Troubleshooting Veneer Tape Ghosting

Fine points of taping veneer joints, to avoid visual defects. October 14, 2006

I am having a couple of issues with veneering on some work we are doing. One is a slight ghosting of the veneer tape when we tape our joints together. After we remove the tape, it appears to have slightly sealed the wood so that when you stain it, you can see the pattern of where it used to be. The other problem is some wrinkled veneer that we have to flatten. Is there a simple way to flatten it so that it can be glued to a substrate?

Forum Responses
(Veneer Forum)
From contributor T:
Stop using surface tape. Use a zigzag string application device applied to the underside. Try relaxer to get rid of the waves. Vacuum press or lam bag will help with quality.

From contributor J:
Since tape is a necessary tool in any shop that works with veneer (whether they have a stitcher or not), let's try to solve your tape problem. Can you give us a really detailed outline of your process? Have you had this problem with other flitches of veneer as well?

Regarding flattening: I'm aware of two types of flattener. One is a glycerin-based flattener that you can make up yourself - search the Knowledge Base here at WOODWEB for the formula. The other is GF-20, which I believe is PEG-based (not certain). I get it from Veneer Systems, Inc. I like it better.

From contributor E:
If only veneering was a science!

Tape Ghosting - The usual suspects:
Is this happening on species that are subject to tone changes with UV exposure?

Could it be that you have hard water and are seeing mineral deposits? Try distilled water.

Has the face maker changed and maybe a new guy is using more water than previously? Excessive water on the tape can cause grain deformation. The adhesive thins out too much, leeches into the grain, and shows itself (normally at finishing).

Have you changed the tape removal process?

Have you changed from vegetable to animal adhesive?

Has anything changed with regards to your normal process? New tape dispenser, changes in how you press, did you change adhesives, etc.?

From contributor F:
Could it be that the veneer tape's adhesive is not being totally removed from the work and this residue is preventing the stain from penetrating fully at the veneer joints?

From contributor W:
I am really careful about this problem after having experienced it myself. I scrub the taped areas with a rag and warm water after peeling up the tape, using a cabinet scraper as well. Then I wash the overall surface, both to remove any remaining residue and to reveal any unglued areas, which show up as bubbles, or hopefully not. Wait at least 24 hours after pressing for glue to fully cure before washing, leaving panels on edge to air-dry. I recently stopped using an aluminum pot for the wash water, as it caused fine black specks on Douglas fir veneer which did not sand out. Hard water could also discolor some woods. Use a raking light when sanding, as some areas may still have tape adhesive ghosts, which should be sandable.

On the subject of zigzag stitching in the glue line, I have seen too-thin veneers sand through in a zigzag pattern because the threads cause minute bumps in the face, a defect worse than tape ghosts. I like tape!

From the original questioner:
What do you mean by a raking light? I have not heard of this term.

From contributor W:
By raking light, I mean a strong light placed low over the surface and behind the work. This reveals the reflectance which tells you where the glue has not been fully cleaned off, and highlights any bubbles.