Lead is traditionally used for the flashings around windows and chimneys and to line valleys in the roof – its primary purpose is to make these areas and joints waterproof.
Mortar is not used all over the roof, but it is traditionally used on ridges, hips and verges, where the tiles are bedded into a thick mortar layer. Mortar is actually the main cause of problems in modern roofs. Mixing and applying mortar properly is a skilled and time-consuming task: any shortcuts lead to the mortar cracking and water leaking.
Neither of these materials are required on modern roofs – all can be replaced with dry fix components (see our section on Why Dry Fix). Dry Fix can be more expensive than lead and mortar but more reliable.
