Adding new concrete to an existing slab is possible if the old concrete is in good condition. Before pouring the new concrete, you must clean the surface and apply a suitable bonding agent. This will ensure that the fresh concrete adheres properly to the existing concrete. If there are spills on the floor, grinding or milling may be necessary to remove the upper few millimeters of the existing floor surface.
Unresolved issues with old concrete, such as cracks or frost, will carry over to new concrete if left unresolved. The new concrete should be approximately 2 inches thick and you should ensure that it is level and smooth before using the seals. If too much water is lost in old concrete, there will not be enough water to hydrate all the cement particles and the result will be a lower strength material. To patch the concrete, apply a thin layer of cement paint, pour a well-mixed concrete patch into the holes and clean the surface with a wooden float.
You may need help with laying the new concrete and stamping it. As seen above, concrete will not adhere to another concrete material if an effective concrete adhesive is not applied. In some cases, such as when installing a door or staircase, it may be necessary to get rid of old concrete and start from scratch.