Abstract: An improved spacer for use in an electrodialysis stack, the spacer comprising an inner ply, two intermediate plies, and two outer plies of a compressible material. These plies are held together by a water-resistant, pressure-sensitive adhesive with the inside of each intermediate ply being bonded to a side of the inner ply and each outer ply being bonded to the outside of an intermediate ply. The resulting spacer is assembled into an electrodialysis stack alternating with anion and cation selective membranes, the spacer and membranes being held in place by externally applied pressure to form a stack which is free from cross-leaking and seepage problems, and yet readily disassembled for servicing.