The lean screed is a layer that acts as an intermediary between the concrete slab and the tiling of the house or the exterior. If it is nicknamed the tiler’s screed, it is because it facilitates the laying of the coating by ensuring a very flat floor. In addition, it acts as a shock absorber to prevent cracks in the tiles and reinforce the thermal and sound insulation on the floor. Discover the characteristics and the composition of this thin screed as well as its essential role in the installation of the tiles.
What is a lean screed?
Lean screed is a layer of mortar that acts as an intermediary between the concrete slab and the flooring. It is thus placed so as to fill any defects in the supporting slab and to obtain a perfectly flat surface on which to lay its covering. It is therefore a solution perfectly suited to the laying of tiles and even acclaimed for an optimal result.
Thin, hence its name, the lean screed is only 4 to 10 cm thick. If it smooths the floor to facilitate the installation of your tiles, it also acts as a shock absorber to avoid the risk of the tiles cracking.
In general, the lean screed is placed on the concrete slab when it is perfectly dry, indoors and outdoors. It can therefore be placed in the house or for the realization of a terrace, the ground of a garden shed or an outdoor swimming pool deck. A separating layer can be added between the thin screed and the concrete slab to prevent them from adhering completely and to reinforce the sound and thermal insulation on the ground.
You can try your hand at laying your skinny screed, but we advise novice DIY enthusiasts or non-equipped hobbyists to seek the services of a professional. The installation of this coating is indeed more complex than it seems and the errors are frequent, and unfortunately difficult to recover. In addition, a thin screed is not very expensive to install, it takes 20 to 25 euros per square meter if you use a mason, a chapist or a tiler.
What is a lean screed made of and how do you make it?
The lean screed consists of mortar, which in turn consists of sand, water and cement or lime. On the other hand, it is under-dosed in cement or lime compared to the composition of the concrete slab since it contains only 150 kg of mortar per square meter against 350 kg for the concrete slab. It is this lower cement or lime content that gives it all its flexibility and reinforces its resistance. This is also the reason why it is ideal and recommended for laying tiles.
How to make a lean screed?
Equip yourself with cement, water and sand to make your lean screed that you will mix in a mason’s bucket. Also have within reach of the bastaings to delimit the surface of the lean screed, a spirit level to monitor its good flatness as well as a trowel and a float to distribute the product and smooth it.
Mix 25 kg of cement with 90 liters of sand. Mix well then add a little water until it forms a paste. The amount of water is determined depending on the area of the lean screed. Form a ball with the dough, it should be able to crumble.
Thoroughly clean the floor on which the lean screed is to be laid. Do not put it directly on a fresh concrete slab, wait at least one to two months for complete drying. Once the floor is clean, clearly delineate the surface of the lean screed using the bastaings.
Wet the slab and put a little cement on it with the float so that the lean screed adheres sufficiently. Pour the rest of your mixture and distribute it well over the entire surface. With your trowel, equalize and smooth the surface of the lean screed and remember to check the perfect horizontality of the whole using your spirit level. Fill in all the small holes visible in the area.
Be careful beforehand to think carefully about your organization! Indeed, once the lean screed is installed, you will not be able to walk on it. So avoid getting stuck in a corner of the room if you are operating indoors or against a wall if your construction is outdoors. Always make sure you finish by smoothing the area of your exit lane.
Finally, let it sit and dry for at least 5 days before getting down to laying your tiling.