It is certainly easier if you use cornerstones with the sashing. If not using cornerstones I add the horizontal sashing to the blocks, sew the blocks together for each row, then add the vertical sashing to the bottom of each row & press well. Lay on table then place my ruler along the sashing seam line for row 1 & row 2 & pin where they should join. Continue in this manner until all is complete. Works well for me.