Q: We have some cherry veneer that looks great when we're working with it, but then when we finish it, wiggly zone patterns appear in the veneer running from side to side (not lengthwise) and they seem to repeat about every 2 to 4 inches, but it's variable. The veneer is smooth, but there are these color patterns. Sometimes we notice that in the book-matched veneer, that the matched piece has the zones offset. Can you tell me what this is or do you need to see a piece?
A: It's common to find that color differences or patterns show up after finishing, but are hard to detect before finishing. This is true for lumber and veneer.
The pattern you describe in veneer can be put into the veneer due to excessive pressure during manufacturing. In sawn veneer, if one tooth is badly miss-set so it scratches the veneer, it will leave a color pattern. If a veneer knife has a chip so it tears rather than cuts fibers, it can leave a scratch that will have a color variation, too.
However, in your case, the fact that the zones are frequent, not evenly spaced and are reversed on the book-matched piece is more likely the result of oscillating grain within the wood. In hard maple, cherry and other species, such oscillations are rare; they are called fiddle-back grain. When the grain oscillates in this manner, sometimes in one small area you're working with end grain and then, in an adjacent area, flat grain. This grain difference causes different stain adsorption and different finish adsorption. Plus, depending on the light angle, you'll get different reflection from the different grain when using a clear finish. If you find this pattern objectionable, you could test finish one piece of veneer from each flitch to make sure that this characteristic isn't present. Some people actually like this pattern and pay extra for it, so you should be able to return the flitches that aren't going to work for you for full credit.
Q: We're having zero success gluing ipe. I'm hoping you can help us.
A: Ipe (pronounced ee-pay) is an extremely dense South American hardwood that's heavier than water, or more than 75 percent denser than red oak. The common name of ipe includes wood from the genus Tabebuis, but there are more than 10 species of wood in this genus that produce lumber called ipe. This means that you'll see some variation in the lumber from time to time.
Being so dense, the wood is indeed difficult to glue. The surfaces to be glued must be perfectly flat and true. The grain is also interlocked at times, which means surfaces will become uneven if there's any moisture change after preparation. But there's another problem with this wood. Ipe has a chemical (called lapacho) that will migrate to the surface over time and will thereby create poor gluing, even with epoxy.
It's best if you consider fastening this wood with screws or nails (predrilling the holes for sure), rather than gluing. But, if you do want to glue the wood, it will glue fairly well if surfaces are freshly prepared (within minutes) and are cleaned with a solvent (acetone, lacquer-thinner; be safe when using these; check safety and environmental procedures) a minute or two before gluing. Of course, all other standard gluing procedures must be followed, which includes avoiding excessive pressure, having enough glue, having flat mating surface, and so on.
Q: I was reading your February 2006 article titled "10 Facts about End Cracking." Your 7th fact stated, "Do not humidify the plant above 37 percent RH." We're a small firm that does architectural, commercial, high-end homes, just about everything. Our humidity is set at 50 percent and we have virtually no callbacks (the only one was a table that was veneered onto plywood as per the customer's wishes). Are we just lucky? Should we be set at 30 to 35 percent as you stated?
A: Some products don't require close moisture control, as a little movement isn't going to cause a defect. Other products, such as table tops, are very sensitive to moisture changes. So, to be safe, I suggest that the RH in your plant mimics the RH in the customer's home or office.
I do wonder how you're able to maintain the high RH in the wintertime. It would take an excellent humidification system. You would likely see a lot of condensation on the windows and other cold spots. So, I ask, "How you are measuring RH?" The brass office instruments and many others are not accurate enough. You can purchase a good sensor for $25 from your local electronics supply store.
If you do have 50 percent RH and your customers have lower values in the wintertime, an excellent finish that resists vapor movement will help minimize problems. Moisture change isn't good, but a rapid moisture change is worse than a slow change.
If you really do maintain 50 percent RH, you're fortunate not to have had a lot of trouble.
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