Can a new screed be laid over an existing screed?
Yes if the old screed is sound and well bonded, and if the available height allows at least 4 cm. Below that, a levelling compound or removal is needed.
Yes if the old screed is sound and well bonded, and if the available height allows at least 4 cm. Below that, a levelling compound or removal is needed.
Covering rather than demolishing saves time and money, and avoids the need to remove rubble. However, the old screed must be suitable, and the decision comes down to just two criteria: its condition and the remaining height.
First and foremost, you must ensure that the substrate is firmly bonded to the slab and is not crumbling. Three checks are sufficient:
This is often the deciding factor. A new floating screed requires at least 4 cm, or more if insulation is added. You must add the thickness of the final floor covering and then check the consequences: clearance under doors, the height of the first stair step, thresholds, and transitions to adjacent rooms.
When only a few millimeters remain, a screed is no longer the right solution. A self-leveling compound or a thin-layer leveling compound is enough to correct flatness; the difference between the two techniques is explained in our article leveling compound or screed.
If covering is approved, the old surface must be cleared of all glue, paint, laitance, or flooring residue, then thoroughly vacuumed. A simple sweep is not enough: vacuuming is essential for proper adhesion. If low spots remain, planing or localized repair it happens before, not after.
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