Leaking bay window with sandstone roof

[mistertaylor]

We have a Victorian terrace with a bay window roof made from sandstone blocks that leaks under heavy or prolonged rain. There’s been a previous repair to the joints between the roof “tiles” (with some sort of sealant) which has now degraded, especially on the front most row, causing water to drip down the window frame at the corresponding points inside. I believe it only leaks when the stone has become saturated under heavy or prolonged rainfall and it therefore seeps through.

The there’s no lead flashing as the blocks are cut to sit flush with the brickwork where the bay joins the wall.

Can I scrape out the old sealant and replace with something suitable (recommendations please) and then seal the whole bay window roof with some Thompson’s Waterseal (or similar)? Would this cause any unforeseen issues? Thanks!

 

[^woody^]

Choose a polymer mastic, maybe clear.

For the stone, use a silane/siloxane product which perform better and have much longer life than Thompsons or similar silicone based sealers.

Check the actual product is suitable for that stone. Some are not.

Check the manufacturer's instructions, but you will likely need to clean all moss and algae from the surface and treat it with a biocide for the sealer to work.

 

[datarebal]

Rake it out , especially the lintel joints and point in lime mortar , properly packed and knocked back it'll be fine