When and why do I need dentil slips on my roof?

Dentil slips are inserted into the mortar along mortar bedded ridges and hips to help prevent the mortar slumping and cracking. Dentil slips are only required for profiled tiles (which have a curved cross section) where the profile depth of the tile is 25 mm or more.

Very often the dentil slips in a bedded ridge are left partially exposed as a traditional aesthetic feature. It is less common to expose the dentil slips in the mortar bed at hips because of the irregular nature of the cut tiles.