Hong Kong Housing AuthorityDMO/TWS Study Report for body-shop works supervisor II22 August 2014

1 IntroductionWater seepage is one of the most common defect found in high raise residential building, it will not only cause damage to occupants property, it may cause sanitary nuisance to the adjacent units. Moreover, excessive water could damage to the building substrate, causing defects like spalling concrete, such defects are possible to endanger the public safety and shorten the life expectancy of the buildingOwner of building have the responsibility to carry out the necessary investigation and repair work to resolve any seepage problem to ensure a safe & hygiene environment for the occupant.2 Possibly causes of water seepageThere is various causes of water seepage found in the reinforced concrete building, but in most cases, water seepage was caused by the following reasons:-

2.1 Leakage in the drainage pipes of the upper, adjacent or your own flat.2.2 Cracks developed on the partition wall, causing damage of the water proofing system

2.3 Deterioration of the water proofing membrane

2.4 Seepage of waste water/ rain water through roof/external wall2.5 Non-standard tenant fixture/modificationPhotos:

Description:2.1 Defective drainage pipe was noted, water seepage causing peeling off of paint and rusting on the pipe.

Description:2.3 Water seepage caused by non-standard socket installed by tenant on the dry wall of toilet. Thus, waterproofing membrane on the toilet wall was damaged.

3 Repair method of water seepageFor the repair of water seepage in individual units in public housing estate, 2 methods are commonly used:

Tanking method

Resin injection method

In vacant flat refurbishment, tanking method will be used to repair the seepage problem in service area. Item 270210(For floor and skirting of toilet), 270230(For floor and skirting of balcony and kitchen) & 270240(For wall of one toilet) will be issued to tackle the water seepage problem.

4 Water seepage repair by Tanking method in vacant flat4.1 Material

The proprietary water-proofing material used in Choi Wan (I) Estate vacant flat is Masterseal 540 supplied by BASF. It is a water-proof coating designed to be used as an effective water-proofing membrane.Masterseal 540 is a two part, pre-packed system, consisting:-

Part A liquid polymer (in 5kg or 10kg packing) Part B pre-mixed powder (in 13kg or 26kg packing)4.2 MixingThe mixing ratio of Masterseal 540 should be 10kg part A with 26kg part B.

75% of liquid polymer should be add into a clean pail first. Then add the Part B into the pail slowly with the mixer running. Mix for at least 3 minutes to get a lump-free homogeneous mix. Add the remaining 25% of Part A to get the required consistency.4.3 ApplicationThe application of Masterseal 540 should be using a paint brush to apply at least 2 layers to achieve an effective tanking. The first layer should be dried before the application of the second layer.

4.4 Storage

As recommended by the manufacturer use of part packs should be avoided.Photos:

Description:Masterseal 540 Part A & Part B

Description:Heavy duty electric drill with wing type paddle

5 Critical stages of Water seepage repair in vacant flatThere are two critical stages of during water seepage repair:-5.1 Take down of existing tiles

Existing wall and floor tile including tile adhesive and cement send backing should be taken down before the application of water proofing material.

Any cracks and holes should be filled up with cement send to provide a flush surface to ensure the water proofing layer thoroughly applied on the floor and skirting.Any new door frames or thresholds should be installed at this stage to ensure the integrity of the water proofing layer.

The prepared surface should have adequate bonding for plastering without loose material. Further checks with void detector for any hollowed section are recommended.Water proofing material should be delivered on site at this stage. Marking of site location and date are required to make sure the material can only be used at the subject location

Angle fillet should be applied before the application of water proofing materialPhotos:

Description:Existing tiles and tile adhesive were hacked off

Description:Void and cracks were filled up before applying waterproofing material.

Photos:

Description:New door frame and threshold were in-place

Description:New pack of Masterseal 540 was marked with date and site location

Photos:

Description:Angle fillet was applied before the application of tanking material.

5.2 Water tightness testAfter the tanking is completed, a water tightness test is required to carry out to make sure the new water proofing membrane is effective. The procedures of water tightness test are listed as follow:- Fill up the tanking with water of 50mm depth for at least 8 hours

Check the used package of the water proofing mater to make sure the material was used on site

Check the coverage of the water proofing layer, normally the water proofing membrane will cover not less than 300mm height at skirting above finished floor level. For shower area, it will not less than 1800mm height above finished floor level.

Check the workmanship of the water proofing layer to eliminate any bubble/cracks/trowel marks on the surface. Check the adjoining area at living area for any sign of leakage For the shower area, use domestic type hand held shower head with water pressure 20-30 bars to conduct the water tightness test against the wall surface for 4 minutes. After the water tightness test is completed, check the adjoining area again and the ceiling of the flat below the subject flat to make sure there is no leakage at the new tanking.Photos:

Description:Used package of Masterseal 540

Description:Check for the workmanship and coverage of the tanking

Photos:

Description:Tanking area was filled by 50mm depth water for at least 8 hours.

Description:Adjoining area at living area was checked and no seepage was noted.

Photos:

Description:Conduct water tightness test with domestic type shower head

Description:Water pressure: 30-35 psi

Photos:

Description:Try to gain access to the unit below for further checking

Description:Check the ceiling of the unit below.

6 Water seepage repair by Tanking method in occupied flatThe situation of repairing in occupied flat is different from vacant flat because the whole process should be completed within one day. Therefore, fast-set cementitious waterproofing material was used in occupied flat.6.1 Definition of fast-setScreeding or coating has an initial set time of about 30 minutes and enables foot traffic in one hour.

6.2 Material

The proprietary water-proofing material used in Choi Wan (I) Estate occupied flat is Monoset RXG supplied by Ronacrete. It is a water-proof coating designed to be used as an effective water-proofing membrane.

Masterseal 540 is a two part, pre-packed system, consisting:-

Part A liquid polymer (in 5kg or 10kg packing)

Part B pre-mixed powder (in 13kg or 26kg packing)6.3 Critical stages

Similar to the method used in vacant flat, there are two critical stages.

6.3.1 Take down existing tiles

Same as section 5.1

6.3.2 Water-tightness test

Water should be sprayed to the walls at a height of 300 mm above finished floor level or at the top junction between the existing wall finishes and over the entire floor, floor drain and bottom edge of shower tray for 4 minutes. Immediately inspect the floor to check whether ponding exists and the required falls have been provided and the opposite side of the wall where waterproofing system applied.

After 30 minutes of the water spray, inspect one floor below to check seepage at pipe sleeves, at the trap at the soffit. If access to the flat below cannot be gained, the Contractor shall leave a feedback sheet at the entrance door and request the PAGE PAGE 16Prepared by LEUNG Ho-yin (WS2/TWS12)