A Complete Guide to Tiling on Liquid Screed
For flawless tiling on anhydrite screed, there are three challenges you need to know about – moisture, laitance, and chemical reactions. The screed must be carefully tested to ensure it’s dry, the weak surface layer (laitance) must be removed, and a specific primer must be used. This priming step is vital to create a barrier, preventing a chemical reaction between the screed and the tile adhesive that can cause your tiles to lift. This guide will talk you through each of these steps.
We’re Capital Screeding, and we work with liquid screed every single day on sites throughout London and the South East. As a result, we know anhydrite screed inside-out, from how it dries to exactly how to prepare it for a perfect tiled finish. In this blog we’ll share our hands-on experience so you can get your project right first time.
What Is Anhydrite Screed and Why Does It Matter for Tiling?
Anhydrite screeds are different from cementitious ones because they use calcium sulphate as their binder. This is gypsum-based which makes it incompatible with the Portland cement that is found in tile adhesives.
Direct contact between the two, often with moisture in the mix too, triggers a chemical reaction known as ettringite formation. This process causes expansion at the bond line, leading to delamination and complete failure of the tiled surface. Which is why correct substrate priming is so important.
3-Step Guide to Preparing Anhydrite Screed for Tiling
That’s the science of anhydrite screed prep for tiling, now for the practical application. Follow these three key steps—in this exact order—to make sure that your anhydrite screed is perfectly prepared for a long-lasting tiled finish.
Step 1. Make Sure the Screed is Dry
Before you do anything else, you must be absolutely sure the screed is sufficiently dry for the flooring finish. Anhydrite screed takes around 49 days to dry fully. Ideally you should use a digital hygrometer to ensure the Relative Humidity (RH) is 75% or lower. Attempting to tile on a damp screed is one of the main causes of failure, so don’t skip or rush this step.
Step 2. Remove the Laitance
Next, you need to remove the weak surface layer, or laitance. The most effective way is to lightly abrade or sand the entire surface using a floor sander or scarifier. The aim is to remove the chalky top layer and expose the strong, stable screed beneath. Once finished, vacuum the floor thoroughly to remove all dust and debris.
Step 3. Apply an Acrylic Primer
This is the final, crucial step. You should apply an acrylic primer designed for calcium sulphate screeds. Apply the first coat and allow it to dry completely. This first coat soaks in and seals the surface. Then, apply a second coat to create a protective barrier between the screed and the tile adhesive, preventing any chemical reaction.
Bear in mind that every product is slightly different. Before you get started, take a moment to read through the instructions on the primer and adhesive you’ve chosen. Following the manufacturer’s advice is the best way to guarantee great results!
Get a Professional Finish with Capital Screeding
As you can see, preparing anhydrite screed for tiling is a precise science. Getting it right guarantees a floor that will last for decades, while getting it wrong can be an instant disaster. If you want to ensure a perfect, durable foundation for your tiles without the risk, our expert team of screeders is here to help. We provide professional screed installation and preparation across London, Essex, and the South East.
Contact Capital Screeding today for a no-obligation quote – 020 3369 3396
