What Is Rat Trap Bond: Wall Thickness, Size & Uses

Rat Trap Bond

Rat Trap Bond is also called the Chinese bond. It maintains a similar thickness as that of the brick laid by different methods. Rat Trap Bond Wall develops a complicated network of bricks inside the wall that generates the space in which the rats can be easily trapped so it is called Rat Trap Bond.

The main objective of utilizing this type of masonry bond is to decrease the number of bricks and amount of mortar required as compared to the English/Flemish bond.

What Is Rat Trap Bond?

Rat Trap Bond is a modular type of brick masonry bond in which the bricks are laid in a vertical position which creates a cavity in the wall while assuring the same wall thickness as in the case of the normal brick masonry wall. It is also known as a Chinese brick bond.

Rat trap bond wall is one of the wall methods of brickwork in wall construction. This method contains minor differences while placing bricks during brickwork; also, it works on a void-making principle.

It indicates there is space between the two blocks when placed on the layer. The bricks’ position in this procedure is vertical, so the brick face with fog remains remain the inner face where hollow space is generated due to the upright position of the bricks.

This kind of modern pattern of bricklaying was initiated by Mr. Laurie Baker in the 1970s in Kerala.

The main objective of this idea was to draw down the cost of the material in construction as much as possible moreover, parallel, it reduced material requirements, and similarly, also it gives great thermal efficiency when it compared to the older pattern of brick masonry.

The major thing that desire to note is that due to this method, the strength of the wall is not affected.

Rat Trap Bond Wall Construction Materials

The following are the materials used for the construction of the rat trap bond,

1. Bricks

The size of the bricks utilized must be of ordinary size and the difference in size is not obtained. The adequate sizes of brick in Indian scenarios are – Length 220 – 250 mm, Width 100 – 115mm, and Height 65 – 75mm.
The perimeters and corners of the bricks must be flat and sharp and perfectly rectangular in size.
Having a uniform size of bricks is vital as the masonry is the modular type and to obtain adequate strength and finish.
The bricks should have a compressive ratio as usual as the quality of the bricks should not degrade.

2. Mortar

The mortar should be mixed in a sufficient ratio of sand and cement as it plays an important role in the bonding of the brick.
The mortar should be mixed in a sufficient ratio of sand and cement as it plays an important role in the bonding of the brick.

3. Trowel

The trowel should be of a standard type for rat trap bonds.
It can be utilized for applying and spreading mortar.

4. Measuring Tape

The measuring tape should be standard and metallic having 5 m and 30 m in length.
It can be utilized for measuring the correct dimension.

5. Lining Thread

The lining thread is used to ensure a straight wall.

6. Wooden Template

The wooden template is used to prevent mortar from falling into the cavity.

Rat Trap Bond Construction

The procedure of the rat trap bond construction is as follows

The bricks are placed in a vertical direction so that the 110 mm face is seen from the front elevation, rather than the 75mm face. (considering brick of ordinary size 230 mm X 110 mm X 75 mm).
Rat trap bond wall thickness is 230 mm or 9″
As the width of the wall is kept as 230mm, a cavity is generated inside of the wall.
But, the first and the last layer of the brick masonry is created as the convention sold masonry.
In the sill, lintel and sides of openings are created of solid masonry (without cavity) for fixing frames.
To strengthen the brick masonry, vertical and horizontal reinforcement bars are contributed in the cavities.
Electrical conduits and plumbing pipes, with previous planning, can be settled inside the cavity for decent aesthetics.

Maximum Brick Wall Height Per Day

The extreme Rat Trap Bond brick wall height per day should not be over more than 9 layers. The added weight by each different bricklayer (course) required to be taken by the mortar.
The mortar however requires time to harden and to be able to hold a load of brick course without formulating cracks under the heavy load.
These cracks generally cannot be detected; still, they are there and will decrease the total strength of the masonry wall.

Curing of Rat Trap Brick Bond

A brick wall requires to be cured for at least 7 days. Many times a day, water requirements to be poured over the brick wall.
The walls are mainly very much uncovered to wind and sunshine and the moisture (water) of the wall will be dried out relatively quickly. Though, to gain the proper bearing strength, the mortar requires certain water content for hardening.

Pointing In Rat Trap Bond

The major purposes for pointing the surface of the brickwork or block joints are to enhance its weather resistance and to provide a neat finish to the work.
Pointing can be executed as construction of the brickwork proceeds, utilizing conventional mortar in which the bricks are bedded.
An additional method is to complete the masonry work first and then create the pointing work with a 1:2 cement mortar later.
The junctions must be raked out to the thickness of about 1 to 1.5 cm brushed, washed, and fill up with a 1:2 cement mortar.

Several Rules For Lying The Bricks For Rat Trap Bond

Layout of Rat Trap Bond — Bricks For Rat Trap Bond

1. Clean And Locate Corner

Always clear the surface where bricks are to be laid before
beginning the procedure. If any dirt existing between the plinth level
and brick masonry, the bonding of cement will be decreased and
occur in likely dampness and fix the corner of the wall.

2. The Layout

Two courses of bricks should place along with the wall line without
mortar by vacating a 1 cm gap for the mortar joint. Bricks
should be established such that simply shiner fit in there and
assure the brick cross is maintained.

3. Mortar Bed

After removing the dry layer, put the entire bed of mortar and
furrow it with the trowel.

4. Corner Bricks

The corner bricks will be carefully seated by laying all the
bricks with the frog inside the cavity wall to develop a
pleasing outer surface.

5. Mason’s Line

After completing the positions of corner bricks, fix the mason string at both sides of the wall put the top outside the perimeter of bricks to this line, and make sure the lower perimeter of brick is rapidly over the course below.

6. Fix Brick Cross

The first and second courses of brick should be put between
two corners without a vertical mortar joint. In addition, fill the mortar after properly placing the brick cross.

7. Laying Up Corner

Construct the corner of the wall after the first and second courses of brick are placed which should be generally five courses greater than the first course.

8. Mortar

The mortar should be applied simply to the top of bricks already laid for horizontal joints. Plywood template should be utilized while applying the horizontal joints to avoid the mortar falling into the wall cavity.

9. Use Of Level

Inspection with mason’s level for alignment after the laying course at the corner, bringing the corner is leveled and plumbed.

10. Laying Bricks Between Corner

Mortar should not be too far forward from the existing laying of
bricks to assure good bonding. Cut off the additional mortar with using
trowel and work back in new fresh mortar as each brick is laid.

Mason should work just from one side because it is not good that two masons work from two different sides as it might develop undesirable gaps that will be tough to close without distorting the exact bond.

11. Avoid Dead Mortar

Utilizing the dead mortar will weaken your cement-sand ratio and
may reduce the strength of the wall.

12. Top Layer

Later complete construction, close wall cavities within a top layer by lying with headers or rowlocks depending on the prefixed height of the completing wall.

Precaution While Constructing Rat Trap Bond

The following precautions should be taken while constructing rat trap bond masonry,

In the masonry work should be utilized only decent-quality bricks with no cracks should be utilized.
Specific care and supervision by an engineer should be executed
while constructing.
Skilled labor is required while constructing the wall.
An adequate mix of mortar should be conserved to hold the
bond tightly.
Inaccurate bricks with incorrect shapes and sizes which are not
straight and the ends of the brick not have sharp
edges should be ignored.
The frog of the brick should be overlooking the wall side.

Application Of Rat Trap Bond

The following are the rat trap bond applications,

It is an application for the structure where expenditure and energy conservation are complicated. Several of the applications of the rat trap bond are as follow:-
It can be utilized for low-cost construction because of the number of bricks and similarly the volume of mortar needed to establish the wall lessens.
It is utilized for buildings where thermal comfortability is to be conserved.
Wall having a thickness of 9” (approximate 23 cm) is relevant for utilizing a rat-trap bond.
It can be also utilized for low load-bearing walls up to three stories.

Rat Trap Bond Advantages

The advantages of rat trap bond brick masonry are as follows,

A few benefits are offered below. This method is flexible based on its limited consumption of construction material means it give benefits in material costing.
This method uses roughly 30% fewer bricks moreover 50% less mortar comparedd to regular masonry.
The number of bricks utilized in the building of rat trap bond masonry is 470 bricks, whereas, in common masonry, it is 550 bricks.
Many people ignore utilizing this method due to the unawareness of this method. However, the strength is as comparable as the earliest method of bricklaying.

If considering the major advantage of this method is thermal insulations, it is effective in reducing room temperature, and it decreases electricity costs.
This kind of bricklaying method plays an important role in withstanding heat and cold in both climate conditions.
This bricklaying pattern in the construction is eye-catching from both the inside and the outside of the wall; the plastering procedure is avoidable if it is not essential.
Well, this brick-laying method is similarly utilized in partition walls; further, even able to carry a load on it means its load-bearing capacity is not affected.
All vertical and horizontal reinforced bands, lintels (for common-size openings), and electrical lines are hidden inside the wall, occurring in a satisfactory aesthetic appearance without plastering (uncovered brickwork).
As this kind of masonry has 30% cavities, the dead load of the structure is decreased which in turn decreases the structure supporting units such as columns and footing.
This way is relatively beneficial in case of lessening material cost; It reduces material consumption, which outcomes in cost conservation in the construction budget.
In case of additional structural safety, reinforcement bars can be set through the cavity until the foundation.
Several buildings that were built decades ago have proved that this type of walling technology is strong and the maintenance expenses are low.

Rat Trap Bond Disadvantages

The disadvantages of rat trap bond brick masonry are as follows,

This kind of construction is not able to resist sound. Thus, the soundproof wall is not feasible this way.
Mason has to be careful while placing bricks. More care must be adopted while designing the wall length and heights for the structure.
Particular attention and care to be allotted while constructing and designing rat trap bond masonry.
Pre-training is needed if workers are not aware of this pattern of bricklaying, if not feasible, then employed experienced workers; hence the cost of a worker may rise.
As usual, a rat trap brick wall requires cleanness of the external surface (if not plastered) every three years.

Following Care Should Be Taken While Using Rat Trap Bond

First of all, the quality of bricks is always checked before utilized, quality with ordinary size, and even sharp perimeters.
The surface layer or primary bottom layer and last or topmost layer of the wall should be strong where no usage of vertical bricks.
Different areas like sill and lintel levels at the opening or sides of the opening have to be strong, so it is easy to contribute strength to fix frames for doors and windows.
If the building needs additional power then we can adopt reinforcement bars to set vertically at hollow spaces and corners and further at around openings of doors to resist earthquake impacts on the building.
In this case, advanced planning and creative work are needed to establish electrical appliances and plumbing pipes.
To sum up all aspects, this way of construction has an all-around cost in conserving on cost is about 25% of a utilized by building value by traditional 9-inch brickwork construction.
As per the investigation or analysis, 350 bricks per CFM in the old method, while in this rat trap bond method, it needed only 250 blocks; moreover, mortar consumption also reduced, so it impacts the building budgets instantly.

How to Use the Rat Trap Bond Method Practically

This method is less well-known due to people being familiar with the conventional way of brickwork. At current, these types of masonry construction are unique in several areas.

In this type of bricklaying pattern, bricks are situated on perimeters; hence face with fog remains inside of the wall, and it created a small rectangular section of four blocks.

Due to this, the wall has an inner void or free space, which plays an important role in getting significant thermal insulation inside the room area.

Summary:

Rat Trap Bond	Description
Definition	A brick masonry bonding pattern where the bricks are laid on their edge, creating a cavity or “trap” that provides thermal insulation and reduces material use.
Construction Method	Bricks are placed at a 45-degree angle, forming a cavity between them, which is filled with mortar to create a strong and efficient brickwork pattern.
Thermal Insulation	The cavity in the rat trap bond enhances thermal insulation, reducing heat transfer through the walls and contributing to energy efficiency.
Material Efficiency	Rat trap bond minimizes the use of bricks and mortar compared to traditional bonding patterns, making it a sustainable and resource-efficient construction method.
Structural Strength	The diagonal placement of bricks and the filled cavity contribute to the structural stability and load-bearing capacity of the wall.
Water Drainage	The vertical cavity allows for effective drainage of rainwater, preventing moisture-related issues and enhancing the durability of the structure.
Aesthetic Appeal	Rat trap bond can provide a distinctive and visually appealing pattern, adding an architectural element to the building’s facade.
Construction Advantages	Reduces material costs, improves thermal performance, and offers a unique aesthetic, making rat trap bond a sustainable and practical choice in construction.

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