Liquid screed floors, such as anhydrite screeds, have become very common as people recognise their various benefits. It is a relatively easy to lay, low cost, fast-drying, self-levelling floor option that works especially well with tile floors.
At UK screed, we see many homeowners take advantage of tiled floors laid on liquid screed substrate, as part of efficient underfloor heating systems that radiate heat nicely throughout the home.
However, tilers must follow the right procedure for optimal effect and to avoid chipping and cracking in the future. We explore some advice and best practices for tiling on liquid screed floors.
Gypsum Content and Debonding
The ingredients in liquid screed floors can lead to debonding if the tiling is not handled correctly. For instance, anhydrite screed contains anhydrous Calcium Sulfate and aggregates. When water is added, the binders will form calcium Sulfate dihydrate – also known as Gypsum.
When floor adhesives are applied directly onto the floor, cement in the substance reacts with the gypsum in the screed creating a mineral called ettringite on the surface of the floor.
This structural change can cause a debonding process where the adhesive is no longer effective at bonding tile flooring to the liquid screed floor base.
Before applying adhesive to the screed and laying down any tiles, it is crucial to ensure that the moisture content is low enough for the required floor finish. This can be achieved by waiting long enough for the floor to dry naturally, around one week after being laid.
You can also use drying techniques and equipment to speed up the process and start tiling sooner. Air temperature and the total volume of the screed floor will affect the speed at which moisture evaporates away.
Sanding the Surface
Before laying tiles onto liquid screed, it is important to remove any substances from the top layer that may have accumulated during the process. This could be any solid materials or objects that have found their way into the mixture or become dislodged from below, eventually floating to the surface as the mixture dries.
Also, in the case of laitance, a certain quantity of cement also comes to the surface, forming a thin layer of cement paste at the surface. This is known as laitance and must first be removed before any tiling can occur.
As laitance is a weak layer of fine particles deposited on the surface of the screed, it’s not that hard to remove. However, if you fail to do so, you could have an uneven surface unfit for tiling.
Laitance should be removed with light abrasion using a suitable sanding machine. Finally, remove all excess dust completely with a vacuum cleaner. This is best done 4-6 days after the application of the screed.
The Process
- Assess and Prepare the Floor
Ensure the floor is fully dry, even and smooth, with any laitance sanded away. You must leave your floor to dry so that the moisture content does not interfere with the structure or integrity of the floor in the future.
Some mixtures are designed to dry especially fast, so check with us first about how long it will take for you to move to the next stage of your project.
- Seal the Surface
Anhydrite screed floors must be thoroughly sealed before the application of a cement-based tile adhesive.
- Use the Right Adhesive
Next, use the right adhesive for the kind of screed you’re using and the type of tiles you are fixing to the surface.
- Lay Tiles
Fix tiles carefully and evenly with enough space left between each one so that you can apply grout and silicone suitably. Something like 3mm is recommended.
- Apply Grout
Fill the joints between tiles with suitable grout and any final sealant mixture to complete the floor surface and achieve uncompromised integrity across the whole surface.
Looking for a Liquid Screed Company in Gloucestershire
UK Screed Ltd is a Liquid Screed Company in Gloucestershire that can provide advise on floor preparation and planning approach for your home renovation project. Our self-levelling screeds may be just what you need to ensure your tile application is as flawless as you’d hoped, with 100% adhesion and smoothness across the entire surface.
