Masonry Repair and Strengthening Techniques: A Comprehensive Guide

Posted on May 4, 2024 in Technology

Masonry Repair Techniques

Drilling and Plugging

The drilling and plugging method is suitable for repairing cracks that run in reasonably straight lines and are accessible at one end. This involves drilling along the length of the crack and grouting it to form a key using precast concrete or mortar plugs set in bitumen. The bitumen serves to break the bond between the plugs and the hole, preventing the plugs from cracking due to subsequent movement of the opening. For an enhanced seal, a second hole can be drilled and plugged with bitumen alone, using the first hole as a key and the second as a seal.

Reinforced Concrete Jacketing

Reinforced concrete jacketing involves restoring or increasing the size of an existing structural member by encasing it with suitable materials. The process enhances the load-carrying capacity and stiffness of the structure. However, it results in an increase in the size of the concrete member after jacketing and requires constructing new formwork, which are the main disadvantages of this method.

Creating New Openings in Masonry Walls

General Procedure

1. Determine if the wall is load-bearing or not.
2. If load-bearing, set up temporary support to carry weight from above.
3. Protect the floor from damage.
4. Measure and mark the new opening’s position.
5. Outline the lintel opening, ensuring it extends at least 150mm beyond the door frame.
6. Erect scaffolding and temporary props as required.
7. Place the lintel within the temporary supports before securing them.
8. Use appropriate tools to cut the opening, considering safety and cleanliness.
9. Position the lintel, ensuring it extends adequately beyond the opening.
10. Fill gaps and voids around the lintel securely.
11. Insert insulation if the wall is external.
12. Once the lintel is set and mortar cured, cut the opening.
13. Carefully remove bricks below the lintel.
14. Place the frame securely within the opening.
15. Complete any necessary finishing touches such as plastering and painting.
16. Tidy and clean the work area thoroughly.

Scheme of Work Steps for Forming New Opening and Wall Removal

1. Preparation Works:

1. Measure the position of the new door opening.
2. Mark the position for the new lintel.
3. Secure metal props.
4. Make the right distance for lintel manipulation.
5. Make holes in the existing wall.
6. Thread the needles through the holes and secure them on props.
7. Remove slack from the supporting system.

2. Lintel Opening Excavation:

1. Remove plaster from one side of the wall.
2. Remove bricks of the masonry.
3. Make a hole for a lintel.
4. Insert two lintels.
5. Make sure the lintel is level.
6. Repeat the first 5 steps for the other part of the wall.
7. Fill the voids with cement.

3. Door Opening Excavation:

1. Remove the lintel, props, and needles.
2. Remove the bricks from below the lintel.
3. Remove bricks from top to bottom.
4. Fill the holes with cement.
5. Apply new plaster.

4. Finishing Works:

1. Install the frame.
2. Paint.
3. Install skirting.

Removing Load-Bearing and Non-Load-Bearing Walls

Load-Bearing Walls

If it is possible to work on the upper floor:

Using temporary timber propping with offset posts, new lintels are made of rolled steel joists (RSJ) and located at the level of the floor structure. They provide definitive support. Joists are two-sided, extended by additional short timber beams. Temporary propping is made of rolled steel joists (RSJ).

If it is not possible to work on the upper floor:

When removing a load-bearing wall, the new steel beam will have to rest on something. New lintels are made of rolled steel joists (RSJ) and located under the floor structure. They provide definitive support. Temporary propping is made of timber.

Non-Load-Bearing Walls

If it is possible to work on the upper floor:

• Using temporary timber propping to support the partition.
• Using temporary propping made of rolled steel joints (RSJ) located on the upper floor.
• The partition is supported only by finally fitted lintels made of rolled steel joists (RSJ) located on the upper floor.
• The partition is supported only by fitted lintels made of rolled steel joist (RSJ) located in the floor structure.
• The partition is supported only by finally fitted lintels made of rolled steel joist (RS) located in the floor structure.

If it is not possible to work on the upper floor:

• Using temporary timber propping to support the partition.
• Using temporary propping made of rolled steel joist (RSJ) to support.
• The partition is supported only by finally fitted lintels made of rolled steel joist (RSJ).

Lintel Types, Methods, and Dimensions

For larger openings, lintels made of a steel beam (rolled steel joist) are typically used. Another type could be a precast concrete lintel.

Methods:

• Installing the lintels first from one and then from the other side of the wall.
• Installing the lintels first from one and then from the other side of the wall, and an inner beam is inserted.

Dimensions:

The steel beam must have at least 100mm end bearing and be seated on padstones. It should be seated on a large piece of load-bearing masonry with a plan area of bonded masonry of at least 0.1m2. It should not be inserted into a chimney and should not be within 50mm of a flue.

Temporary Supporting Structures

Propping is a provision of vertical supporting to a building or structure. Types:

• Acrow props (adjustable steel props)
• Proprietary horizontal steel frames (no more props)
• Strongboys (steel plates)

Masonry Strengthening Techniques

Repointing of Masonry Walls

Repointing is the refilling of the outer part of mortar joints between masonry units where the previous mortar has weathered away or has been removed because it is unsuitable. It can affect the look and durability of masonry.

Helical Stainless Steel Reinforcing Bar

Helical stainless steel reinforcing bars combine great axial strength with flexibility and accommodate differential building movement. Some of the most commonly occurring structural faults that can be repaired using helical stainless steel reinforcing bar include:

• Repair of bay windows
• Repair of brick arch lintels
• Repair of cracks near corners and openings
• Stabilizing bowed walls into joist sides
• Reconnecting internal walls with external walls
• Replacing cavity wall ties
• Crack stitching
• Creating masonry beams
• Repairing or creating flat arch lintels
• Overcoming foundation settlement

Masonry Vault Arch Failures

Main Causes:

• Excessive load
• Loss in load-bearing capacity of side walls, causing the vault to lose its support and decline

Foundation Repair Techniques

Underpinning Methods

• Cantilever needle beam method: An extension of the pit method, used if the plan possesses a stronger interior column.
• Pier and beam underpinning method: The size and depth of the beams are based on the ground conditions and applied loads.
• Pile and beam underpinning: Piles are installed beside the walls, and beams are inserted to join the tops of the piles.
• Mass concrete underpinning method (pit method): To prevent fracture, damage, or settlement of the wall being underpinned, the work should be carried out in short lengths called legs or bays.

What is Underpinning?

Underpinning is a method for repair and strengthening of building foundations. The main objective of most underpinning works is to transfer the load carried by a foundation from its existing bearing level to a new level at a lower depth.

Mini Piles

Mini piles can be implemented where the loads from the foundation have to be transferred to strata located at a distance greater than 5m. This method is adaptable for soil that has a variable nature, access is restrictive, and causes environmental pollution problems. Mini-piles are also used in some methods, such as needle and pile underpinning and root pile or angle piling.

Timber Structure Strengthening Techniques

Common Methods:

• Concrete slab: Casting a concrete slab on a timber floor while assuring a proper connection between concrete and timber beams creates a composite system that takes the best profit from both materials. The concrete slab is stressed to compression while the timber beams work in tension.
• Fiber reinforced polymers (FRPs): FRPs can be bonded anywhere around or inside cut slots inside beams. Reinforcements subjected to compression are better used inside slots opened in the timber beams to avoid element instability.
• Steel bars, plates, or profiles: These can be added or inserted on any side of a timber beam to increase its carrying capacity. They can be applied to the tension zone and the compression zone. With plates or profiles bonded to the surface, the connection is done with steel bolts, studs, or dowels, while insertions of bars are bonded with epoxy resin.
• Timber elements: This is done by adding new timber elements to the original beam, connecting both members using traditional timber carpentry or steel connectors.

Repair of Timber Beam Damaged Extremities