b'3. MUSHROOM GROWING OUT OF A WINDOW WEEP.4. STUCCO CRACKING AT BACKER PANEL JOINTS. 3 wasnt easyreplacement with a more climate-appropriate design CANADIAN CANCE I R SOCIETYwas recommended. CANCER PREVENT ON & SURVIVORSHIP CENTRE ADVENTURES IN VANCOUVER, BCBUILDING SCIENCE #4A commercial retailer wanted us to determine the cause of long cracks in the stucco finish on their new claddingWe deliver(photo 4). While there may be lots of other reasons for stucco cracking, inuncompromisingthis case a close-up review of explor-atory openings showed that the cracksperformance.occurred predominantly over joints in the backer board. We also observed that the backer board had not been taped together, contrary to the suppliersWe are Entuitive.recommendation. We concluded that when the scratch coat of the stucco was applied, there could be differential movement of the adjacent panels of backer board. Then, when the cementi-tious material finally set up, there couldbe a step in the back of the stucco, with different thicknesses based on the relative displacement of the backer board. This step would create a stress concentration, and when the stucco experiences thermal expansion and contraction (the effect was more pronounced on south-facing expo-sures), the stress concentration wouldSUSTAINABLE BUILDING CONSULTINGpromote crack propagation from theADVANCED PERFORMANCE ANALYSISinboard surface, which would eventuallyBUILDING ENVELOPE BUILDING RESTORATIONtelegraph to the exterior. BRIDGE ENGINEERINGCONSTRUCTION ENGINEERING A simple, cost-effective solution in thisFIRE ENGINEERINGcase was to recommend installing controlPEDESTRIAN MODELLINGSPECIAL PROJECTSjoints where the stucco had indicatedSTRUCTURAL ENGINEERING that such joints were preferred, but theTRANSPORTATION STRUCTURESpreventive solution for future construc- WOOD DESIGN SERVICES tion would be to tape the backer boardentuitive.comtogether so that adjacent panels move in unison, thus preventing the step. This isVANCOUVER| CALGARY |EDMONTON | TORONTO | OTTAWA | NEW YORKnow generally recommended by suppliers of the backer board, but at the time it was a novel idea.FALL/WINTER 2023 17'