Here are common fixing methods used in stonemasonry with limestone and sandstone:

1. Mortar Bedding:

• Description: Traditional fixing method where a mortar bed is used to attach stone blocks or slabs to each other or to a substrate (like a wall or foundation).
• Type of Mortar: Typically, a lime-based mortar or cement-based mortar is used, depending on the specific requirements of the project. Lime mortar is often preferred for historic buildings because it allows for flexibility and breathability, which is important for soft stones like limestone and sandstone.
• Application: The stone is placed into the mortar bed, and the mortar fills in the gaps between the stones, creating a strong bond.

2. Mechanical Fixings (Metal Fasteners):

• Description: Metal anchors, bolts, or clips are used to secure stones to a structure. This is often done in modern construction or restoration work to provide extra support.
• Types of Fasteners: Stainless steel or brass anchors, dowels, and clips are typically used to minimize corrosion. These fasteners can be embedded into the stone using holes drilled into the stone (careful drilling is required to avoid cracking).
• Application: The stones are drilled to accept these fasteners, which are then attached to a metal frame, wall, or other structural elements.

3. Stone Dowel Fixing:

• Description: This involves drilling holes into both the stone block and the supporting substrate, then inserting a stone dowel (typically made from a harder stone like granite or a metal dowel). This technique is especially useful for large or heavy blocks.
• Application: After aligning the blocks, dowels are inserted, helping to prevent movement and maintaining the integrity of the stonework.

4. Reinforced Masonry:

• Description: For walls or larger structures, reinforcing steel bars (rebars) may be embedded into the mortar or the stone blocks themselves, providing additional stability.
• Application: This is especially useful for limestone or sandstone facades, where the surface may be prone to cracking or where seismic activity or other forces might be a concern.

5. Adhesive Bonding:

• Description: Special adhesives or epoxy resins may be used for smaller repairs or installations, particularly when working with slabs or thin veneer stone.
• Types of Adhesives: Two-part epoxy or polyurethane resins may be used to bond stone elements.
• Application: This method is less common for structural work but may be used for decorative elements, interior applications, or thin stone cladding.

6. Pointing:

• Description: While pointing primarily refers to the finishing technique for the joints between stone blocks, it also plays an important role in fixing the stonework in place. The mortar used for pointing helps hold the stone elements together while providing a weatherproof seal.
• Application: The mortar is pressed into the joints between the stones, ensuring they remain fixed in place and that no gaps or movement can occur.

7. Anchoring with Dowels and Adhesive (Combination):

• Description: This hybrid method involves the use of both dowels and adhesives to securely fix a stone in place. It’s commonly used in situations where mechanical stability and an invisible or seamless bond are required.
• Application: After inserting dowels into drilled holes, a strong adhesive can be used around the edges to reinforce the connection, ensuring a durable and aesthetically clean bond.

Considerations for Limestone and Sandstone:

• Fragility: Both limestone and sandstone are more porous and softer compared to harder stones, so excessive force during fixing (e.g., over-tightening bolts) can cause cracking or damage.
• Moisture Sensitivity: These stones can absorb moisture, which may weaken the fixing over time if the wrong type of mortar or adhesive is used. Lime-based mortars allow for some moisture movement, which is beneficial for these materials.
• Weathering: As sedimentary stones, limestone and sandstone are prone to weathering, so using a breathable, flexible fixing system (e.g., lime mortar) helps prevent long-term degradation.
• Aesthetic Considerations: When fixing stone, the method should take into account the aesthetic impact, especially for historical or decorative stonework. For example, metal fasteners may be hidden behind the stonework, or mortars may be selected to match the color of the stone.

In summary, stonemasonry fixing techniques for limestone and sandstone involve a combination of traditional methods like mortar bedding and modern approaches like mechanical fasteners or adhesives. Careful consideration of the stone's fragility and porosity, as well as the long-term durability of the fixing method, is key to ensuring the structure's integrity.