Hi, I have built a 700 high retaining wall using hollow blocks filled with concrete. I backfilled with mud not realising I needed a membrane, I have dug out the back and lined with a plastic membrane the best I can. My question is, I intend to cover the wall with porcelain paving slabs, shall I paint a membrane to the outside (if so what would you recommend) and would the paving primer slurry take to this ok? Or can anyone offer another solution. Thanks in advance.