General roof maintenance. When this house was built the tiles were given a very short head lap. At the ridge line the gap between the two top course of tiles is too wide. The roof should have had at least two more course of tiles on each side. The mortar was a very weak mix with not much cement in it which has caused it to fail prematurely. We have made our usual mortar which is a mix of 3 parts sand to 1 part cement. Then plenty of bedding mortar has been laid to ensure that the ridge tiles adhere properly.