Laying paving slabs over an existing concrete base involves applying a mortar layer and setting the slabs onto it.
Slab over concrete, typically referring to laying paving slabs onto an existing concrete base, is a process that provides a new surface layer, ideal for patios, walkways, or outdoor areas. This method uses the existing concrete as a stable sub-base.
Preparing the Concrete Base
Before laying any slabs, the concrete base needs to be prepared. This involves cleaning the surface thoroughly, ensuring it is free of debris, dirt, oil, or any loose material. Any significant cracks or unevenness in the concrete should ideally be repaired to provide a sound foundation.
The Laying Process
Once the concrete base is clean and prepared, the process of laying the slabs involves applying a bonding layer and then setting the slabs. Based on standard practice and the provided reference, the key steps for laying the slabs on the mortar bed are:
- Applying the Mortar: Using a trowel, spread a layer of mortar onto the preformed concrete base. This mortar acts as the bedding layer for the slabs. The layer should be at least 25mm thick. Ensure the mortar is evenly spread to create a consistent bed for the slab.
- Laying the Paving Slabs: Carefully lay the paving slabs onto the mortar bed. Position each slab correctly according to your planned pattern. Pressing down firmly to ensure a good bond. You may use a rubber mallet to gently tap the slab into place, ensuring it is level and properly seated in the mortar.
Practical Considerations
- Mortar Mix: The type of mortar used is crucial. A typical mix for this purpose is a strong sand and cement mix, often with a plasticiser added for workability. Some people may use a specific bedding mortar product.
- Bonding Slurry: To enhance the bond between the concrete base and the mortar layer, and between the mortar and the slab, some professionals recommend applying a bonding slurry to the concrete base just before applying the mortar and to the back of each slab just before laying it.
- Jointing: Once the slabs are laid and the mortar has set sufficiently, the gaps between the slabs (joints) need to be filled. This can be done using pointing mortar or a jointing compound designed for paving.
- Working Area: Work in manageable sections, spreading only enough mortar for a few slabs at a time, as mortar can dry quickly, especially in warm weather.
- Slope: Ensure there is a slight slope (fall) away from buildings or structures to allow for proper water drainage.
By following these steps, especially correctly applying the mortar and carefully laying and bonding the slabs as described, you can successfully lay paving slabs over an existing concrete surface.
