On 21/04/2018 10:40, Dave Plowman (News) wrote:
Ordinary mortar isn't ideal for bedding ridge tiles as there will be
differential expansion between them and the main roof.

Marley concrete tiles are better set in a stronger mix. This is how
the 150 houses on my 1976 estate were built. Most of the houses
still have their original mortar at gable ends and along the ridge.

The sand seems to be a very fine red colour which they used to
make the initial mortar, then at the gable ends they scraped it back
about half and inch and over-mortared with some grey-dyed mortar before
the initial un-dyed mortar had set.

really tough, hard mortar too.