Why Brick Bat Coba Not the Correct Method for Terrace Waterproofing?

India is having more than 4000 kms of coastal line. Generally, these coastal areas receive more than average rainfall in the rainy season. The homes in these coastal areas are, therefore, more prone to leakages from terrace and walls. This not only led to peeling of paints and ruining the interiors but also led to growth of fungus. Such unhygienic conditions can be detrimental to the health of families living in these houses.

So, how can we tackle such severe leakage issues? In India, terrace waterproofing has always been done with very traditional materials. Typical conventional systems like brick bat coba, Lime terracing or the "Mud Fuska" technique are still very much prevalent. These systems are supposed to be offering terrace waterproofing solution with some insulation against heat.

The brick bat coba is used particularly for waterproofing of flat roofs, primarily RCC with some thermal insulation (mud phuska) in the coastal region. It consists of putting brick bats on roofs, to give a slope and then grouting the same with mortar admixed with various proprietary chemicals most in the nature of waterproofing compounds. In the new construction house, it provides an excellent slope in a moderate cost, so that the water drains away.

Though this conventional way of terrace waterproofing is prevalent, it is not a correct way of terrace waterproofing method, it just gives slope to terrace to drains away the water accumulated on terrace. Over the years, it has been followed and believed to be the most trusted waterproofing system which unfortunately is not true. Many times, it is said that it provides heat insulation which is also not true. This claim can’t be quantified as it is not measurable. Moreover, it has been observed that the coba surface attains the same temperature as the bare cement slab during the peak hours in summer.

This conventional method has severe following limitations, hence it can’t be called as a waterproofing method.

Imposes Unnecessary Load

This system has the disadvantage of imposing an unnecessary load on the system. The thickness of the coba is maintained at about 125mm to 150mm which adds unnecessary dead load on the slab. Once cracks appear, they are almost impossible to repair and water as in the case of the tar felting travels below the coba and exits wherever it finds a path. It is impossible to trace the inlet point and let alone repair it.

Cracks Reappeared Due to Temperature Variations

The brick bat coba system is a rigid one and cannot accommodate the movement due to thermal stresses. This leads to development of cracks. The brick bat coba treatment, though successful in the damp heat of coastal regions, cracks up completely on contact with the variations of temperature faced in North India between day and night temperature.

Damages Mother Slab

Some parts of the coba stick so well to the concrete that even if an attempt is made to dismantle the system the mother slab gets damaged.

Bricks Act as Water Reservoir

The bricks used in the system are porous and when water enters, these bricks readily absorb and hold large amount of water creating a sort of reservoir above the slab. The bricks used in BBC is usually of not a good quality hence over a period of time they absorb water and become loose and give way to more leakages.

Creates Noise, Debris

The coba adheres firmly to the slab and the usage of chisels and hammers can create cracks on the slab, aggravating the problem rather than resolving the same. The disposal of the debris from the dismantled system is yet again a cumbersome issue. Re-laying of the similar brick bat coba again is certainly not the answer to this problem.

Lack of Skilled Manpower

These days due to lack of skilled manpower and lack of attention to detail, rainwater seeps through the cracks in the brick bat tiling and collects under the mud phuska causing seepage into the RCC roof. In order to repair this, all layers of the roof have to be opened up and waterproofing layer redone. This causes hardship to the user apart from cost related issues.

The experts in the field of Construction Industry validates these points. Says consultants from Gherzi Eastern and DCL:

• Brickbat coba will have lot of surface cracks and hence it is not a waterproofing system.
• The quality of bricks used in BBC is usually not good hence over a period of time they absorb water and become loose and give way to more leakages.
• Brick bat coba should not be confused for waterproofing. It is a good weather proof layer.

Mr. Rohit Krishan Gulati, Principal Architect, Incubis Consultants (I) Private Limited, New Delhi writes, "this process works well when the quality of work- manship is high and the masons are well experienced in taking care of the details and jointing etc. But there is lack of skilled labor and lack of attention to detail. So the system gets failed miserably."

Dr. Fixit Institute of Structural Protection & Rehabilitation, a not-for-profit organization confirms that hardly anybody uses such method of brick bat coba for terrace waterproofing internationally. The best practice used internationally is to coat the terrace with elastomeric coatings. These coatings has certain definite advantages over conventional brick bat coba method.

• It does not impose any unnecessary load on mother slab, as it just a coating of 300-400 microns.
• These coatings has high crack bridging ability. As it is elastic in nature, it can accommodate the movements due to thermal stresses.
• It can be easily applied by brush or roller, so it does not damage mother slab while application.
• It does not create any noise, debris while application. It can be applied over existing brick bat coba, without dismantling the same.
• If any of the patch is damaged by some reason, it can be coated with ease again.
• This method ensures the waterproofing of terrace in much less time as compared to brick bat coba.
• It lasts for 5 years without any hassles.