Need advice on fixing crumbly exposed footings previously dressed with render – what’s the best fix for a 2030mm gap?

Got some crumbly footings, huh? Sounds like they could use a little fixing up. For a gap that’s between 20-30mm, you might want to consider using a cement render. A mix of sand and cement in a ratio of 3:1 or 4:1 should do the trick, depending on the condition of the existing material.
Before applying the new render, be sure to remove any loose material and slightly dampen the area; this will help the new render stick better. Press the sand and cement mix firmly into the gap.
If you’re concerned about future crumbling, adding a waterproofer or plasticizer to the mix could help. This will make the render more adhesive and resistant to water. Once it’s dry, finish it off with a high-quality exterior paint or sealant to protect it from the weather.
For larger areas or persistent issues with crumbling, it might be best to seek advice from a professional for a more thorough solution.
Hope that helps with your footing problem!
Cheers,
Robert