BCMG will inspect the render by tapping the area of render and will identify whether the render needs repairing.

If you tap an area of render and it feels 'live', it will probably sound hollow. 

This means the render is no longer bonded to the wall behind. If it has blown, it appears to bulge and should be broken away carefully to remove all loose render. Brush away any loose dust and widen the area around the edge with the point of a trowel or old screwdriver to improve the bond before applying new render.