ᐅ Pointing and Plastering of Interior Natural Stone and Rubble Stone Walls
Created on: 20 Oct 2012 20:59
R
roberto413R
roberto41320 Oct 2012 20:59Hello
I am Roberto and recently became a homeowner. I have a few questions about mortaring/plastering natural/rough stone walls on the interior. Perhaps some of you have experience with this or even tips for me.
A few details about the building:
The exterior walls of the building are constructed from natural/rough stones, and the interior partition walls are made of simple bricks. The house was built around 1900 and renovated in 2000 with new exterior plaster and a new roof.
Inside, nothing has been done since about 1960. The plaster had significant cracks and I have already completely removed it. The plaster was a lime/sand mix with some kind of binder.
The now visible natural/rough stones were originally mortared with lime/sand mortar but are now only loosely stacked, which is a major problem for me.
The walls are nearly 60cm (24 inches) thick but lack stability; it is absolutely impossible to fix anchors for radiator brackets or kitchen cabinets!
The old mortar has turned to dust, and after chiseling and brushing with a stiff street/metal broom, I now have joints and holes more than 10cm (4 inches) deep caused by fallen stones/infill pieces.
My question is: What material is best for filling or re-mortaring these joints? In areas around heating pipes (which will be surface-mounted later), radiator brackets, and window recesses, I have used a sand/cement mix (4:1 ratio with well-washed sand). According to online forums, guides, and information sites, this is not correct because the cement mix is too hard and can damage the wall over time. Cement is said to prevent the wall from “breathing” and is too rigid.
Many forums and guides mention using trass cement for natural or rough stone walls, but according to what I have read, this is only necessary to prevent efflorescence and weathering on freestanding stone walls. Others recommend the traditional method of working with air lime and sand, but how do those builders achieve solid adhesion in their constructions?
Friends and acquaintances recommended some local building companies, which I invited to submit a quote on site. The builders proposed applying a spray mortar in a mesh pattern and then plastering the walls with two layers of lime/cement plaster.
This proposed solution makes me skeptical. On one hand, cement is labeled as harmful, but on the other hand, they suggest using a cement-based scratch coat and lime/cement plaster to fix the issue?
I also doubt that pure lime/cement plaster will provide the stability I want in the deep joints.
Then there is the question of wall breathability, which I can only partly imagine with lime/cement plaster. Wouldn’t this cause moisture buildup inside the walls because this type of plaster does not absorb and release humidity well? Due to the deep joints, the plaster layers will be quite thick, and in my opinion (as a layman) this will neither allow the wall to breathe nor provide much strength (for anchors and so on). Also, the large amount of material required will result in a high final cost. According to the building companies, it is not possible to have a crack-free wall over time on these substrates.
I also have a question regarding the wall’s breathability: Does the plaster breathe or does the wall/masonry itself? In my profession (industrial assembler), I work daily with reinforced concrete buildings; nothing breathes there either, and everything is regulated by the plaster (usually gypsum plaster).
What would be the best material to fill the deep joints in the natural/rough stone walls, and which type of plaster would be most suitable?
I am grateful for any help!
Best regards, Roberto
I am Roberto and recently became a homeowner. I have a few questions about mortaring/plastering natural/rough stone walls on the interior. Perhaps some of you have experience with this or even tips for me.
A few details about the building:
The exterior walls of the building are constructed from natural/rough stones, and the interior partition walls are made of simple bricks. The house was built around 1900 and renovated in 2000 with new exterior plaster and a new roof.
Inside, nothing has been done since about 1960. The plaster had significant cracks and I have already completely removed it. The plaster was a lime/sand mix with some kind of binder.
The now visible natural/rough stones were originally mortared with lime/sand mortar but are now only loosely stacked, which is a major problem for me.
The walls are nearly 60cm (24 inches) thick but lack stability; it is absolutely impossible to fix anchors for radiator brackets or kitchen cabinets!
The old mortar has turned to dust, and after chiseling and brushing with a stiff street/metal broom, I now have joints and holes more than 10cm (4 inches) deep caused by fallen stones/infill pieces.
My question is: What material is best for filling or re-mortaring these joints? In areas around heating pipes (which will be surface-mounted later), radiator brackets, and window recesses, I have used a sand/cement mix (4:1 ratio with well-washed sand). According to online forums, guides, and information sites, this is not correct because the cement mix is too hard and can damage the wall over time. Cement is said to prevent the wall from “breathing” and is too rigid.
Many forums and guides mention using trass cement for natural or rough stone walls, but according to what I have read, this is only necessary to prevent efflorescence and weathering on freestanding stone walls. Others recommend the traditional method of working with air lime and sand, but how do those builders achieve solid adhesion in their constructions?
Friends and acquaintances recommended some local building companies, which I invited to submit a quote on site. The builders proposed applying a spray mortar in a mesh pattern and then plastering the walls with two layers of lime/cement plaster.
This proposed solution makes me skeptical. On one hand, cement is labeled as harmful, but on the other hand, they suggest using a cement-based scratch coat and lime/cement plaster to fix the issue?
I also doubt that pure lime/cement plaster will provide the stability I want in the deep joints.
Then there is the question of wall breathability, which I can only partly imagine with lime/cement plaster. Wouldn’t this cause moisture buildup inside the walls because this type of plaster does not absorb and release humidity well? Due to the deep joints, the plaster layers will be quite thick, and in my opinion (as a layman) this will neither allow the wall to breathe nor provide much strength (for anchors and so on). Also, the large amount of material required will result in a high final cost. According to the building companies, it is not possible to have a crack-free wall over time on these substrates.
I also have a question regarding the wall’s breathability: Does the plaster breathe or does the wall/masonry itself? In my profession (industrial assembler), I work daily with reinforced concrete buildings; nothing breathes there either, and everything is regulated by the plaster (usually gypsum plaster).
What would be the best material to fill the deep joints in the natural/rough stone walls, and which type of plaster would be most suitable?
I am grateful for any help!
Best regards, Roberto
Hello Roberto,
- The entire structure "breathes" – including your reinforced concrete (but very little); this refers to the wall’s moisture absorption and release, and only marginally relates to air exchange.
- Since the bricks were laid with lime mortar, you should also fill the joints with it. However, you can make the top joint (the last 3 centimeters (1 inch)) a bit firmer (e.g., 6/2/1 sand/pozzolanic lime/pozzolanic cement) because there is little moisture exchange there. The mortar just needs to be softer than the stone to compensate for "movement" and pressure. The pozzolan is also important inside; otherwise, your plaster will develop salt efflorescence. Alternatively, you can use firmer joints only where you want to hang something or attach fixtures outside the joints.
- If you want to plaster the walls, I would recommend either a pure lime plaster or a clay plaster (which creates a great indoor climate). Of course, with these you still cannot hang anything on the plaster.
- That leaves only two practical options:
1. Installing a drywall partition or
2. Adding an additional masonry layer
Both require space, but by choosing the right type of brick, you can significantly reduce your energy costs.
I hope this helps you at least a little.
Greetings from Berlin
Thomas
- The entire structure "breathes" – including your reinforced concrete (but very little); this refers to the wall’s moisture absorption and release, and only marginally relates to air exchange.
- Since the bricks were laid with lime mortar, you should also fill the joints with it. However, you can make the top joint (the last 3 centimeters (1 inch)) a bit firmer (e.g., 6/2/1 sand/pozzolanic lime/pozzolanic cement) because there is little moisture exchange there. The mortar just needs to be softer than the stone to compensate for "movement" and pressure. The pozzolan is also important inside; otherwise, your plaster will develop salt efflorescence. Alternatively, you can use firmer joints only where you want to hang something or attach fixtures outside the joints.
- If you want to plaster the walls, I would recommend either a pure lime plaster or a clay plaster (which creates a great indoor climate). Of course, with these you still cannot hang anything on the plaster.
- That leaves only two practical options:
1. Installing a drywall partition or
2. Adding an additional masonry layer
Both require space, but by choosing the right type of brick, you can significantly reduce your energy costs.
I hope this helps you at least a little.
Greetings from Berlin
Thomas
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