Cag

First you've got to understand the cause, in order to know what to do: It could be insufficient cleaning: If the existing mortar was not adequately cleaned and prepared before applying the new pointing, the adhesion could be compromised. OR it could be incorrect mortar consistency: If it's too dry, it may not adhere properly. OR it could be temperature fluctuations: Rapid temperature changes, especially during the curing process, can affect the mortar's adhesion. A few ideas I'd suggest: Consider using a 3:1 sand-to-cement ratio as suggested. This can provide better strength and adhesion. Add SBR: Styrene Butadiene Rubber can enhance the flexibility and durability of the mortar, especially in outdoor applications. Remove any loose mortar, dust, or debris from the joints. Use a wire brush or a chisel to clean them thoroughly. Before applying the new mortar, slightly dampen the surface of the existing slabs. This will help the mortar adhere better. Ensure that the joints are filled to the top with mortar. Avoid leaving voids or gaps. Use a pointing tool to compact the mortar firmly into the joints. Finish by smoothing the surface of the mortar to a consistent appearance. During the curing process, protect the repointed areas from excessive moisture loss. This can be done by covering them with a damp cloth or plastic sheeting. Avoid direct sunlight - it can cause the mortar to dry too quickly, affecting its strength. If the gaps between the slabs are particularly wide, a joint filler can be used as a base before applying the mortar. Just for extra credibility - I'm a professional landscaper from https://battersealandscapers.co.uk/ - hope this helps