Is Sweetgum Too Unstable for Flooring?

      Sweetgum is highly prone to movement. However, sawn thin enough and heavily nailed (and glued), it just might work as strip flooring. February 19, 2008

I read a great discussion here recently about gluing down wide pine boards for flooring. The boards were sawn 1/2" thick, planed to 3/8", and then glued down. They looked great. That got me thinking. Could you do the same with sweetgum? I know it is used a lot in making veneers and looks nice when finished. I assume that the only reason it has not been used in floors has been the warping tendency. However, it seems that using the gluing technique on the wide pine flooring might work for sweetgum.

Forum Responses
(Architectural Woodworking Forum)
From Professor Gene Wengert, Sawing and Drying forum technical advisor:
I doubt that glue will hold down sweetgum if there is a large moisture change.

From contributor D:
I would T&G the sweetgum and then glue with a product like Bostik's Best or Rinaldi SLC 3000 and nail as well. Both of these adhesives are elastomeric and behave much like a rubber band. They allow for seasonal movement but always return the wood to the original position. Acclimation and moisture content at the time of installation is key. In Indiana we like 7-9% MV. The National Wood Flooring Association can advise you of the MV% for your area. Sweet gum should make a nice floor similar in hardness to yellow poplar.

From Professor Gene Wengert, Sawing and Drying forum technical advisor:
Sweetgum (redgum is the heartwood lumber name and sapgum is the sapwood name; black gum is tupelo) has a large tendency to warp (especially over small distances), so gluing will not work well when the MC changes. Sweetgum is not like other species that one might be familiar with in this respect. In fact, do not even expect that nailing will hold the floor flat when the MC changes. Note that mastic adhesives are very flexible and have very little strength, so they will not help hold the wood flat.

From the original questioner:
Thanks for the information. It's very helpful. Any opinions of how thin sweetgum would have to be in order for the glue to hold it down? I thought 3/8" might be thin enough for the glue to hold. Obviously, I couldn't go as thin as veneer, but maybe .25"? By the way, I'm going to try this experiment in a small storage room to start, so I'm not too worried about the results. However, I would like to get it right the first time if it's possible.

From Professor Gene Wengert, Sawing and Drying forum technical advisor:
If you take care to avoid moisture from the subfloor and if you use a non-elastomeric adhesive (that is, use a rigid adhesive), then I believe that 3/8" will work fairly well. Will you be putting the floor on sleepers or nailing to a wood subflooring? If nailing to 1/2" subfloor, the nails will not have high withdrawal strength... Try and hit a joist as often as possible and use lots of nails.

From the original questioner:
The subfloor is 3/4" plywood that is nailed and glued. It's encouraging to get some feedback that this may actually work. I haven't worked with gum but I like the challenge of trying new things.

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