checked with a dry mill gauge and it's okay. It is random, and occurs on mdf and ply, but mostly mdf.
I have found out that when using contact cement a minimum of two coats on each surface is required. Let it dry between each coat. Then apply the veneer to the substrate. Iron on the veneer and then drag a veneer hammer or some other type of pressure device over the surface with as much pressure as possible.
I let it sit over night before trimming because it does grow or creep. In most cases that holds and it seems to be stable.
If that doesn't work use a resin glue on it, but that takes hours to dry. You need clamping or a vacuum system for that. I have also used yellow glue and ironed it on, but I find that creeps also. I did a 10 foot by 30 inch counter top for a credenza with mahogany veneer and I used the resin glue on that under vacuum. It looked like one large board when it was done.
Whenever you use contact cement with veneers there is a risk of delamination because of the finish solvents attacking the cement. I solved that problem for myself by buying a vacuum press. The glue I use with this is a Unibond 800 (207-725-0935), which is a two part Urea Formaldahyde. It takes a long time to cure but this would solve your problems in the future.
Contact was designed and invented for plastic laminate. It is flexible and designed to glue down a ridge product. When the woodworker took contact adhesive (a flexible glue line) and said let's lay sheet veneer, it all started.
Flexible sheet veneer was designed to be applied with a ridge glue line and a press. The manufacturers found out in a hurry that not enough woodworkers had a press or wanted a press. So the following instructions were agreed upon by most of the flexible sheet veneer manufacturers.
1. Both surfaces shall be free of all dust before applying contact.
2. Contact adhesive should be applied in a box coat method (applied in both directions).
3. 100% coverage applied to both surfaces (Approximately twice as much as required for plastic laminate).
4. Drying time is very important. Don't trap gases. It is the gases that cause the blister and surface checking. They are a natural process in contact, so it is up to you not to get the gases trapped. If you wait 15 extra minutes now you can save money later.
5. Maximum pressure should be applied by use of a wood scrapper. DO NOT USE A J-ROLLER ON SHEET VENEER. Applying maximum pressure requires work. You are working to get an intimate bond between two foreign products.
6. When one has completed the laminating process the next step is NOT to flood the veneer surface with finish or moisture of any kind. WOOD MOVES WHEN MOISTURE IS APPLIED. A barrier coat of sealer is recommended by a lot of the finishing manufacturers before your finish coats are applied. With the type of finishing you use make sure your first seal coat seals the wood fibers and does not flood the finish.
P.S. When veneer expands because of being flooded with finish, it sometimes takes about 3 to 5 months for the air-conditioner in a home to draw out the moisture. This is when the surface checks and blisters start showing up.
Locke Wilde, forum technical advisor
Buckling is caused by many things. To help eliminate it you can use a 2 part epoxy system like West System and vacuum bag it. It will take about 8 hours to cure. You can also use a polyurethane glue. It is a stand alone glue and you only need to apply it to one side and wipe the other side with a damp cloth before putting it together. You will also have to apply pressure to it to keep it in place until the glue cures. It can also be vacuum bagged.