A large share of water damage in buildings starts not at the roof or the foundations, but in the interior spaces that are in contact with water every day. In bathrooms, kitchens, WCs, laundry rooms and balconies, ceramic tiling and grout do not make a surface watertight on their own; water seeping through joints and through detail points such as floor drains and pipe penetrations gradually works its way into the screed and the concrete slab. The usual outcome is staining on the ceiling of the flat below, blistered plaster, mould growth and leak disputes with neighbours. Bathroom and wet area waterproofing is the engineering solution that stops these problems at their source by forming a continuous, flexible waterproof layer beneath the tiling.
Waterproofing a wet area means combining the right material with the right detailing. The drain surround, the wall-floor junction, pipe penetrations and the shower zone are the critical details that decide whether the application succeeds; most leaks start at these points, not across the open surface. Under-tile waterproofing is therefore not simply a matter of brushing on a product — it is a process that must follow the specification from surface preparation and detail tapes through to coat thicknesses and curing times.
EREL Yalıtım, built on its founding team's more than 20 years of industry experience, works in waterproofing with its in-house engineering team. Across Istanbul we deliver projects of every scale on a turnkey basis, from individual apartment bathrooms to the communal wet areas of hotels, dormitories and shopping centres. We inspect the substrate and usage conditions on site, select the right system from the global ranges of our solution partners, and complete the application in accordance with the technical specification.
Where Is Wet Area Waterproofing Needed?
A wet area is any space in a building where water is used continuously or periodically. The bathroom is the best-known example, but the scope is much wider: kitchen floors and worktop zones, WC and washbasin areas, laundry and boiler rooms, balconies, communal shower blocks in hotels and dormitories, changing and shower rooms in sports facilities, and the surrounds of spas, saunas and pools all belong to this group. Bathroom waterproofing is the most frequently requested of these applications, because in the shower zone water reaches the surface directly and under pressure, the space is used daily, and even the smallest detailing error shows up in the flat below within a short time.
In new construction, wet area waterproofing is a standard work item that must be completed before the screed and tiling. In existing buildings it usually comes onto the agenda only after a problem appears: yellowing on the ceiling of the flat below, blistering paint in the room adjacent to the bathroom wall and damp marks along the skirting line are the typical symptoms. In that case the tiling has to be removed, the source identified and the waterproofing rebuilt. At EREL Yalıtım we pay particular attention during the site survey to identifying the true source of the leak, because a plumbing leak and missing waterproofing call for different remedies — and a wrong diagnosis means paying twice.
- Bathroom, shower and WC floors and walls
- Kitchen floors and splash zones in front of worktops
- Balconies and enclosed terrace-type areas
- Laundry rooms, boiler rooms and technical spaces
- Communal wet areas in hotels, dormitories, hospitals and sports facilities
- Spa, sauna, steam room and pool surrounds
Under-Tile Waterproofing Systems and Material Options
The most common and reliable method in wet areas is under-tile waterproofing: the waterproof layer is applied over the screed and the ceramic tiling is fixed directly on top. The principal material group used for this purpose is cementitious two-component flexible slurry membranes. Mixed on site from a powder and a liquid component, these products bond fully to the substrate, tolerate hairline movement in the screed thanks to their crack-bridging capability, and leave a surface ready to receive tile adhesive. We select systems from this group from our solution partners' global range according to the requirements of the project.
The second group is ready-to-use dispersion-based liquid membranes. Applied by brush or roller with no mixing required, they are a practical option for small and medium-sized jobs such as residential bathrooms. For zones under permanent water load, such as shower bases, cementitious or polyurethane systems are preferred. Whichever material is chosen, detailing decides the outcome: without flexible sealing tapes at wall-floor junctions and corners, pipe collars at penetrations and the correct components around the drain, the application will leak no matter how good the membrane is.
Material selection weighs the intensity of use, the duration of the water load, the substrate type and the finish to be installed. A bathroom with underfloor heating, for example, needs a flexible system that withstands thermal movement, while in permanently humid spaces such as steam rooms vapour diffusion must also be taken into account. EREL Yalıtım makes this assessment during the survey and states clearly in the quotation which system is proposed and why.
- Cementitious two-component flexible slurry membranes: the standard under-tile solution
- Ready-to-use dispersion-based liquid membranes: practical for small and medium-sized jobs
- Polyurethane liquid membranes: for details demanding high elasticity and continuity
- Flexible sealing tapes, internal and external corner pieces and pipe collars: the components that complete the system
- Primers and surface preparation products: the guarantee of adhesion performance
Interior Waterproofing for Damp and Moisture Problems
Not every water problem is solved by removing the tiling; in some situations the surface the water comes from cannot be reached from outside. Ground moisture entering through the retaining wall of a basement bathroom, water seeping in from a neighbouring plot in terraced construction, or standing water at the bottom of a lift pit are typical examples. This is where interior waterproofing comes in: the water is stopped on the inner face, from the negative side. Crystalline and cementitious systems rated for negative water pressure are used for this purpose; the products of our solution partners react within the capillary pores of the concrete and block the passage of water.
Part of the damp and moisture trouble in wet areas comes not from a direct leak but from water absorbed through unprotected surfaces accumulating inside the wall. Blistering paint, crumbling plaster, a musty smell and black staining are the outward signs of that accumulation. A lasting damp remedy starts with a correct diagnosis: is water rising capillary from the floor, seeping through the joints, or is it condensation caused by poor ventilation? EREL Yalıtım makes that distinction during the survey and, where needed, plans interior waterproofing, injection or under-tile renewal together or in stages. Paint and plaster repairs made before the source is dealt with only postpone the problem.
The EREL Yalıtım Difference: Turnkey Work Built to Specification
Most failures in wet area waterproofing are caused not by the material but by the workmanship: membrane applied to an unprimed surface, a skipped corner tape, screed laid before the curing time has passed, or a single coat where two are required. At EREL Yalıtım every job is run to the technical principles set by our engineering team. Materials are chosen according to the manufacturer's technical data sheet and applied to specification; the number of coats, consumption rates and waiting times are set by the system, not by habit.
More than twenty years in the field have built up experience across every scale, from apartment bathrooms to industrial facilities. Our application with a certified crystalline system in the water reservoir of a major airport project is one of the references that shows what detailing discipline means on surfaces in permanent contact with water. We apply the same discipline in the bathroom of a single flat: survey, source diagnosis, system proposal, application and final testing are all handled turnkey by one team. At handover we provide an application report documenting which material was applied, at which detail and in how many coats — so the work remains traceable whatever happens later.
Our Application Process
- 1
Survey and Source Diagnosis
The space is inspected on site; if there is a leak, we establish whether the source is the plumbing or missing waterproofing. Substrate type, intensity of use and detail points are assessed, the appropriate system is selected and a written quotation based on measured quantities is prepared.
- 2
Surface Preparation
Existing tiling and, where necessary, the screed are removed; the surface is cleared of dust, grease and loose particles. Defective screed areas are made good with repair mortar so the substrate is sound and even enough for the waterproofing application.
- 3
Detailing Work
Flexible sealing tapes are installed at wall-floor junctions and corners, pipe collars at penetrations and the correct components around the floor drain. These points, where most leaks begin, are secured before the membrane is applied.
- 4
Priming
A primer matched to the chosen system is applied to balance the absorbency of the substrate and ensure full adhesion of the membrane. The primer's drying time is observed as stated in the manufacturer's technical data sheet.
- 5
Membrane Application
The waterproofing membrane is applied in at least two coats, each at right angles to the previous one. Coat thicknesses and total consumption are kept to the values the system prescribes; in heavily wetted zones such as the shower area, the waterproofing is carried up the wall to the required height.
- 6
Inspection and Flood Test
Once the application has cured, the surface is checked with a ponding test; the drain and detail points are inspected separately. If the test result is positive, the surface is ready for tiling.
- 7
Protection and Handover for Tiling
Tile adhesive and the floor covering are installed without damaging the waterproofing layer. On turnkey projects EREL Yalıtım completes the entire works including the ceramic tiling and hands the job over with an application report.
Frequently Asked Questions
How much does wet area waterproofing cost in Istanbul?
The price depends on the floor area, whether the existing tiling has to be removed, the number of detail points and the waterproofing system selected — which is why quotes given sight unseen are misleading. EREL Yalıtım provides a free site survey: we inspect the space in person and prepare a written quotation based on exact measured quantities.
Can a bathroom be waterproofed without removing the tiles?
In limited cases it is possible to intervene without removing the tiles, using grout renewal or injection methods; these are, however, mostly temporary or localised fixes. A permanent result is achieved by lifting the covering and rebuilding the under-tile waterproofing to specification. At the survey we tell you plainly which approach fits your situation.
Are the walls waterproofed too, or only the floor?
Yes. The entire floor and all wall-floor junctions are always waterproofed; around showers and bathtubs the waterproofing is carried up the wall to splash height. Locally wetted zones such as washbasin and tap surrounds are also detailed. An application confined to the floor is left unprotected against water entering through wall joints.
Can interior waterproofing replace exterior waterproofing?
Where the water cannot be reached from outside — basements and terraced buildings are the typical cases — interior waterproofing is the correct engineering solution, applied with crystalline and cementitious systems rated for negative water pressure. Where the outer face is accessible, positive-side waterproofing takes priority. The right approach is decided at the survey, based on the direction the water comes from.
How long does the work take, and can the bathroom be used meanwhile?
In a standard residential bathroom the whole process — stripping, waterproofing and re-tiling — usually takes between a few days and a week; the main factor is the curing time between coats. The room cannot be used during the works. After the survey we share a clear work schedule based on the scope of the job.
Does waterproofing solve damp and mould permanently?
If the source of the damp is a leak or moisture rising from the floor, waterproofing with the correct system solves the problem permanently. If the source is condensation caused by poor ventilation, ventilation measures are needed alongside the waterproofing. We make that distinction at the survey and plan a remedy aimed at the source rather than covering it up with paint and plaster repairs.