Wood Movement

CONTRACTION AND EXPANSION

Rustic Kithen Island-Bottom View-1In response to changes in the moisture in the air, wood expands and contracts across the grain but minimally along the grain. A tabletop, whether made of a single board or formed by gluing boards edge-to-edge, will have a range of movement of as much as 3/16 to 1/4 of an inch, depending upon the type of wood and the width of the tabletop.

Wood movement has both cosmetic and structural consequences. The cosmetic effect is that a tabletop, over the course of a year will change in size and sometimes in shape. In prolonged periods of low humidity, for example, a round tabletop will shrink across the grain and become elliptical. The change may go unnoticed in a large table, but in a small table it can be quite evident.

 

Breadboard-300x189A large rectangular tabletop, especially one with a substantial overhang, may cup or bow slightly, or get wavy along the end. The traditional preventive measure is the “breadboard end,” a strip joined across the end of the tabletop.

This helps to maintain flatness, but it has a cosmetic problem of its own: the joint between the edge of the breadboard end and the edge of the table will vary with wood movement. When humidity is highest, the tabletop will expand and extend beyond ends of the breadboard. When humidity is lowest, the tabletop will shrink and the ends of the breadboard will be proud.

If the tabletop is firmly fixed to the leg-and-apron assembly, two things can happen. The tabletop can buckle as it expands, or crack and split as it shrinks. It can also promote joint failure in the framework.

KEEPING THE TOP FLAT

Rustic Kithen Island-Bottom ViewMaking a tabletop flat in a way that doesn’t allow it to damage itself is imperative.

A common way to accomplish this with trestle and tavern tables is by screwing a batten or cleat to the underside. Mounting screws are run through slots in the cleat rather than through tight pilot holes to allow the wood to expand and contract. Ever useful, the batten might even double as a connection between the tabletop and the trestle or leg structure.

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Rustic pine live edge pine from threshing boards shaker stle legs Made By www.snoopersfurniture.ca