Abstract: An expansion joint control system wherein a blockout is formed between structural members such as a floor or wall and a gap allowing for expansion and contraction is defined between the structural members. The blockout defines opposed vertical faces and inwardly extending transverse surfaces with a flexible membrane spanning the distance between vertical faces. A slide plate is attached beneath the center of the membrane. Base members are positioned on the transverse surfaces for supporting the sides of the membrane and are in sliding contact with the slide plate. The slide plate and base members are formed of polymeric materials preferably having thermal expansion characteristics similar to concrete. The system elements occupy a blockout having a depth of one inch or less. The polymeric material can be readily bent on site making the system particularly useful for stadiums, etc. which have continuously changing elevations.