Rising Damp is caused by the same natural capillary action by which plants absorb moisture into their stems from the soil beneath. It becomes Rising Salt Damp when mineral salts are present in the soil and are drawn up with the moisture.
No system on the market can get rid of the salts and or any residual moisture already in the wall above where you have introduced the new Damp Proof Course. The residual moisture will dry out over a period of time depending on how damp the walls are and weather conditions. However the residual salts will continue to attract airborne moisture so it is imperative to introduce a salt retarder/moisture barrier into the new render if and when replastering.
Flaking paint, bubbling plaster, crumbling bricks, stonework and mortar are the indications of rising damp. As long as there is no soil or rubbish higher on the other side of the wall then it is rising damp. All of our applicators have moisture meters and are able to give you an accurate assessment.
If the existing render is bubbling then it is contaminated with salts and needs to be removed. Sanding back will not solve the problem and is a waste of time as the salts will reactivate and cause more bubbling.