Composting can be used to convert organic wastes into valuable soil amendment products. Other waste products that contain required soil nutrients can be added to the compost to further enhance the resulting product. Waste gypsum wallboard (WGW) is commonly landfilled but has the potential to supply sulphur to the soil. Diversion as an additive to municipal composts is an alternative pathway for utilization of WGW. This study focused on characterizing the raw WGW from Construction and Demolition sites for total metal content of the WGW.  A study was conducted  using a continuous mix stainless-steel in-vessel composter to compare total and bio-available (DTPA extraction) metal concentrations in composts with and without WGW. The metal concentrations in the treatments were evaluated against the Canadian Council of Ministers of the Environment Compost Quality Guidelines.