Clamping cauls help you upholster seat cushions
Compressing upholstery foam while stapling fabric in place seems to call for at least four hands, and the result always seems to be a wrinkled mess. To make it easier, I notched the ends of a pair of 2x4s just longer than the length of my plywood seat panel to make clamping cauls. With the foam centered on the fabric and the panel centered on the upholstery foam, I used four clamps to compress the foam about 11⁄4 ".
To compress the foam evenly, measure at each end of the panel from the top of the seat panel to the workbench top until the distances match. Draw the fabric tight and staple the two sides running parallel to the cauls, as well as both ends at their centers. Release the cauls, then staple the fabric at each corner and trim the excess. When you release the compression, the foam will spring back and draw the fabric tight.
—Bob Wilson, Urbandale, Iowa