Rising damp occurs when groundwater migrates up through the pores of a masonry wall by natural capillary action. The only way to stop rising damp where no dampproofing course has been installed is to install one. This can be done in two ways: by installing through-wall flashing or injecting water repellent. INSTALLING FLASHING Sometimes called physical dampproofing, the flashing physically blocks the upward migration of water. Because it requires cutting through the entire wall thickness, installing a mechanical damp course can take a long time and cost a lot. INJECTING WATER REPELLENT Usually a siliconate, silicone, or stearate is used as the dampproofing chemical. The liquid chemical migrates through the capillaries of the masonry material and after curing forms a water-repellent barrier that stops rising water. Laboratory testing helps determine the appropriate water repellent for a given substrate and the proper procedures for injecting it. Knowing the physical properties of the masonry, such as porosity, helps determine the amount of fluid needed, the drilling pattern, and the delivery rate. TEST BEFORE DECIDING Physical and chemical damp courses are effective methods of controlling rising damp. However, these treatments can be costly, time consuming, and are not easily reversible. Thus a thorough investigation of the masonry problem should be conducted before initiating work.