The purpose of the application of waterproofing is to prevent the water to percolate or penetrate into any underground concrete members. When the water penetrates into the sub-grade concrete-like foundation such as mat foundation, footing, tie beam, etc. the steel reinforcement that embedded in the concrete would corrode due to a chemical reaction caused by water and the structure would eventually fail.
Application of waterproofing especially for large structures would have to be strictly supervised by a quality engineer in order to prevent failure of application or nonconformity to the quality procedure.
In this method statement, we’ll be going to use the membrane type waterproofing, this type of waterproofing is advisable for structures like high-rise buildings which has a deeper foundation where water pressure is extremely high.
Here is the method statement for application of waterproofing membrane.
Method Statement for Application of Waterproofing Membrane
2. Purpose and scope
The purpose of this method statement is to describe the measures and ways of the proper application of waterproofing membrane in our project. Work shall be carried out as per the drawing and project specification.
3. Work procedure
- Work preparation and application of primer:
- Any undulations or protrusions on the surface would be removed in order to obtain a smooth surface. The surface must be thoroughly cleaned and free from dust, dirt loose materials, oil or grease.
- 50x50mm size fillet made of cement-sand (1:3) mix would be placed along corners of walls or neck columns and any other junctions.
- For horizontal waterproofing membrane application. Two layers of 4mm thick modified bituminous membrane shall be laid fully torched on blinding concrete with a minimum of 100m end laps and 150mm side laps.
- The blinding surface shall be primed with the primer recommended by the manufacturer of the membrane prior to placing the membrane. Prior to succeeding works, the applied primer shall be inspected by the Engineer 24 hours after the placement.
- Waterproofing membrane installation shall be performed using cylinder fed propane gas torch, trowel to seal the seams of the membrane and knife for cutting.
- The membrane is then placed in the correct torching on position then re-rolled for about half of its length without changing its orientation.
- The membrane is then un-rolled again and torched on pressing the melted area against the substrate.
- Repeat till the entire length of the membrane is bonded firmly onto the surface then the second membrane is laid in the same way with an overlap of 150mm at the end and 100mm at the side.
- An extra length of minimum 300mm of the horizontal membrane shall be left to carry up the vertical surface to maintain continuity of the membrane and be protected as above.
- For vertical application, two layers of 4mm thick modified bituminous waterproofing membrane shall be applied to all vertical surfaces of gunited shoring or blockworks wall.
- Before applying the waterproofing membrane, concrete surfaces shall be primed with primer recommended by the manufacturer of the membrane but then again it should be inspected by the Engineer 24 hours after the placement.
- The extra portion of 300 mm of the horizontal membrane left shall be turned up and wrapped on to the vertical primed surfaces. The continuity of the membrane shall be maintained by minimum laps of 150mm.
- The membrane on the exposed external vertical surfaces shall be carried up to a minimum of 150 mm above the finished ground level (i.e. sidewalk, parapet, etc.) and tucked into a continuous groove provided for the same and secured firmly with approved sealant/mastic recommended by the manufacturer of the membrane.
- The membrane fixed on the gunited or concrete wall shall be protected from any damage due to rebar fixing, formworks, concreting of the raft, retaining wall works with approved type protection board fixed to the membrane.
- All areas of the membrane exposed above ground shall be protected with appropriate flashing.
- Inspection would be submitted for approval of the Engineer.
- Before fixing of steel reinforcement for foundation, the membrane shall be covered by one layer of polythene sheet and poured with 50 mm thick layer of cement-sand screed.
- All works shall comply with safety procedure or instruction as set out in project safety plan and municipality rules and regulations. All safety recommendations as advised by the approved sub-contractor.
- Basic PPE to be worn by all staff or laborers.
- Provide lighting when working at night.
5. Equipment and tools
- Bobcat or JCB
- Wheel borrow
- Metal tape
6. Materials and references
- Modified Bitumen Membrane
- Specification Section – Waterproofing
If you have any suggestions and comments on the above method statement please feel free to leave your reply below.