Clamping Pressure For Wood Glue

As the glued up piece goes through the normal expansion and contraction cycles in response to temperature and humidity changes the elevated forces you squeezed into the wood with excessive clamping pressure keeps trying to return the wood to its original shape.

Clamping pressure for wood glue.

Proper clamp pressure will also compensate for any imperfections between the two mating surfaces. In addition to getting the two pieces of wood close enough together for proper gluing pressure also squeezes out the excess adhesive and pushes the glue into the microscopic nooks and crannies. Second as the glue releases moisture causing the wood to swell clamping overcomes this pressure and prevents the joint from opening up. Third it overcomes minor surface imperfections between mating surfaces.

Too little pressure will fail to achieve any of these benefits. In some cases where adhesive is only on one of the mating surfaces pressure also assists in transfer of the adhesive to the other face. When those forces cause a failure it might not involve the original glue joint. Additionally consider how much the moisture in the wood will cause the wood of the joint to swell.

Dale zimmerman of franklin international maker of titebond woodworking glues recommends 100 to 150 pounds per square inch psi for clamping softwoods and 175 250 psi for hardwoods. And fourth clamping holds parts in position until the glue cures. When we tested one handed bar clamps issue 139 we found that they provided pressure just into the softwood range or a bit less. Too much glue can cause glue run out problems that will likely cause other issues at the time of finishing the project.