Many contractors use the Sovereign Hey’di K11 Grey System for all underground damp proofing works. This product can stand up to 120 feet of head water pressure and is ideal for converting cellars into living accommodation. This application is also used where the external ground levels are higher than internal floor level or that the property is sculpted into a hillside. It is also extremely effective when applied to solid natural stone walls as they are susceptible to rising and penetrating dampness. In these circumstances a double strength external water repellent is applied to the outside of the property. Tanking works carried out in an underground application usually carry a ten year guarantee whilst those above ground carry a thirty year guarantee.