Repointing stonework

[andy63]

Hi, I'm new to this forum and am hoping I can get some advice in making some repairs to a house I've bought. It's a stone built house that's around 120 years old. There are issues of damp in one wall in particular. The wall had been rendered and plastered over using modern products. I decided to remove the plaster and render, exposing the stone wall. The wall has dried out considerably. My question is for the next steps. I am thinking of leaving the stonework exposed and just repointing. I'm not clear on what mortar to use. I believe that modern cement is not the thing to use. I'm a bit confused regarding hydrated and hydraulic lime. Some say to add cement as part of the mix which I thought you shouldn't use in an old house like mine. I'd also like the mortar to be darker to look like what's already there. Is there an additive that can be used to vary the colour of the finished repointing? I also have some timber in the stone wall that has gotten wet and is breaking down. Can it be removed and stone put its place? There's a section of wall that is brick, around the opening for the fire. I'd like to replace it with stone but I'm not sure if that can be done. The bricks have been badly constructed and protrude out of the surrounding stonework by quite a bit. I would appreciate some guidance, please. Thank you!

 

[alexander]

hydraulic lime is the better option , some of the bigger gaps you can fill in by bedding some new stone work, hydrated lime will not set without an additive I.E, cement to help it & should be avoided, you can by lime mortar that will dry a darker colour you can also buy additives to change the colour but you need to experiment a bit with the dyes to get to the colour you require

 

[andy63]

hydraulic lime is the better option , some of the bigger gaps you can fill in by bedding some new stone work, hydrated lime will not set without an additive I.E, cement to help it & should be avoided, you can by lime mortar that will dry a darker colour you can also buy additives to change the colour but you need to experiment a bit with the dyes to get to the colour you require

Hi Alexander. Thank you for your help!

 

[stuart45]

If you are going to use a hydraulic lime an NHL2 would probably be the best as it's an internal wall. With bigger joints pick a coarse sand with a larger grain size. Small joints need a smaller grain size. A rule of thumb is that the larger grains in the sand are no bigger than 1/3rd of the joint size.
You can replace the timber and bricks in the wall, but care is needed, especially in random rubble stonework, as it's normally less stable than brickwork.
When using a mortar dye, remember that it lightens over time.

 

[Itchinfilth]

That looks by the colour that ash may have been added to the mix. I'm no expert on the properties this bring and suitability but my external walls were pointed in this way assume in the victorian period and it held up ok despite it being covered in cement for 40 plus years.

 

[andy63]

If you are going to use a hydraulic lime an NHL2 would probably be the best as it's an internal wall. With bigger joints pick a coarse sand with a larger grain size. Small joints need a smaller grain size. A rule of thumb is that the larger grains in the sand are no bigger than 1/3rd of the joint size.
You can replace the timber and bricks in the wall, but care is needed, especially in random rubble stonework, as it's normally less stable than brickwork.
When using a mortar dye, remember that it lightens over time.

Thank you Stuart! It's a bit of a minefield when moving away from modern gypsum based products in newer houses. Your help is much appreciated. The outside of the house has been rendered and I suspect with modern cement. I'm hoping that it doesn't have to all come off as well

 

[andy63]

That looks by the colour that ash may have been added to the mix. I'm no expert on the properties this bring and suitability but my external walls were pointed in this way assume in the victorian period and it held up ok despite it being covered in cement for 40 plus years.

Hi Itchinfilth! I wondered if it was ash in the mix. It is a very dull grey colour. Like your house, I think mine has been rendered externally with modern cement. I'm hoping that I don't have to take the whole thing back to stonework. The inside would need doing too, in that case. I've removed cement from a damp wall, upstairs and downstairs. I want to sympathetically restore as much as I can. It's amazing how the damp wall has dried out once I removed the plaster and cement. Thank you so much for your help

 

[Itchinfilth]

Hi Itchinfilth! I wondered if it was ash in the mix. It is a very dull grey colour. Like your house, I think mine has been rendered externally with modern cement. I'm hoping that I don't have to take the whole thing back to stonework. The inside would need doing too, in that case. I've removed cement from a damp wall, upstairs and downstairs. I want to sympathetically restore as much as I can. It's amazing how the damp wall has dried out once I removed the plaster and cement. Thank you so much for your help

Luckily it wasn't rendered externally but my forebears did cover most of the external walls internally in rock hard cement and concreted over the stone flags. All that has been removed at my sanities detriment!

 

[andy63]

I hope that I don't have to hack all the render off outside. Is it worth finding out? I think I'm worried about the answer to that

 

[alexander]

I hope that I don't have to hack all the render off outside. Is it worth finding out? I think I'm worried about the answer to that

in an ideal world for the best results it would be better for the moisture escape to the outside but its better to at least have one side of the wall breathable