I'm having trouble getting rid of a few bubbles in some rift sawn oak veneer (paper backed) which was applied to veneer core plywood. I put two coats of Weldwood contact cement on both surfaces before applying, but a few bubbles are appearing. The veneer was somewhat wavy in places before I started the job. Applying pressure on the bubbles eliminates them temporarily, but they reappear after an hour or so. What can I do?
Your two coats of contact might be part of the trouble. The waviness is part of the sheet veneer and should not be causing the blisters. The waviness is from the grain of the oak drawing moisture from the air.
The blisters could be a combination of things:
1. Possibly a build up of too much adhesive. (Hard to tell without seeing the face or how it was applied).
2. Not enough open time.
3. Not enough pressure. (You did not state what type of pressure you used).
Tools needed: iron, felt cloth, wood scraper, sewing needle (large) and heat sink.
1. With the needle, put a hole at the top and the bottom of each blister. Make sure to go through the veneer backer.
2. Taking an iron with the setting between cotton and wool, or 190 degrees, heat up the area all the way through to the adhesive. You said there is no finish applied, but you don't want to burn the wood face.
2. Use a piece of felt (from K-Mart) or a heavy piece of craft paper. Make an outline of the blisters on the face of the cloth. The cloth should be a least 18" to 24" square.
3. Cover the blistered area and start to warm up. Keep the iron moving in a circular motion until hot, about 10 minutes.
4. After bringing up to heat, remove the cloth and apply pressure with the wood scraper to the blister area, forcing the air toward the two holes you made going with the grain. Repeat if needed--it could take up to 2 or 3 times to properly lay down.
5. This is the part that will make it all work. You need to take away the heat as fast as you can so the contact will reset and not stay soft and give way again. One of the best heat sinks is a small, smooth-bottom aluminum frying pan. Rub the pan over the area that has been heated. As the pan gets hot, cool it down by applying denatured alcohol (this will not leave a watermark on the wood face as it dries). Repeat several times until the surface is cool.
6. Take a clean, lint-free cloth and wipe down the entire face with denatured alcohol. Let set a minimum of 4 hours.
8. Finish. When you start to apply your finish, remember that this face will want to move again, as all wood does when moisture is added to or taken from it. Do not apply a heavy coat of anything all at once. If lacquer is your finish of choice, think about using a barrier coat before applying your first coat.
Locke Wilde, forum technical advisor