Control joints in veneer plaster over...

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Author Message Randall A Chapple, AIA, SE, CCS, LEED AP Senior Member Username: rachapple Post Number: 48 Registered: 12-2005 Posted on Wednesday, February 08, 2012 - 11:32 am:    Are control joints required for veneer plaster (ceiling) applied to a concrete substrate? Over gypsum board definitely but, can the veneer plaster move independently from the substrate which is monolithic? Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 454 Registered: 10-2007 Posted on Wednesday, February 08, 2012 - 12:17 pm:    If the concrete cracks the plaster should crack and if no cracks in the concrete there sould be no cracks in the plaster. Lynn Javoroski FCSI CCS LEEDŽ AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1390 Registered: 07-2002 Posted on Wednesday, February 08, 2012 - 12:32 pm:    We all know that concrete cracks. Veneer plaster control joints are recommended at 30' oc if there's no perimeter relief and 50' oc if there is. Is the space big enough for there to be control joints in the concrete? Is this gypsum plaster or concrete plaster? (Interior or exterior?) How is it applied to the concrete (metal lath (typically not used with veneer plaster)?) gypsum board base?) Gypsum veneer will crack if there's settlement. And assorted other questions... Randall A Chapple, AIA, SE, CCS, LEED AP Senior Member Username: rachapple Post Number: 49 Registered: 12-2005 Posted on Wednesday, February 08, 2012 - 04:20 pm:    The veneer plaster is gypsum applied to the ceiling of hotel rooms and in the corridors. The rooms are less than 30'x30' but the corridors will be longer than 50'. The veneer is applied directly to the concrete with no lath. Lynn Javoroski FCSI CCS LEEDŽ AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1391 Registered: 07-2002 Posted on Wednesday, February 08, 2012 - 04:38 pm:    According to National Gypsum (11th edition of their Construction Guide; page 50): treat monolithic concrete with a bonding agent; use a basecoat plaster followed by a finish plaster. Eventually, you'll have a 3/32" thickness minimum. There's no mention of control joints, but I'd honor the concrete control joints. It references ASTM C 843. There's more specific application procedures stated, too. Page 70 mentions control joints for exterior soffit board (30' apart and using "E-Z Strip", to coincide with expansion joints and places where wings should be separated (change of direction and intersections). You might want to call someone at National Gypsum - or another company - for additional information. Or the Gypsum Association? Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 455 Registered: 10-2007 Posted on Wednesday, February 08, 2012 - 06:45 pm:    If plaster is applied directly to the concrete the control joints in the plaster will not be effective. There are no crack control joints in concrete roof and floor slabs.