The question of whether early workbenches were built from green wood or seasoned wood has a simple answer: yes.
But what was the common practice? For that question, I turned to A.J. Roubo’s “l’Art du menuisier” for the simple reason that Roubo’s work is still the legal standard in Europe for determining what is proper woodworking practice.
All the following translated passages will be found in “To Make as Perfectly as Possible: Roubo on Furniture” in 2016. The translations are by Donald C. Williams, Michele Pietryka-Pagán and Philippe Lafargue.
The logical place to start is the text for Plate 11. But Roubo doesn’t offer advice on the wetness or dryness of the wood. Following are the only discussions of workbench wood selection in Plate 11:
This bench is of elm or beech wood but more commonly the latter, which is very solid and of a tighter/denser grain than the other….
One should observe also to put the heart-wood side of the bench on top because it is harder than the other, and if the wood experiences dimensional changes, it is more likely to change from this side rather than shrinking from the other side.
It should be noted that throughout “l’Art du menuisier” Roubo discusses certain parts that must be well-seasoned (i.e. dry). But he doesn’t mention it in Plate 11.
If, however, we look to Plate 4 we get some clues. Plate 4 is about the maintenance of a wood yard outside your shop – how to stack green wood so it will dry without warping or rotting.
The reason you need a wood yard?
What I am saying here is only general. I know perfectly well that all woodworkers cannot have great wood yards nor large provisions of wood. But still, for reasons of economy, they should always do their best to be well prepared with samples, and to watch over their preservation as best as they can, so as not to be obliged to have to buy some from the merchants. The wood that they sell is almost never dry, and the woodworker will pay dearly for what the wood merchants have.
In the text for Plate 4, Roubo doesn’t discuss workbench wood directly. But workbenches are discussed:
Beech is found cut into planks of 15-18 lines, and even 2 thumbs thickness by 7, 9 and 12 feet in length.They also sell slabs of this wood for making woodworking benches, tables for the kitchen, and butcher tables, tables that have a length from 7-12, and even 15 feet, by 18-30 thumbs in width, and 5-6 thumbs thickness.
And Roubo also discusses dryness in general:
The more wood is hard, the more time it takes to dry. That is why one should not reasonably use wood that has not been cut at least 8 years in order to be able to do good work. It is not necessary, however, that it be too dry, especially for pieces of joinery, where the wood has no more sap and where the humidity is totally expunged: this cannot be appropriate [once the sap no longer is flowing from the lumber and the moisture has departed there is no need to season the lumber any further].
Interestingly, French timber merchants still follow this rule, according to Bo Childs, who brought over all the French oak for the French Oak Roubo Project. Our slabs were at least 10 years old.
What I take away from the text to these two plates is that seasoned wood was the norm in the shop. Roubo offered no exceptions for workbenches (something he does offer later in the book on garden woodwork).
This lines up with my experience building these benches: chances are the wood is going to be semi-dry. Not fresh cut. Not dry as a popcorn fart. Eight years is not enough time for these slabs to fully acclimate, but you can build benches with them. They’ll move around on you quite a bit the first year or so. But it’s easy to manage if you own a handplane.
— Christopher Schwarz