Repointing roof valley

[Al@n]

Need to repoint roof valley as the mortar has come away/crumbling

What ratio mix should I go with?

Looking online people have suggested 3:1 or 4:1 with a 50/50 mix of building sand and sharp sand.

Should I add any additives to the mix?

 

[Al@n]

Bump

 

[23vc]

Mix is about right but you probably want to get the tiles bedded down onto it rather than just push it in

 

[^woody^]

Yes, 3:1, based on sharp sand with building sand added only to help workability (no less than 1/3 sharp sand), no additives and the tiles should be re-bedded not repointed.