Gypsum board/Plaster board has a paper face.
Paper will lose strength when being in contact with water for a certain period of time. Considering factors for the adhesive used to fix tiles onto this specific substrate are;
1. Paste adhesive should be used, because of its ready-to-use property.
2. High performance adhesive with polymer composition, which is designed for tiling onto gypsum board, together with notched trowel should be used in order to control the amount of adhesive and also to prevent the water seeping into substrate layer.