Wood doc's Q&A

      Gene Wengert answers questions on inferior adhesives, end lift and estimated shrinkage. May 4, 2001

by Professor Gene Wengert

Had a terrible experience with a hide glue that has additives in it that allow it to remain liquid on the store/workshop shelf. Every time the temperature and humidity went up, the glue would 'let go' and chairs would deposit people onto the floor. Turns out the additive is iguanadyne and I am trying papaya juice to kill this enzyme. The question is (finally) are innocent iguanas harmed during this extraction to make this glue that, outside controlled environments, is virtually useless?

I have never heard of this. Also, are you sure that this is an enzyme? It is a new one for me. I suspect that the adhesive is inferior and "lets go" because the heat softens it, rather than any enzyme effect.


The enzyme isn't alive, so you cannot kill it. But you can deactivate it by heating (prior to use).

I am working for a flooring company in Johnson City, TN. We are having a problem with end lift in floating flooring product in the 8ft direction. Have you ever experienced any excess longitudinal shrinkange and swelling in maple? I am not saying this is the only cause. As a wood products grad I do not think this is applicable to the problem. I know some pine and tropical species have this problem. Do you have any insight?

I tend to agree with you that normally hard maple would not shrink enough lengthwise on one face and not the other to result in the end lifting. If it were moisture related, we would be seeing other problems too, such as a raised joint or open joints. You don't mention this, so I assume there is no other problem. We do have excessive longitudinal shrinkage as we get near the pith of the tree--is this a possibility? Is the product one solid piece? Is there a subfloor that could be moving? I would be glad to hear more, see pictures, sketches, etc. It is perplexing at this point, but certainly there is a good explanation.

I am going to slice 6/4 green northern red-oak (quercus rubra) to make flooring wear layers for a Swedish laminated flooring company to a thickness of .189" x 8-3/4" in width, and then dry these wear layers to 12-14% or so.

My question is, with a rather gentle forced-air kiln at a temperature of approx 95 degrees F, how much shrinkage should I allow for radially and tangentialy as well?

Also, as we are in Idaho, we use a lot of white spruce stickers. This should hopefully not stain the wood. Would spruce be the desired sticker-material?

The standard shrinkage values for northern red oak from green to 12% are averages (so half the pieces will shrink slightly more) and also vary for each species of red oak. To be 100% safe, I would expect 9% tangential and 4.5% radial. This means that all pieces will actually be too wide, so you may wish to save a little wood and make them 4% and 7.5% larger, which means that once in a while you will have a narrow piece, but not very often.

No problem with the spruce sticks if they are dry.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison

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