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Waterproofing for Internal Wet Areas – Preparation Works


The Waterproofing Specialist must have his shop drawings approved for construction by the Designer.

A meeting should be called in the early stages of construction by the Contractor to ensure that all involved parties understand the sequence of work. In planning the sequence of work, adequate time should be allowed for the waterproofing membrane to cure and dry.

The requirements that must be satisfied at each stage or phase of the process should be stated in an inspection and test plan (ITP) prepared by the Contractor. An example of an ITP is given in Appendix D. The checks required by the ITP can be specified in a checklist that should be used to record the results during the verification

The Contractor must ensure that all pipe, duct and any other works that penetrate the floor slabs and walls should be completed before the start of waterproofing work. M&E clearance for the plumbing and sanitary fittings at wet areas should be obtained prior to concealing them. The pipes should be pressure and flow tested and free of leakage. To ensure that all involved parties understand their requirements, the Waterproofing Specialist should complete a “mock-up” to demonstrate the substrate requirements and preparation, and all other works that must be completed by other trades before application of the waterproofing system. Safety requirements, method of installation, watertightness tests and protection of membrane must also be demonstrated.


Proper preparation of the concrete surface is an important factor in ensuring good performance of the waterproofing system. The area to be waterproofed should be prepared according to manufacturer’s recommendations prior to the application of the waterproofing system. For instance, blistering will occur if certain non-breathing materials are applied to wet substrates.

Concrete surfaces shall be cleaned and free from all forms of scale, laitance, dust, mould, form oils, wax, curing agents as well as any other foreign materials that may cause debonding of the waterproofing membrane from the substrate.

Generally, two methods of cleaning may be employed: mechanical cleaning and chemical cleaning. Mechanical cleaning methods (i.e. compressed air, industrial vacuum cleaning, sweeping, abrasive cleaning, high-pressure water jetting and grinding) are effective in removing laitance, dust, efflorescence, loose plaster and weak surface materials. Chemical cleaning methods are effective in removing oil, grease and dirt. Efflorescence or leached salts should be removed from masonry surfaces with approved cleaning agents, according to the masonry surface type.

A continuous angle fillet (25 x 25 mm) should be installed at all internal corners between horizontal and vertical surfaces. The fillet material is usually 1:3 cement sand with 1:4 bonding agent and water. The fillet serves to make the joints more gradual for the membrane to sit on. Alternatively, reinforcement (for eg, fiberglass mat) of 150mm width can be installed at the corners. Please see Chapter 6 for the actual application of the reinforcement.

For brickwalls, the mortar joints should be flush pointed and rendered with cement/ sand mix to receive membrane (see Fig 5.4). Ensure that rendering at shower areas, long baths and areas around wall hung basins, water cisterns, etc are applied to the required heights.

The following are pointers for repair of surface defects:

  1. Defective concrete substrate surface should be removed with tools that will not further damage adjacent areas.
  2. The repair material should be compatible with the concrete substrate being repaired. If dry pack portland cement mortar is used, the water/ cement ratio must be kept as low as possible to reduce
  3. A bonding agent shall be applied on the concrete to have better adhesion to the repair material.

Wet curing during the first 24 hours is strongly recommended. (Due to the relatively small volume of dry pack repairs and the tendency of the existing concrete to absorb moisture from new material, water curing is a highly desirable procedure, at least during the first 24 hours). Spraying of curing compound is not recommended unless the curing compound is compatible with the waterproofing membrane.


For certain types of membranes where a dry surface is required, good ventilation should be provided to enable the substrate to dry sufficiently. A moisture meter test should be carried out by the applicator to check the dryness of the substrate before membrane application. The meter should be correctly calibrated to the substrate type before use.

On the other hand, cementitious membrane systems require a damp surface to improve the adhesion of the membrane to the concrete surface. For application of such systems, remove all lying water from the concrete surface, then pre-saturate or dampen the substrate with clean water prior to application of the first coat of the waterproofing membrane.


To reduce the risk of water leakage at floor penetrations:

  • ensure that the portion of the pipe in the slab does not have joints.
  • create a slight upward sloping profile surrounding pipe protrusions (fillet for membrane upturn) (see Fig 5.6). Alternatively, reinforcement could be installed.
  • provide additional protection at these areas. The waterproofing membrane used to treat the pipes should adhere and be compatible with the pipe material and the subsequent membrane applied on to it. For water outlets, ensure pipes are cast to flush with floor level to facilitate membrane dress down.


Primers are usually applied to the substrate before the application of the actual waterproofing material, to enhance adhesion properties of the waterproofing system, eg, polyurethane system. Ensure that the concrete substrate is sufficiently cured before applying a recommended vapour barrier as a primer to the substrate. Primer should always be brush applied. Check the procedures as some membranes must be laid onto wet primer. The primer should also be applied to the render coat on the brick wall, ensuring full coverage and allowed to dry, prior to application of membrane.


Insufficient surface preparation at the concrete surfaces receiving the membrane material can cause debonding of membrane near the joints. Prior to the application of the joint sealant, all loose materials, debris and weak concrete that may inhibit the sealant from adhering to the joints have to be removed. Backer rods of appropriate sizes should be inserted into the joint as backing for the sealant material. The sides of the joint are taped before gunning the sealant into the joint. The joint is then tooled to achieve a smooth even surface, and the masking tape removed to allow the sealant to cure.

Source from BCA Singapore