UNIT VI---UNUSUAL PROBLEMS bc 5th sem breif notes

UNIT VI---UNUSUAL PROBLEMS

 

Water Proofing The Roof Terrace: 

Recommendation 

 The old cover concrete and system should be examined for its soundness.
  The slopes shall be checked for its effective drainage of rain water. 
 The surface cracks shall be fixed with polymer modified cementitious crack filling compound. 
 Injection pressure grouting is carried to fill the voids in the concrete by drilling holes at regular intervals c/c 1mtr by admixing Grout additive and integral water proofing admixture. 

Line of Action 

 Dismantle the old system 
 Surface preparation 
 Fill up all the cracks 
 Injection pressure grouting 
 Fixing down take pipes 
 Fixing joint tape 
 Membrane coating 
 Final layer of cement mortar screed 
 Coving 

Specification for terrace waterproofing 

For new constructions: 

To obtain a sound waterproofing layer please follow the following procedure- 

 Clean the surface of all loose particles, dust, cement laitance etc.  
 In case the slab is uneven and undulated it is desirable to make it level and smooth using a thin cement sand mortar.  
 Moisten the R C slab (or the leveling mortar) 
 Apply slurry of Polymer based chemicals and Cement.The slurry should be freshly prepared, uniform in consistency and suitable for brushing 
 Apply 2 more coats at 24 hour intervals each, when the already applied coat would have set & hardened.  
 Allow setting for 48 hours.  
 Cure the coating with wet squeezed gunny bags.  
 Finish the surface as per requirement. 


For existing terraces: 

Generally the leakages may be on-  

 account of the failure of the IPS or China Mosaic,  
 the cracking and failure of the insulation layer,  
 the failure of both.  
 Defects or distress in the R.C.C. slab. 

For case (a) follow the steps given below - 

 Remove the finishing layer of IPS or China Mosaic totally to expose the insulation layer.  
 Clean the insulation layer  
 Provide a 1:3 cement-sand leveling and smoothening course less than 10 mm thick. 
 After the layer in has hardened say 24 to 48 hours, on the wetted surface, apply Polymer based chemicals and Cement slurry in the ratio 1:1.5 by weight 
 Apply 2 more coats at 24 hour intervals each, when the already applied coat would have set & hardened.  
 Cure with damp gunny bags.  
 Finish as required. 

For case (b) & (c) follow steps given below - 

 Remove the finish layer & insulation layer, to expose the structural reinforced concrete slab. 
 Clean the slab and inspect for cracks and defects.  
 Seal cracks if any with Polymer rich cement mortar   
 Level and smoothen the surface with 1:3 cement mortar about 10-15 mm thick.  

For case (d) follow the steps given below-  

 Identify and mark out the defects – i.e., cracks, honeycombing etc. 
 Repair the cracks with Polymer Rich Cement Mortar. 
 Grout the honeycomb areas with Polymer Cement Grout 

Leaks from overhead tanks: 

 Overhead tanks are potential sources of leaks where proper waterproofing has not been done. The wate from these tanks can enter the slab,beams,columns or brickwork of the total building and damage the structure as a whole. 

 It is always advisable to have R.C.C tanks and not overhead tanks made of brickwork as brickwork tanks crack and deteriorate easily. 

Precautions:- 

Proper waterproofing on the internal walls of the tank should be done after sealing all the gaps between pipelines. 

Leaks through cracks: 
 Cracks in internal and external walls occur due to various reasons and it can also be a source of water ingress into buildings. 

Precautions:- 

 All cracks upto 5mm shall be cut open and filled with acrylic paintable sealant  If large cracks are formed, resources like micropiles are available to prevent future occurrence of these cracks. 

Leaks through fungal formation: 

 Ingress of water into the buildings leads to dampness in the walls leading to fungal growth causing staining and discolouration. 

Precautions:- 

 The source of leakage has to be arrested 
 An internal anti-fungal acrylic based crack bridging wall coating has to be applied. 

Leaks through concealed pipelines: 

 Leakage of water can take place due to failure of concealed pipeline joints. Such leaks can be identified as dampness. 
 Leakage from toilets due to failures of waterproofing of the sunken slab also takes place. 

WATER LOGGING: 

Water logging around the buildings and increase in ground water table can lead to water comingup through the flooring sometimes. 

Prevention: 

To prevent water logging, the level of building has to be raised above the road level and sloped towards the road or the external drain.