cavity wall clearing

My father had rockwool blown into his bungalow's cavity wall around 10 years ago. There is evidence of condensation damp at floor level on the north and west facing external walls, and I suspect there was already air-blown sand within the cavities when the rockwool was added. I have read that...

Does anyone have any expericence of cavity wall clearing I have found the cavity walls have quite a bit of sand in them. The sand bridges the DPC and in some cases goes above 400mm above DPC. Aslo as you go down the wall it turns solid mortar. I was thinking of trying to get a rotary mutitool...