Anhydrite Screed: Advantages, Applications, and Installation Guide

Anhydrite screed offers several advantages that make it a preferred choice for many construction and renovation projects. These include:

Anhydrite screed can be applied quickly, allowing for faster project completion compared to traditional screeds. It requires less time to dry and can be walked on sooner, reducing construction timelines.

Anhydrite screed naturally levels itself, resulting in a smooth and even surface. This property eliminates the need for extensive manual leveling, reducing labor costs and ensuring a high-quality finish.

Anhydrite screed has excellent thermal conductivity, making it an ideal choice for underfloor heating systems. It efficiently transfers heat, providing optimal comfort and energy efficiency.

Anhydrite screed exhibits minimal shrinkage and cracking compared to traditional cement-based screeds. This characteristic ensures long-term durability and reduces the need for repairs or maintenance.

Anhydrite screed is suitable for various applications in both commercial and residential settings. Some common applications include:

Anhydrite screed provides a smooth and level base for a wide range of floor coverings, such as carpets, laminate, vinyl, and tiles. Its versatility makes it suitable for bedrooms, living rooms, kitchens, and other areas of the home.

Anhydrite screed can withstand heavy loads, making it ideal for commercial and industrial environments. It is commonly used in offices, retail spaces, warehouses, and factories, providing a durable and long-lasting flooring solution.

Anhydrite screed is often used in renovation projects to level uneven or damaged substrates before installing new flooring. Its self-leveling properties help to overcome surface irregularities and provide a stable base for the desired floor finish.

Here is a step-by-step guide to installing anhydrite screed:

Ensure the substrate is clean, free from dust, and structurally sound. Repair any cracks or damaged areas. If necessary, apply a suitable primer to enhance adhesion.

Install edge insulation strips around the perimeter of the area to prevent screed from leaking out.

Follow the manufacturer’s instructions for mixing the anhydrite screed. Use clean water and a suitable mixing device to achieve a smooth and consistent mix.

Pour the mixed anhydrite screed onto the prepared substrate. Use a leveling device, such as a straightedge or laser level, to achieve the desired thickness and evenness. Allow the screed to self-level.

Once the screed has settled, smooth the surface using a trowel or power float. This process helps to achieve a seamless finish and further levels the screed.

Follow the manufacturer’s guidelines for drying and curing times. Anhydrite screed typically requires less drying time compared to cement-based screeds. Avoid foot traffic and heavy loads until the screed is fully cured.

After the screed has dried and cured, you can proceed with the installation of the chosen floor covering according to the manufacturer’s recommendations.

Anhydrite screeds have become quite common as they offer benefits over sand and cement screeds. However, tilers must be aware of a number of potential anhydrite screed problems.

When a cement-based adhesive is applied directly onto the floor, cement in the tile adhesive reacts with the gypsum in the screed resulting in a mineral called ettringite being formed at the interface. The associated structural change is sufficient to cause a complete debond of the cementitious adhesive away from the screed base.

As anhydrite cures, a weak layer of laitance is formed on the surface. This layer is too weak to tile onto and also slows the drying time of the screed.

Firstly, what is anhydrite screed? Anhydrite screeds are made from inert fillers such as sand, with a binder system based on calcium sulphate. Consequently they can look very similar to a sand/cement screed. Anhydrite will tend to appear lighter, sometimes almost white, but in practice it is difficult to identify an existing anhydrite screed from a traditional one.

If a screed is known to be anhydrite it must be thoroughly sealed before the application of a cement-based tile adhesive. If the screed type is not known and it is believed that it could be anhydrite, the screed should be thoroughly sealed as a precaution.

1. The cured screed will have a layer of anhydrite screed laitance that will need to be removed after 2-6 days (dependent on brand of screed used). This will provide a dense surface to tile onto and will aid drying.
2. Ensure the floor is fully dry – the residual moisture level should be less than 0.5%. Drying times vary according to the brand of screed used. Some are designed for fast-track use, whilst others require the standard drying times. If no other information is available assume the screed will take 1 day per mm up to 40mm in thickness to dry in normal conditions. Screeds thicker than 40mm will require 2 days per mm.
3. Seal the floor with weber PR360 — which can be used as an anhydrite floor primer — repeatedly until no more is absorbed and allow the primer to dry before tiling. An uncoupling membrane can be used to reduce stress on the tiling layer and to ensure that ettringite does not cause a failure.

Fix tiles into a solid bed of weberset pro lite – rapid or weberset rapid SPF at least 3 mm deep. Leave joints at least 3 mm wide for grouting and make provisions for movement.

Fill the joints between tiles with weberjoint premium, and use weber joint silicone sealant to fill perimeter movement joints.

Anhydrite screed offers numerous advantages and applications, making it a popular choice for flooring projects. Its self-leveling properties, rapid installation, and thermal conductivity contribute to its appeal. Whether it’s for domestic, commercial, or renovation purposes, anhydrite screed provides a smooth, durable, and high-quality surface. By following the installation guide and utilizing the expertise of professionals, you can achieve an excellent finish that meets your specific flooring requirements.