Hi, I have a basement room which runs below the steps to the main entrance (see pic). This has been there for years. Every couple of year we have been painting the steps with bituminous mastic as the waterproofing fails and water makes its way through. Has anyone got any tips or advice as to the best agent to use, perhaps one that you found lasts the longest? We have usually used Bostik Waterproofing bituminous mastic. Thanks