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)