premixed thinset mortar was generally not recommended for use in wet areas like showers. Traditional thinset mortar, which comes in dry powder form and needs to be mixed with water before application, is typically the preferred choice for tiling in wet environments.
The reason for this is that premixed thinset may not offer the same level of adhesion and durability as the dry powder thinset when exposed to constant moisture, heat, and potential movement in a shower environment. Wet areas, like showers, are prone to water exposure, and standard thinset mortar is designed to withstand these conditions, providing a stronger bond and better long-term performance.
However, there might have been advancements in premixed thinset products, so I recommend checking with the manufacturer or the product's label to see if it is explicitly rated for use in wet areas such as showers. If the premixed thinset is specially formulated and approved for shower use, it could be a suitable option. Always follow the manufacturer's guidelines and recommendations for the best results and to ensure the tile installation is successful and long-lasting.