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How to build a stone wall

How to build a stone wall

In the long and exciting daily process of building a green roof, each phase becomes a way of researching, thinking and experiencing construction, its steps and its techniques. After sharing our knowledge on the refurbishment of stone walls, we are now writing about our experiment (re)building one.   

A granite construction

Granite stone is an interesting ancient material that has different characteristics and advantages to use in construction: it’s a resistant and long-term material: it perfectly resists to time and weather constraints. Natural granite stone has one of the highest compressive strength in comparison to other materials. This resistance depends on the composition of the stone and the cover that may be applied on. To check the quality of your granite stones, take a look to see if you notice any dings, dents or scratches; and also check the porosity. A granite very porous or irregular will need regular coats of sealant. Granite has a good thermal phase shift (inertia): it stocks heat and restitues it slowly during the night; it’s sustainable when it is locally sourced. Furthermore, the stone can be directly reused from one construction to the other without any transformation.

Each type of stone offer nonetheless very different qualities.

TYPES OF STONEWEIGHT (kg/m3)COMPRESSIVE STRENGTH (MPa)WATER ABSORPTION (Percent by weight)
Granite2643 – 3204139 – 3090.002 – 0.2
Sandstone2242 – 264331 – 1081.5 – 6
Limestone2000 – 288019 – 1930.25 – 7.5
Marble2963 – 304393 – 1620.001 – 0.06
Slate2800 – 2880124 – 1850.15 – 0.25

Figure 1. Qualities of stones

If the stone type influences the visual and structural aspect of the construction, it also affects its final cost. The choice to work with granite is natural for us in this refurbishment project, as it is a common and local material in vernacular Portuguese architecture.

Phases and tools needed

The plan for the old stone walls’ construction is structured along three preparatory phases slightly similar to the ones mentioned in the refurbishment process to prepare the stones:

  • cutting the stones
  • cleaning and preparation of the stones
  • raising the wall itself, which includes as well the production of lime mortar (argamassa de cal in Portuguese) to fill the joints and bind recycled stones.

Before sharing our process, we remind the indispensable tools needed for each steps:

Figure 2. Cutting the stones
Figure 3. Preparing the stones
Figure 4. Argamassa de cal

Preparatory phases:

  • Chisels and hammers – indispensable tools to break and model the stones to raise the wall
  • Brushes – used to clean the stones and the further joints
  • String – simple and crucial tool to draw the direction lines of your future wall

Raising phase:

  • Mortar/concrete mixer – necessary to mix the lime mortar
  • Trowels – used to apply the mortar into wider joints
  • Wooden floats – useful for holding the mortar while you are handling the trowel
  • Buckets – to store your lime mortar as well as stones
  • Mash hammers – used to break up stones for pinnings
  • Plumb line – the check properly the verticality of the construction
  • Spirit level – to stabilise the level of the stones
  • Tape measure

Throughout each phase, we remind you that it’s important to protect your integrity using safety equipment correctly.
For these, you will need:

  • Scaffoldings
  • Helmets
  • Protective goggles
  • Appropriate protective gloves
  • Security shoes
  • Reusable dust masks

The raising process

There are two different techniques to build stone walls:

Figure 5. Dry stone wall

The dry stone wall: a technique that has been used since prehistory and doesn´t require to use any binding agent (mortar, earth, cob, …) to build the wall. The stones are wedged between each others.

Figure 6. Stone and mortar wall

The stone and mortar wall: as we experienced this technique to build a simple wall with lime mortar, the stones are laid out on top of each other with a binding agent.

A step by step guide

1. Planning the wall

First and foremost, before planning anything and depending on the scale of your project, make sure that you have a good ground foundation to build the expected wall. Check your soil properties and its loading capacities and most important find experts to advise and assist your project and its process. Once your project is defined, you can project the perimeter of your future wall by using strings.

2. Shaping the stones

Figure 7. Shaping the stones with chisel

Building a stone wall might become a puzzle game where stones need to be sized, shaped and adapted to the dimension of each other to fit. To shape your pieces, use a tape measure to plan your cut properly and one of the two following methods carefully.

  • Method A: the grinder

You can cut a stone with a grinder and a diamond cut blade. This method makes a clean, regular and precise cut. However, it creates a lot of dust, limits you by the size of the blade and creates a very slick surface on the stone. To allow the mortar to stick to it then on the wall, hammer the face of the stone to make it more irregular .

[ WARNING ] Safety first. As for any construction work, do not forget your safety equipment – goggles, gloves, dust mask and ear protection – and stay focused all the time you work. When you start noticing tiredness and distraction, take a break or simply finish your day.

  • Method B: the chisel

The chisel point is a safest and more traditional technique that we successfully experienced and learnt by watching videos to understand how to cut stone with hand tools. Follow these steps to achieve the same result :

To cut the stone
1. Make a straight line on your granite slab by holding the pitching tool (chisel) and hammer it at 45° angle (the angle can vary slightly) on the right place on the stone.
2. Repeat the process to obtain a cut line guide.

You will finally cut the stone and reach the expected result by repeating the operation.


To flatten the surface
To flatten the surface, use a similar method step by step and with a lot of patience:

1. Locate three points that are on the level that you want to reach.
2. Link these points (use a small flat chisel).
3. Move from the inside to the outside with a bigger chisel.

We noticed, as indicated in our previous investigation, that the small chisels are better for the rough work, and the big ones for the fine work.

3. Laying the stones

Once you have planned the whole, washed the stones to remove the dust and optimize the grip of the mortar, it’s time to start your construction and put the wall all together. To ensure the planarity of a straight and vertical wall, use a plumbline and a spirit level during all the process. Then, layer by layer, following these next steps:

  • Put the first stones of your wall and try to understand how to work with balance. Even without the mortar, the stones should stand and fit properly. Place the flatter size of the stone for the upper side. You will obtain then a plain area to start the following layer.
  • Once the base is done, raise your wall layer by layer using mortar to bind the stones.
  • Fill the joints first with mortar, then with small stones and again with mortar to ensure that the whole is well linked. For this step, do not forget to cross the joints.
  • After the curing time, clean your joints with a wire brush to check if they are correctly applied.

The building technique, the surface, the colour and the type of mortar used will impact on the look of the finished wall. But in any case, the structural quality of your work is the most fundamental point.

Last useful hints: if your futur wall is an extension of an existing wall, hammer a bit the face of the stones to get a rougher surface that will stick better to build your wall. In a case like this, ask your engineer if you need to add for example a metal clamp reinforcement to link the two parts of the wall.

Figure 8. Clamp reinforcement

In addition, to move heavy stones around, we investigated techniques to solve this challenge:

  • Flip and roll the stone as much as you can.
  • A wheelbarrow is useful when you need to transport a stone far away.
  • Use a crowbar, for example, to help you to get a greater lever arm and move a bit your stone, and gradually lift and move the stone.

Finally, use your brain before your arms and back. Now raise your stone walls and stay tuned for our next article!

Sources:

[1] Stone specialist. “Building with stone: Granite (Part1)” [Online] Available at: https://www.stonespecialist.com/news/stones-quarries/building-stone-granite-part-1 (Last accessed: April 2019).

[2] B&Q. “How to build a stone garden wall” [Online] Available at: https://www.diy.com/ideas-advice/how-to-build-a-stone-garden-wall/CC_npci_100137.art (Last accessed: April 2019).

[3] MC Groarty, M. (2019). “How to move a heavy rock without hurting your back” [Online] Available at: http://freeplants.com/rock-moving.html (Last accessed: April 2019).

[4] The Stone Trust: “How to build walls” [Online] Available at: https://thestonetrust.org/resource-information/how-to/ (Last accessed: April 2019).

[5] Bloom, D. “Basic guide to stone foundations” [Online] Available at: http://stonehengemasonry.ca/stone-foundations-basic-guide/ (Last accessed: April 2019).

[6] Quora. “How do I check quality of granite slabs?” [Online] Available at:https://www.quora.com/How-do-I-check-quality-of-granite-slabs (Last accessed: April 2019).

Figures:

Figure 1. “Properties of Stones”. [Online] taken from:
https://images.slideplayer.com/19/5735952/slides/slide_37.jpg

Figure 5. Robert Grant, “Muro em granito”, in Santiago de Besteiros, Tondela, Portugal, 12/10/2008. [Online] taken from: https://farm4.staticflickr.com/3051/2961389684_574b7705a7_b.jpg

Figure 8. Nerijp, “Agrafe reliant deux blocs de pierre”, Juin 2010. [Online] taken from:
https://upload.wikimedia.org/wikipedia/commons/3/3c/Agrafe-mur2.JPG

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