Painted wall-hung slates

[RJBB]

Building built approx 1905, Lyme Regis. The roof above my balcony was not sealed properly. Ever since then I have had mould type marks on the wall hung slates.
It looks as if water has come through into them. The roofer/builder is not much use. He maintains that the slates are rotting.
Do slates rot???
And, how do I fix this, remove all previous paint and re-paint?? or just paint over it.

 

[mardinor]

Well, seeing as slates are famously used for roofs to keep water out and damp-proof courses to keep water from rising then I hope not!

In your photo it is possible that water has entered between the slates and the paint film from the joint above (but would expect that to cause bubbling not 'mould'). If it is indeed surface mould that you can remove with bleach and scrubbing, it must be on the surface caused by cold slate and poor ventilation. But what has changed? Perhaps the leak above has increased the moisture in the area.

What to do? I'd scrub with dilute bleach or mould killer, leave it a year to make sure the leak is fixed, then repaint with a key to the paint. Nothing more drastic than that.

 

[RJBB]

Well, seeing as slates are famously used for roofs to keep water out and damp-proof courses to keep water from rising then I hope not!

In your photo it is possible that water has entered between the slates and the paint film from the joint above (but would expect that to cause bubbling not 'mould'). If it is indeed surface mould that you can remove with bleach and scrubbing, it must be on the surface caused by cold slate and poor ventilation. But what has changed? Perhaps the leak above has increased the moisture in the area.

What to do? I'd scrub with dilute bleach or mould killer, leave it a year to make sure the leak is fixed, then repaint with a key to the paint. Nothing more drastic than that.

Thank you. That makes a lot of sense. RJBB

 

[RJBB]

Thank you, that makes a lot of sense. RJBB