Waterproofing for Internal Wet Areas – Material Selection
Following the design of the wet area by the Designer, the Contractor will propose a suitable waterproofing system. Selection should be based on life-time cost-performance. This should include not only the initial performance and cost of the waterproofing system, but also the cost of replacing a waterproofing system failing prematurely and other costs associated with failure.
An experienced and qualified person should review the qualities of a recommended product in meeting existing standard test or specifications. The selected system should be reviewed and agreed with the Designer. Test certificates of the product should be submitted to confirm their compliance with the stated specifications.
WATERPROOFING SYSTEMS FOR INTERNAL WET AREAS
Waterproofing systems can be generally classified into 3 main categories, namely preformed membrane, liquid applied membrane and integral systems. An overview of the general waterproofing systems is given in Appendix A.
Preformed membrane systems are suitable for large areas with minimum protrusions. In Singapore, they are not commonly used in the internal wet areas.
Integral systems, such as the concrete admixture system and the crystalline system, are waterproofing systems that become part of the reinforced concrete structure that they are protecting. However, these systems cannot withstand movement and the waterproofing capability will be severely undermined once concrete cracks develop after the waterproofing application.
Liquid applied systems are normally preferred over preformed systems and integral systems for internal wet areas because of the following advantages:
- Continuity of the membrane between horizontal and vertical planes, around projections and penetrations and it is self-flashing.
- Membrane adheres to every part of the substrate, which helps in isolating leaks and preventing lateral movement of water.
- Membrane is able to withstand minor cracks.
However, liquid applied systems require more supervision and quality control during substrate preparation, mixing (some coatings require mixing on-site) and application. Weather conditions such as ambient temperature, precipitation, and humidity can affect the quality of the application. Certain liquid applied products, such as the polyurethane and rubber systems, have two formulations (one for horizontal and one for vertical application) which must be ascertained before application. Curing requirements for acrylic based liquid applied waterproofing system must be followed strictly or it may not be suitable for usage under constant immersion or with an active hydrostatic head of water.
Liquid applied systems can be classified into water based or solvent based, depending on whether water or solvent is used to create a liquid form. Consult the manufacturer for the classification of the product used.
Solvent based systems
Most solvent based systems will have slightly better adhesion especially if they are epoxy or urethane based. However, solvent based membrane demands st
ringent surface preparation before application. Normally, the surface has to be totally dry and free of dust to ensure good bonding. Certain solvent based systems may affect PVC, other plastics or some metal fittings. Check with manufacturers and obtain their confirmation if in doubt.
Water based systems generally adhere well to moist substrate but may blister if substrate contains excessive moisture. It is a good practice to ensure the substrate is relatively dry. Use a moisture meter to check the relative dampness before application. Some water based system may require special primer, especially for application on metallic finishes. For water based cementitious systems, the membrane could be adversely affected, under a process called hydrolysis, if water test is conducted before the membrane is fully cured and set.
Performance of screed is important especially for wet areas and depends on the mix proportions and method of mixing. If control of such factors is poor, the screed will have shrinkage cracks which may become potential paths of water seepage. This will result in faster deterioration of the waterproofing membrane beneath it and as a result, the life span of the total waterproofing system in wet areas will be shortened.
For wet areas, the waterproofing screed could be specified as a secondary layer of defense. The waterproofing screed may be prepared by gauging cement mortar with a waterproofing compound to reduce its permeability. For specifications on waterproofing screed, refer to CP 82:1999. Waterproofing screed can also be specified for internal areas where intermittent wetting is expected. A minimum 20mm screed thickness is normally adequate to provide the watertightness.
For better site control of the mix quality, pre-packed waterproofing screeds, which are dry mixed and packed with the waterproofing additive in the factory, are recommended. Workers need only to add the correct amount of water to the pre-packed mix on site using a mechanical mixer to produce the desired mix.
The waterproofing system for wet areas should:
- be able to bridge over cold joints
- be compatible and easy to apply, especially at pipe penetration areas
- be elastic to bridge over differing materials
- have good adhesion and cohesion strengths
- be able to receive screeding and plastering
- to a certain extent, be resistant to some mechanical damage prior to screed finish
- be fully bonded to the substrates to isolate any leaks in future
It is important to note that two products of the same generic type may vary extensively from each other depending on their chemical composition. For this reason the fundamental properties/characteristics of the different products (given by the manufacturer) must be checked against those specified by the designer. Table 3.2 gives the performance standard specifications that could be referred to as a guide for specifying liquid applied waterproofing systems in wet areas.