In the field of construction and renovation, the installation of tiles often requires the creation of a lean screed. This thin layer serves to protect the tiles while ensuring their stability. It is essential to respect certain proportions to achieve a quality lean screed. Here, we unveil everything you need to know about the dosing of a lean screed, based on sand, water, and cement.

The composition of the lean screed

A lean screed mainly consists of three elements: sand, cement, and water. They must be mixed in precise proportions to obtain a homogeneous solution suitable for the type of surface to be tiled.

It is important to note that the dosage of these three components will also depend on the size of the area where the screed is to be applied.

The basic mix

To prepare a lean screed, here are the ideal proportions:

• 25 kg of cement
• 90 liters of sand

These quantities are essential to obtain a relatively thick mixture that will facilitate the laying of the tiles.

The addition of water

Once the basic mixture is homogeneous, water should be added. The volume of water added will depend on the type of surface to be covered, but also on the desired consistency for the screed.

The steps for preparation and installation

To successfully create a lean screed, here are the different steps to follow:

1. In a wheelbarrow or a large container, mix the cement and sand until you obtain a homogeneous powder.
2. Gradually add the water while continuing to mix until the consistency of the screed is pasty and easy to work with.
3. Spread the screed over the surface to be tiled, ensuring it is evenly distributed using a trowel.
4. Check with a spirit level that the screed is flat and make any necessary adjustments before laying the tiles.

Some additional tips and tricks

Here are some recommendations to optimize the success of your lean screed:

The choice of sand

Opt for medium grain masonry sand (0.2 to 1 mm), which will provide better adhesion to the screed.

The moisture of the mixture

A too high addition of water to the mixture can promote the formation of cracks during the drying of the screed. Therefore, it is essential to add water gradually until the ideal consistency is achieved.

The drying time

Allow the lean screed to dry for at least 24 hours before laying the tiles. This duration can vary depending on the thickness of the layer and the climatic conditions, such as ambient humidity.

Dosing a lean screed based on volume

To calculate the volume of screed needed for a construction or renovation project, simply use this formula: length x width x thickness (in meters) to obtain a result in cubic meters (m3).

For example, to create a lean screed of 1 m3 over a surface of 20 m2, you will need:

• 1500 liters of sand
• 250 kg of cement
• 125 liters of water

Mastering the dosing of a lean screed will guarantee its quality and effectiveness in protecting and laying your tiles. Feel free to slightly adjust the proportions based on the specifics of your project.