Existing tiles are non-porous substrates
Product with Polymer composition should be used for tiling onto non-porous and glossy substrates. Efficiency ways for tiling onto these substrates are either;
1. Use ready-to-use paste adhesive, which is specially formulated for internal wall tiling onto existing tiles with no primer required.
2. Apply primer that composes of polymer to increase bonding property, and then tiling with high performance cementitious adhesive