Rat Trap Bond
The rat trap bond (RTB) was first introduced by eminent architect Laurie Baker in India and supported by HUDCO.
In the RTB bricks are placed on edge in 1:6 cement mortar. With this technique there is reduction in cost of the wall by 25%, as with conventional English bond (9’’thk wall) 350 bricks are required per cu. m whereas in Rat-trap bond only 280 bricks are required and also the reduced number of joints reduces the mortar consumption. No plastering of the outside face is required and the wall usually is quite aesthetically pleasing and the air gaps created within the wall help make the house thermally comfortable. In summer the temperature inside the house is usually at least 5 degrees lower than the outside ambient temperature and vice versa in winter.
The main features of Rat-trap bond wall are:
• Strength is equal to standard 10" (250mm) brick wall, but consumes 20% less bricks.
• The overall saving on cost materials used for construction compared to the traditional 10" wall is about 25%.
• The air medium or cavity created in between the bricklayers helps in maintaining a good thermal comfort inside the building. This phenomenon is particularly helpful for tropical climate of South Asian and other countries.
• As the construction is done by aligning the bricks from both sides with the plain surfaces facing outwards, plastering is not necessary except in a few places. The finished surface is appealing to the eye from both internally & externally,
• Buildings up to two stories can easily be constructed with this technique. Mr. Laurie Baker has pioneered this type of construction and had built such houses more than 40 years ago without having any signs of distress till now.
• In R.C.C. framed structures, the filler walls can be made of rat-trap bond.
• Due to lesser load on the base of the walls, the width of foundation is also decreased, resulting in a saving of about 8% on use of bricks, cement and sand in foundation and plinth.