I need to patch a 6x6' area of a stone wall in the garden. On average, I'll be coming out by 2" to match the existing plaster but some areas, due to the way the rounded stones create deep crevaces, some areas maybe 4-5" deep. What's the best way to tackle this, scud the whole area and build up with layers of scratch coats until left with 10-15mm for top coat to finish? Or should I cement in smaller stones to build out the crevaces forst? What are the correct mixtures for each stage, or mainly the scud coat and if any additives go into this layer as know the others?
Thanks
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