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Roof Waterproofing By Brick Bat Coba

Roof Waterproofing By Brick Bat Coba

By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

INTRODUCTION
Waterproofing is a treatment of a surface or structure to prevent the passage of water under hydrostatic pressure. Waterproofing barrier system may be placed on the positive or negative side. Damp proofing is a treatment of a surface or structure to resit the passage of water in the absence of hydrostatic pressure. A damp proofing barrier system is used to perform the same functions as a waterproofing system but cannot be used to protect against water pressure. Water may be forced through building members by hydrostatic pressure, water vapour gradient, capillary action, wind-driven rain, or any combination of these. This movement is aggravated by porous concrete, cracks or structural defects, or joints that are improperly designed or installed. Leakage of water into structure may cause structural damage, and invariably cause damage to the contents of the structure.

New roofs RB or RCC slabs must be constructed specified by the designer. Roof waterproofing is a widely misunderstood subject. Often inadequate attention given during the construction of RB or RCC roof slab, wrong products used for waterproofing and generally insufficient treatment given, lead to leakage. Movement because of structural deflection, settlement, etc. and steep temperature variation being exposed, cause development of cracks in the roof slab and water start leaking from these cracks.

While constructing RCC roof slab, it should be borne in mind that the practice of using concrete which is not watertight and placing too much reliance on the waterproofing measures is not desirable. Concrete should be made watertight in itself and the waterproofing method should be looked upon as additional safety devices.

The grade of roof slab concrete shall be strictly as specified by the designer. The concrete materials should be properly proportioned, maintaining the specified maximum water, cement ratio, minimum cement content and required workability. The concrete should be admixed with a Superplasticiser.

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ROOF WATERPROOFING BY BRICK BAT COBA
Roof slabs constructed either by RC or RCC needs insulation for thermal comfort and waterproofing treatment to prevent leakage of water. Both these requirements are effectively full fill by brick bat coba treatment, the details of which are being below:

All existing treatment, coatings on roof slab top is to be removed and surface cleaned by hard wire brush and washed with water. The surface should be free from any oil, grease, dust etc. Remedial measured by provided to all structural cracks. Expansions joints should be treated as per standard practice.

All non-structural cracks more than 0.5 mm wide and construction joints if any, should be cut in “V” shape, cleaned with wire brush and washed, the cracks are then filled by polymer modified cement or mortar using acrylic polymer, with addition cement slurry mix is spread upon cleaned SSD roof surface. Over this 15 mm thick cement, sand mortar, 1:4 admixed, with water proofer is laid.

BRICK BAT LAYING
On the above green mortar, a layer of brick bats, soaked over night in water, is laid, having an average thickness of about 110 mm, about 70 mm near rain water pipe and 150 mm at ridge.

The gaps between the brick bats are generally kept between 15 and 20 mm. These gaps are filled with cement sand mortar, 1:4, admixed with waterproofer. In hot and dry weather, the surface should be covered with wet gunny bags immediately after finishing. Curing should start next day and continued for 7 days.

FINISHING LAYER
The top surface is then finished smooth with 20 mm thick cement sand mortar, 1:4, admixed with a waterproofer. All liquid admixtures should be mixed with the mixing water. The surface when green is marked with 300 mm false squares. Curing is to be done by ponding.

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REFERENCES
1. Kishore Kaushal, “Polymer Modified Mortars for Concrete Repair”. Civil Engineering & Construction Review, Nov. 1994, pp. 31-37.
2. Kishore Kaushal, “Polymer Adhesives Application in Concrete”, NBM & CW Dec. 98, pp. 21-26.
3. Kishore Kaushal, “Waterproofing of Buildings”, NBM & CR, Apr., 2000, pp. 50-55.
4. Kishore Kaushal, “Repair of cracks in Concrete Structures”, NBM & CW, Jul. 2000, pp. 65-68.
5. Kishore Kaushal, “Terrace & Roof Top Gardens”, NBM & CW Mar. 2001, pp. 68-72.
6. Kishore Kaushal, “Waterproofing of Old heritage Building with Ferrocement & Construction Chemicals”, NBM & CW May. 2001, pp. 54-57.
7. Kishore Kaushal, “Polymer Modified Mortars and Concrete Mix Design”, ICI Journal, Apr-Jun. 2001, pp. 39-42.
8. Kishore Kaushal, Dr. Krishan Kumar, “Waterproofing of Basements & Corrective Measures”, Proceeding of Seminar
on Structural Rehabilitation and Waterproofing. The Institution
of Engineers (India). All India Seminar 13-14 Oct. 2003,
pp. 19.1 – 19.5.
9. Kishore Kaushal, “Waterproofing of Basement”, CE % CR Dec. 2003, pp. 34-38.

We are thankful to Er. Kaushal Kishore for submitting this very useful research paper to us.

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Kanwarjot Singh

Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

44 comments on "Roof Waterproofing By Brick Bat Coba"

Basavaraj.S.Anadoor says:

i need the cement co efficant for the 1:1 avg 110 thk brick bat coba

Amrish Tyagi says:

for Brick bat coba in sunken portion is take CM(1:3) as 25% of total volume cement co efficiant for mortar is 9.6 bags/m3
For roof treatment it should be mortar 50% of total Volume

Sasikala says:

Any IS Code reference for brick bat coba

Pradosh says:

Sir,please give me the details of brick bat coba and the expense of doing the brick bat coba per SqM.

imran chowhan says:

brick bat coba is very effective on terrace, sunken area the total cost for brick bat coba is 725.00 per sqm.

Pilla Nageshwara Rao says:

Please send me the details about this way of water proofing

R.C.TARKAR says:

IS CODE FOR BRICK BAT COBA AS A ROOF TREATMENT WITH APPLYING METHODOLOGY.

dr supriya shukla says:

Pl send me the expenses of doing BBcoba per sqm and precautions for the technique ?

amit mishra says:

the expenses of waterproofing app.700=00rs persqm

Satya Veer Singh says:

Dear Sir, Cement provides strength but is not compatible to huge temperature fluctuations particularly in north India which results in cracks after a couple of seasons and water seeps through these cracks. Any effective and long lasting remedy for this?

Sanjay Agrawal says:

3-4MM APP MEMBRANE WATER PROOFING WITH LOWER WEIGHT FOR MINIMUM 10YRS

Rajan Puri says:

We have been using 8-8.5% micro silica and glass fibre in all our mix design whether M 35 or M 50 as a standard practise all though structure is Gr + 7 ( PT beams n slabs or Pt Beams n RCC slabs) . Would like to know if by mixing Polymers we could acheive better quality and life ?

m.k.sheriff says:

Sir, brick bat means brick on edge we can lay 110mm thick brick on edge how to lay for the thicknesses 70 mm and 150 mm please display with drawings becase most of the engrs think this is brick jelly cement concrete

shambhu dora says:

sir plz send me method statement of brick coba and sunken treatment.

Ajay says:

What is the approx. Area covered in 1 Brass Brick peices (Half Bricks )

jitendra says:

one bage .0019 aria coverd

r g gupta says:

1)what is the size of brick bats used for brick bat coba ?
2)if the size of brick bats are < 50 mm then ,how the gap is maintained as 15 mm to 20 mm

Purna Chandra Rao Sari says:

Dear Sir,

for temperature control for roof floors if we use lime instead of cement for brick bats jointing, is it useful or not? please give me your advise.

B.L verma says:

why brick is used in brick bat type waterproofing

Dk says:

coz brick has good water absorption capacity… it absorbs water and rarely let it pass through slab concrete.

Hiren Rathod says:

I like this Paper on Brick Bat Coba

JAGJIT SINGH says:

can any one help me about coba meaning

sures says:

please sir how many bags in cement for per sqm brick coba

ajay says:

how can we decide cement grade to compare wheather

sameer says:

pl.why use brick in this type of waterproofing? pl.send me methodology and name of chemical is used waterproofing in Indian market/company.

Aiswarya says:

Sir Please send me Cement adequasy for 1:2 in terrace water proofing using brickbat coba

Rajesh Rathava says:

Amrish Tyagi
for Brick bat coba in sunken portion is take CM(1:3) as 25% of total volume cement co efficiant for mortar is 9.6 bags/m3For roof treatment it should be mortar 50% of total Volume

What may be the consuption of cement under praportion of 1:3 for roof Water proofing in Brick bat coba per Cmt. of BBC?

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