Mortar for Roof Tile Finishing

[marshian]

Extended the garage about 20 years ago (5.5m by 3.5m) matched the original pitched roof  (Marley Mendip concrete tiles and roofing caps) - been absolutely fine for years

 

No leaks into the garage loft space but I noticed the other day when cleaning out the gutters some of the mortar on the valley joints and the roofing caps has cracked - some has fallen out and dropped into the gutters  (see other post on gutter cleaning

 

Anyone know what mortar mix to use if I get up there and pull out the loose stuff and re-point/repair the areas where it's poor?

 

Soft sand or Sharp sand?

 

I'm quite happy working/walking on a roof - it's only single storey and I over speced the roof trusses because I use the loft garage for storage