Stone masonry is a traditional construction method where stones are bonded with mortar to create solid, durable structures. One critical application of stone masonry is in footings—structural foundations that support walls and distribute loads to the soil. This article explores the purpose, materials, and construction techniques involved in stone masonry footing.
Purpose of Stone Masonry Footing
The primary purpose of stone masonry footing is to support structural walls and safely transfer their load onto the ground. Stone masonry footings need to be stable, resistant to settlement, and prevent sinking over time. An ideal stone masonry footing also directs the load vertically to prevent any lateral forces that could lead to structural instability.
Construction of Stone Masonry Footing
Constructing a reliable stone masonry footing involves a few essential steps, including excavating an adequate trench, selecting appropriate materials, and using suitable bonding agents. Each phase is critical to the durability and load-bearing capacity of the finished structure.
Excavation for Stone Masonry Footing
Dimensions of Excavation
Before beginning the foundation, a trench must be excavated to a depth of about 1 to 1.5 meters. The width of this trench depends on the load the footing will bear and the properties of the soil at the site. Once the trench is complete, the soil at the base should be compacted to improve stability and load distribution.
Preparation of Excavated Soil
Proper compaction of the soil at the trench’s bottom ensures that the soil does not settle later, which could jeopardize the footing’s stability. With a compacted base, the trench is ready for the next stage of construction.
Properties and Selection of Stones for Footing
Selecting suitable stones for stone masonry footing is crucial to its longevity and load-bearing capacity. Stones should meet the following criteria:
- Durability: Stones should withstand weathering and degradation.
- Absence of Cracks and Cavities: Stones must be solid and free from internal weaknesses.
- Hardness and Toughness: Stones need to be hard enough to resist pressure and other physical stresses.
Types of Suitable Stones
The best choices for stone masonry footings include granite, hard laminated sandstone, limestone, and bluestone. Each of these types offers the necessary durability and strength for long-lasting footings.
Dimensions and Preparation of Stones
Desired Dimensions of Stones
The thickness of each stone should ideally be one-fourth of its width. If possible, the width of the stone should match the footing’s width. In cases where such large stones aren’t available, it’s acceptable to use smaller stones with joints that are properly bonded with mortar.
Preparation of Stones
To ensure that stones bond well with the mortar, they should be adequately wetted before placement. This prevents the stone from absorbing moisture from the mortar, which could weaken the bond over time.
Concrete Mix for Plain Concrete Bed
The bottom of the trench should be lined with a plain concrete bed, which acts as a stable, load-distributing base. The concrete mix is typically one part cement, four parts sand, and eight parts coarse aggregate, with a maximum aggregate size of 40 mm.
Dimensions of Concrete Bed
The concrete bed should be between 10 and 15 cm thick, and it should extend about 15 cm beyond each side of the footing. This extension adds an additional 30 cm to the width, ensuring stability across the foundation.
Mortar Ratio and Use in Stone Masonry Footing
Mortar plays a vital role in bonding stones together and sealing joints to prevent water penetration. The recommended mortar ratio for stone masonry footing is one part cement to six parts sand. This blend creates a firm, water-resistant bond suitable for heavy structural loads.
Construction Steps for Stone Masonry Footing
The following steps outline the construction process for stone masonry footing:
- Prepare the Plain Concrete Layer: Once the trench is ready, pour a layer of plain concrete at the bottom to serve as a foundation bed.
- Lay the First Course of Stones: Place a layer of mortar on the concrete bed and begin laying the first course of stones. Ensure stones are placed close to one another, maintaining a maximum joint width of 2 cm.
- Arrange the Joints: To prevent weak spots, stagger the stone joints rather than aligning them vertically, which could create potential failure points.
Joints Arrangement and Bonding
In stone masonry, long vertical joints weaken the structure. Instead, arrange stones to create staggered joints, ensuring even load distribution and structural integrity.
Placing Bond Stones for Strength Enhancement
Bond stones are vital for reinforcing the footing. Placed at intervals of approximately 1 meter, these stones penetrate the full thickness of the masonry, enhancing cohesion and stability.
Bond Stone Length Adjustment
For thicker footings, it’s necessary to extend bond stones to ensure they achieve the desired reinforcement effect. Overlapping multiple bond stones can achieve the required length and strength in thick footings.
Use of Heart Stones in Stone Masonry Footing
Heart stones are smaller stones placed at the center of the footing to fill voids and strengthen the structure. By placing heart stones close together, builders can eliminate gaps, reducing weak points in the foundation. These stones should be covered with mortar to further increase footing strength.
Conclusion
Constructing a solid stone masonry footing requires careful attention to excavation, stone selection, mortar use, and layering techniques. By following the outlined steps and choosing durable materials, builders can create footings that provide essential support to structural walls without settling or sinking over time. The result is a reliable and long-lasting foundation that upholds the principles of traditional stone masonry while meeting modern construction standards.
This article provides an in-depth look at the materials, methods, and considerations involved in constructing a sturdy and reliable stone masonry footing.