How to repair concrete roof from bottom

 A terrace is nothing less than the extension of pure living space.
 Its a place to relax with family and meet people on a get-together,
 till it is decently maintained.

Before understand the repair procedure, you need to understand 
the typical cross-section of Terrace Waterproofing:

1.Structural Concrete (Roof Concrete)
2.Waterproof Coat (Elastomeric Polymer)
3.Protective Screed (12.5 mm thick)
4.Brickbat Coba (in Slope 75-125 mm)
5.Finishing Screed (20-25mm)

1. The waterproofing of the RCC slab has failed (Or)
2. No waterproofing has been done for the slab area

Step-1: 
Identify The Type Of Defect And Rectify Accordingly
Defect Type 1: Screed Debonding
Defect Type-2: Superficial Cracks On Screed
x
If there are leakages and visible cracks on roof, the one of the following can be inferred
The following checks the following before repairing the visible cracks (< 3mm) and
 do needful as guided
Check soundness of top screed, look for di-bonding signs by knocking it with fingers
. If you hear a hollow sound, then you need to remove the entire patch
 (making hollow sound) and repair it with a repair mortar (polymer modified mortar)
Visible cracks not giving hollow sounds need to be directly treated. 
Creating a “V” groove (10 X 10 mm) on the crack observed and clean
 the groove (with vacuum cleaner and/or water jet). Seal the frove with a 
Non-shrink repair mortar available with construction chemical companies 
like Permaindia, Sika, Dr.Fixit etc.


Step-2:
 Test The Adequacy Of Waterproofing Done
After doing above (1 & 2) fill the slab with water to a depth of 1-2”
 (usually known as water ponding) and check for damp signs (after 72 hrs.).
If there are no signs of dampness observed underneath the slab,
 then you are through with its repair.
If dampness is observed, you need to do waterproofing on entire slab area.


 Step-3:
You can also avoid the painful process of waterproofing by adopting
 an alternate treatment.
After sealing the cracks, clean the entire top screed surface thoroughly
 (remove dirt and deposits. They might de-bond the water proofing
 layer applied over the existing layer). Apply priming coat on the cleaned surface.
 Apply two coats of an elastomeric 
waterproofing chemical (having Ultra Violet ray resistance properties)
 on the top of priming coat. The construction chemicals are available with
 construction chemical companies like Permaindia, Sika, Dr.Fixit etc.
To check its waterproofing adequacy, do water ponding on slab and check
 for damp signs (after 72 hrs.).