Electrodialysis stack and spacer for use therein

An improved electrodialysis stack and method of constructing the same wherein a multi-ply membrane spacer is used, the spacer consisting of a relatively thick and relatively flexbiel interior ply and two relatively thin exterior plies formed of a more rigid material than is the interior ply. These exterior plies are held together by a water-resistant pressure-sensitive adhesive. The resultant spacer may be adhesively bonded to cationic and anionic membranes on each side thereof, and thereby form a part of an essentially solid laminar dialysis stack which is free from cross-leaking and seepage problems.