Tape Issues when Joining Veneer

Veneer tape can cause minor defects at the seam. Here are some suggestions for preventing that problem. March 31, 2008

I'm working on a maple veneered vanity for customer. After applying the moistened veneer tape, the pieces started to curl. They come out of the cauls flat, but I was left with a groove down the seam line (like the scratch a coarse grit makes). What caused this? I am not sure if sanding will take it out. Is using a low tack tape better than using the veneer tape? I've only veneered once before, so this is an education for me.

Forum Responses
(Veneer Forum)
From John Van Brussel, forum technical advisor:
What type of glue did you press with?

From the original questioner:
I used a urea based glue from Constantines - 7 parts liquid to 1 part powder.

From John Van Brussel, forum technical advisor:
I think your glue mix ratio is incorrect. Usually mix for urea based glues is 100 parts powder by weight to 50-65 parts water by weight.

From contributor T:
I have the same problem when joining veneers, especially maple veneer. The wet tape causes the edges to curl so much that the joint is compromised while pressing. There are two solutions. One is to also wet the backside of the seam. Two is to scrap the wet tape and use Scotch tape. Press it on firmly with a roller. This is all I use now. No curling, no ghosting, no washing off residue. Cheap tapes are useless (don't stick), hence I like 3M's Scotch brand. Other guys like specific brands of clear packing tape. Try different brands for yourself. Cellophane is used by the British but no one seems to make it specifically for veneers. This baffles me. I hate the paper stuff.

From contributor J:
I agree with contributor T's diagnosis of your problem. I have switched from using veneer tape to using blue "safe release" masking tape from 3M. It has excellent holding power. You can just put it on with finger pressure, and it removes very easily as well, as long as you don't let it stay on for more than a few days.

From contributor N:
Regarding using blue painters tape for joining veneer, I have heard of this method but been reluctant to use it because of the thickness of the blue tape. Do you find that the thickness of the tape does not cause a problem? Also, I have been unsatisfied with the joints I am getting in my veneer. How do you get a perfectly straight and smooth joint between pieces of veneer? Do you get your veneer perfectly flat before you joint or rout the straight edges?

From John Van Brussel, forum technical advisor:
Blue long mask tape is usually used to assemble a face temporarily. The face is then flipped over and gum taped. Flipped again and the blue tape removed. This becomes the glue side. After press the gum tape is removed by various methods, i.e. scraping, sanding, dampening with hot water.

The masking tape could work if you were vacuum pressing but most guys I talk to still get fiber pull when they remove the masking tape. I would not use it in a hot press application.

Regarding jointing of the veneer, we now offer a couple of jigs which can be used with common shop tools to achieve an excellent joint. There is one for a table saw, sliding table saw and circular saw.