Guide to building a timber frame home

Laminating an Arch Brace

Our original efforts to laminate a 9" deep arch brace from six 1-1/2" White Oak planks failed, as delaminating boards popped off like gunshots. We glued up that original lamination with Gorilla glue, which is activated by moisture. Unfortunately, we had over-steamed those boards to the point where they were probably fairly dry, not to mention inflexible, so it may not have been a fair test. We tried re-gluing that arch using West System epoxy, which also partially failed. On this attempt to laminate a 10" deep, 104" long arch with a 17" radius, we started with the West System, applying the mixture with a paddle.

Although our 1-1/8" stock was properly steamed and bent, trying to glue up all nine boards at once would have been near impossible. For one thing, all adhesives have a finite working time, and beyond that, it would be pretty tough to clamp all of the voids out of the whole stack at one shot. We decided to glue up the first four boards in one shot, attaching each successive board at one end with a single screw before coating its top surface with epoxy to receive the next board. Then we began clamping out the voids, beginning at the screwed end, using clamps made from Red Oak and rod stock. An electric power driver is used tighten up the clamps. Not shown here is how one of the clamps was clamped sideways on the arch to keep the pile in vertical alignment as we worked.

After drying for two days, we removed all of the clamps and the lamination held. However, the West System epoxy was not completely dry, possibly because the moisture content of the wood was around 18%. We switched to carpenter's glue for the next three boards (the yellow stuff). The dampness of the wood may be an inherent drawback in trying to build large laminations from steam-bent boards.
You can never have too many clamps when doing large laminations, and all of the extra clamps shown here were added after the custom Red Oak clamps were in place. We used wood clamping blocks with the metal clamps, in part to prevent denting the wood, and in part to avoiding the iron staining that quickly results from the contact of the metal with the acids in the green White Oak. When building up the arch, it's important to offset each successive board about a half inch in from the end, otherwise one end of the brace will end up with all the stepping and be a foot shorter at the top than at the bottom.

Throughout the milling and laminating process, we were careful to keep the boards in the order that they lay in the original timber. The resulting lamination and grain matching was a success. While the glue lines are just visible, they may disappear when the sealed White Oak darkens. The actual strength of the lamination is less critical in this application than in some other laminations, since the arch brace functions in compression. Of the three different adhesive systems we tried, Gorilla Glue, West System Epoxy, and yellow carpenter's glue, the yellow glue won hands down for strength, workability, and the best glue lines.

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