Crumbling sandstone building

[scrumlish999]

The stonework on the front of my is around 120-year-old building and is degrading. I have been doing some research into this over the last month and a building of this age was originally built using lime mortar in between the sandstone blocks. Over time the mortar requires to be repointed. If the wrong mortar is used. I.e., cement rather than lime mortar, this can cause problems for the stonework. Lime mortar drains properly and allows the stonework to breath. Cement stays wet for longer thus keeping the sandstone wet and it starts to crumble.

 

Here is a YouTube video to explain.

 

https://youtu.be/3Omxc4OK9eE?si=rZ86qRxLLT27zd8s

 

I have spoken to the local council planning, building standards guy. He said that the stone used to build the buildings in Dundee was generally poor quality all those years ago. It leads to spalling which is the effect we are seeing on the stone. Our building is super exposed to the elements and means that our stone is likely to degrade more quickly. 

 

I've attached some photos of the stonework at the front outside my flat, ground level. You will see from the photo that the flat above stonework is degrading above my bay window. The front of the building is degrading in many places.

 

How should we fix this? Will simply removing he old perhaps cement cased pointing and replace with a lime mortar sort things out or as the stone has begun to crumble, will it still be porous to heavy rain?

 

Should the worst parts be brushed down and then coated with a lime mortar mix?

 

Any help would be much appreciated.

 

Cheers

 

[kandgmitchell]

It is interesting that the crumbling section lies between two dressed details - the stone cill above and the string course below. The cill also has a crack in it above the worst weathering. There doesn't seem to be much overhang on the cill and the string course seems to have a flat top edge. These may conspire to keep the stone panel between the two wetter than the rest of the wall. The crack in the cill will also feed water into the top edge of the stone and then freeze thaw action gets to work. Be interesting to know if other matching properties in the street suffer the same issue.

 

Curing the problem would certainly start with filling that crack in the cill. Beyond that you can't really change the cill and string course. It may be a job for a mason to cut out the face of the worst block and insert a shallow facing stone. Might be worth having one look at it. 

 

Lime is more porous but then it allows the water to evaporate again. Think of lime as an overcoat that gets wet then dries off whilst cement is like a plastic mac. It holds back the rain but once water gets inside it it can't get out.

[scrumlish999]

Kandgmitchell

Firstly thanks very much for taking the time to give me such a detailed reply. This is my first ever post. So cheers.

I will contact a stone mason and show them your comments. Nice one