By using Efflock, a secondary membrane to control efflorescence is not required. There are however, builders, architects and engineers who insist on including a secondary membrane as they like to 'cover all bases'. I can understand that; as builder myself, I like to include a few insurances in my work to avoid getting that phone call nobody wants. A secondary membrane remains good building practice, so long as excessive moisture is not sandwiched and trapped in between layers in the process.
I've also had situations myself in remedial work, where we opted to screed first, then apply a membrane and direct stick the tiles to the membrane. This approach also works well, and helps if there are finished height constraints with internal floor levels etc. Bonding the screed wet on wet directly to the concrete substrate means you can feather a tile bed out to 0mm to keep the finished floor level as low as possible, and this was an approach we took on a job back in 2010.
Above: Remedial work to a balcony. Waiting for tile screed to dry out sufficiently before a membrane could be applied.
The frustration of rain!!!
