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Waterproofing Your Bathroom

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Bathrooms these days are not just meant for freshening up, but are more visualized as personal spaces to get refreshed and also rejuvenated. However, frequently exposure to water moisture and constant damp conditions spoil the overall attraction of the bathroom. Tirthapratim Banerjee, Head – Training, Pidilite Industries Limited explains the reasons of water leakage and tries to acquaint us with impacts of prolonged water movement and provide knowledge on the best-in-class solution or treatment to stop such water penetration.

Wet areas occupy less than 10% of the gross floor area of an apartment and the annual maintenance cost can range from 35% to 50% of the total maintenance cost depending on the type of facility. However maintenance costs go up substantially when remodeling or repairing bathrooms which are frequently exposed to water moisture and subjected to constant damp conditions with alternating drying and wetting cycles.

Possible points where leakages take place

  • Drainage line openings through the walls & floor (pipes & nahani trap)
  • Concealed water lines – buried PVC / GI fittings & pipe joints
  • Wall & floor tile joints (improper tile grouting)
  • Water lashed walls near the shower area
  • Bathroom door jambs & threshold fitting
  • Joints adjacent to shower tray/bathtub/wash basin etc.

Leakages in bathrooms are mainly due to lack of knowledge about bathroom waterproofing techniques and the right choice of products. Additionally lack of proper slope of floor areas for draining water through the outlet points adds to leakages.

Such leakages cause dampness on walls adjacent to bathroom and dirt and algae accumulate in tile joints filled with white cement. Persistent dampness in the house is conducive to fungal growth and harmful to residents and also cause nuisance to the residents at floor below in multi-storey buildings. Repairing and refurbishment involves 15-20 days of messy work and incurs high costs.

Traditionally bathroom waterproofing follows the conventional structure of first fixing the plumbing lines including the concealed intake and outlet pipes, next laying a screed on the concrete slab with polymer waterproofing coating and laying of brickbat coba, then leveling & plastering of walls, laying tiles on the floor and wall areas and finally installing fixtures and sanitary ware.

Waterproofing the bathrooms with conventional practices as mentioned above have certain limitations – the PVC pipe inserts do not adhere well with the brickbat coba / cement / concrete used for filling the areas and joints around the pipes. The polymer waterproof coatings and the brickbat coba have limited ability to withstand cracks and insufficient attention to detail is paid in the corners and joint areas of the bathrooms.

How to secure all these possible leakage points

Bathroom waterproofing needs a very systematic approach with detailed specifications for all the sections including floors, walls, splash zones, plumbing lines and tiling. A generic outline as per internationally approved Australian Standard of “Waterproofing of Wet Areas” is mentioned below.

Adequate drop is to be provided during casting of floor slab to ensure that the finished level of the wet area is sufficiently lower than the level of adjacent concrete slab to prevent migration of water into the dry area. If pipes are encased in screed, a minimum 20mm thick screed is to be provided at the floor water outlet level – accordingly the drop in floor level should be adjusted.

WP membrane should extend 150mm from the wet area into the concrete slab of adjoining dry area. Alternatively, monolithically casted concrete kerbs may be used to prevent moisture migration into the dry area.

Joints at walls – brick wall and RCC columns, are to be minimized. Separation gaps, if provided should be filled with proper Polymer modified mortar (PMM) with mesh reinforcement.

Walls are to be rendered to a minimum height of 300mm from floor level for a smooth finish to receive the WP membrane upturn. Similar rendering up to specified height and width of the walls at shower and bath areas is to be considered. Rendering should incorporate an integral waterproofing compound ensuring its water tightness.

Kerbs of minimum height 100mm is to be constructed at the base of the walls to act as barriers to lateral movement of water.

For wet areas with high amount of water splash, the WP membrane should turn up to a minimum height 300mm to ensure a complete tanking protection against water migration to adjacent spaces and below the wet areas.

The membrane should extend minimum 100mm horizontally from the wall-floor joint to create sufficient lapping with the subsequent membrane application.

Corner fillets to be provided beneath the WP membrane. If corner fillet is not provided, the mesh reinforcements like fiberglass can be incorporated.

A water tightness test should be carried out with a flood of water of 25mm height upto 24 hours to ensure the effectiveness of the WP applications at the base floor and adjacent wall levels. At bath and shower areas, the WP membrane should be applied to at least 1800mm (around 6ft) height and 1500mm (around 5ft) width of the wall or the entire width of the enclosure for a better protection.

The wall or substrate immediately adjacent or behind a basin, sink or similar fixtures must be applied with WP membrane to a height not less than 300mm above the fixture, if it is within 75mm of the wall.

The joints between the fixtures and the wall are to be filled up with elastomeric sealants to ensure no gap is provided for passage of water. Normal white cement should not be used for such purpose as it may lead to crack development in joint-filled areas.

Concealed plumbing in the walls require special protection for any unwanted leakage. The area around the pipes should be filled with impermeable polymer modified mortars so that any water percolation will not directly come in contact with adjoining walls.

Apply a polymer bond coat before the mortars placed in position to avoid any surface leakage.

An adhesive tape should be wrapped around bathroom pipes (both horizontal and vertical) blocking leakages around nahani trap and pipe joints.

A top screed should be laid to slope towards the floor outlet and indicated in the design itself keeping in mind with pedestrian traffic flow.

Tiles or any other barrier surface may then be laid on the screed with proper tile bonding adhesive compatible to the WP screed.

Similarly before applying tiles to wall upturns and shower areas, a minimum 20mm thick layer of plaster should be provided over the WP membrane.

The joints between tiles should be filled with proper impermeable polymer based tile joint filling materials.

Selection of Suitable Waterproofing Materials

The selection of waterproofing materials should be based on life-time cost performance – including the cost during initial construction and the cost of renovation with replacing the old systems and providing a new WP layer.

Though there are several materials available in the market, one should understand the following basic properties of the materials before selecting the right choice – it should be able to bridge over cold joints and withstand minor cracks. It should be compatible and easy to apply, especially at pipe penetration areas. It should be elastic enough to bridge over differing materials and have good adhesion and cohesion strengths. It should be able to receive screeding and plastering. Should be resistant to any mechanical damage prior to screed finish and bonded to the substrates to isolate any leaks in future

Water tightness of bathrooms relies mainly on the adequacy of waterproofing over penetrations, projections and joints and how these discontinuities of the floor and wall elements can achieve a “monolithic” structure. Moreover, to make “leak-free” bathrooms and toilets, the decision to select a specific waterproofing system should take into consideration of the substrate and area of coverage for a cost effective solution.

Bathroom being the main wet area in anybody’s dwelling space, the correct approach to its water tightness not only reduces the risk of damage of your house but also makes the living more comfortable and healthy in a long run.

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