As I write today's blog, the weather in Sydney has warmed up. It's a sunny 22 degrees, which is not too hot yet, but with the combination of wind, it can spell disaster for a screed.
The repellent effect of Efflock means that if a screed loses its gauging water/ construction moisture in evaporative conditions, it cannot be 'watered back in'. With Efflock, or with any water repellent additives, it is imperative that the moisture is protected from being lost at all during the process, and in the hours and days after it is laid. For example, to counter evaporation, it's worth mixing the screed with as much water as practicable, protecting the area with shade, and then moisture curing with something like damp hessian. (It's important to note that the silicon content of Efflock can make a screed mix appear and feel wetter than it actually is).
AS 3958:2023 Installation of Ceramic and Stone Tiles has information on screeds under Appendix A. Notably, under A.8 it says: "Sand/cement and fine concrete screeds should be cured for at least 7 days and be subjected to continuous air drying after curing for at least 2 weeks before the bed and tiling are applied."
There may be exception to this depending on the circumstances. For example we can postulate effective curing would be provided by laying tiles early over a green screed. (Only strong tiles such as porcelain tiles or strong stone should be considered for laying over a young screed, as weaker 'twice fired' tiles might not withstand potential forces from a green screed cracking, curling or shrinkage). A.8 goes on to say: "Some cementitious adhesives are suitable for use on screeds that were laid as little as 12 h previously. However, many waterproofing membranes require low residual moisture content in the screed prior to their application. Refer to the manufacturers' instructions."
If you're seeking advice on your next tiling project, feel free to give Ben a call on 0414 730 736.
AS 3958:2023 can be purchased digitally or in hard copy here.