Gluing Up Laminated Timbers Using Green Oak
Wood movement, clamping difficulties, and glue adhesion issues make this a problematic task. March 18, 2006
Question
I have a bandsaw and plan to cut red oak in 3/4 inch thick boards. I don't know if I will use 6 or 8 inch widths. I want to bend the boards into a 20 foot radius and clamp and glue them together to build arches for making buildings. I plan to use fresh cut green lumber and will use a nail gun to help hold everything together until the glue dries. I’m questioning if the glue joints will hold because of the moisture in the wood and the eventual shrinkage. Is there a glue that would work? I want to do it this way because I can easily bend the green wood and this way I do not need to sticker, dry and plane first. Any help would be appreciated.
Forum Responses
(Adhesives Forum)
From Gene Wengert, technical advisor, Sawing and Drying Forum:
The amount of shrinkage is so large, that even a lot of nails will not hold the wood laminates. There is no glue that will work on soaking wet oak. The problem is that the attachment sites for the glue basically are all occupied by water. Hence, you cannot chemically attach the glue. Further, many of the mechanical attachment sites are not available because the water is there. A few people have tried gluing wet wood by quickly drying the surfaces to be glued and then using a moisture friendly, fast-curing adhesive. In any case, warping is always excessive.
Another problem will be mating the surfaces to be glued. If you use a router to prepare the surfaces (you cannot just use the flat surfaces that you just bent as they will not be smooth at all), you will have to cut an inside and an outside arc. They are different shapes when using a router. Remember that for strong gluing, you need to have the mating surfaces within 0.006 inches with structural adhesives. In short, you cannot do this project green and it takes special care to even do it with dry wood.
From the original questioner:
I will retreat to dry wood and smooth surfaces, which means the wood will be too hard for the nail gun.
From Gene Wengert, technical advisor, Sawing and Drying Forum:
I would encourage you to use nails - just predrill the holes.
From contributor A:
You can steam bend the pieces. That process will change the memory of the grain so you don't have to rely on glue to hold it in place.
From contributor B:
These guys did it.....
"Six meter lengths were assembled in this way using a special finger jointing machine and special polyurethane glue working at a pressure of 40 atmospheres. The glue was selected as it will join wood with a high moisture content and resists the acidity found in green oak and cures rapidly. Furthermore the glue is pleasant to work with and is environmentally friendly."
Green Oak Timber Modern Architecture
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