Slate Roof Problem

[dmsplat]

We have a slate roof, which has cement applied on the inside of the battens, presumably to form a seal between the slate and the batten for insulation (I have no idea if this is why it is there - a friend suggested it and it seemed a reasonable idea).

Anyhow, the cement seems to have aged to a point where it's all falling off, which is fairly messy!

The roof in general seems fine (one slipped slate after the Winter's snow).

My question is this: Should I replace the cement which has fallen? I am going to be getting a roofer in for the slipped tiles and will ask his opinion - but I would like to have some idea about the situation before I talk to anyone...

Thanks!

Dave

 

[Alastairreid]

The most common use of mortar under slates is called torching. This consists of a thin line of mortar trowelled across the top edge of each coarse of slate. The purpose of this mortar is intended to stop the very small amount of wind-driven rain or snow, common with slate roofs.

 

[henseyroofing82]

The most common use of mortar under slates is called torching. This consists of a thin line of mortar trowelled across the top edge of each coarse of slate. The purpose of this mortar is intended to stop the very small amount of wind-driven rain or snow, common with slate roofs.

Correct, before the common use of sarking felt all roofs had torching on tile/slate battens.
The torching was an unusual mixture of sand/sometimes coal dust, horse hair and lime.
Bizarrely I was once stopped from taking off a roof because of the possible risk of coming into contact with anthrax through the horse hair mix!