Foundation and Basement Waterproofing

Every building element in contact with the ground is exposed to water and moisture loads. Where the groundwater table is high, basement walls are permanently exposed to pressurized water; even where the table is low, water accumulating in the soil after rainfall and capillary moisture reach the interior through the porous structure of concrete. Concrete is not a watertight material: cold joints, form-tie holes, shrinkage cracks and service penetrations all form natural pathways for water.

In every building with a basement — especially where basement floors are used as housing, parking, shelters or storage — foundation waterproofing is a job that must be resolved at the design stage. Current waterproofing codes and technical specifications also generally call for waterproofing of ground-contact elements in new buildings. Retrofit interventions are both more expensive and technically more limited, which is why the right system should be selected together with the geotechnical survey data before construction begins.

In existing buildings, the following symptoms point to a foundation-related water problem and call for a technical inspection without delay:

Tanking means wrapping every below-ground surface of the structure — the underside of the foundation, its side faces and the basement walls — in a single continuous waterproofing envelope. The aim is a barrier that leaves water no point of entry. Under hydrostatic pressure, when the groundwater table sits above foundation level, tanking is the preferred approach: water can find the smallest unprotected area and work its way into the structure through it.

Under-slab waterproofing starts with membrane layers laid over the blinding concrete. Seams are joined with the overlaps defined in the specification, lap allowances are left at the raft edges to turn up onto the walls, and the membrane is covered with a protective screed so that rebar and formwork can proceed. Once the basement walls are cast, the waiting laps are joined to the vertical waterproofing, so that the under-slab and wall systems act as a single continuous layer. These junctions are the most critical details of the whole system, and most of the workmanship failures seen on site occur exactly here.

On well-drained ground without hydrostatic pressure, more economical details concentrating on the foundation perimeter and wall faces can be designed instead of full tanking. The required scope is decided from the geotechnical survey, the groundwater level and the intended basement use; EREL Yalıtım settles this decision on data during the site survey.

There is no single correct material for basement wall waterproofing; the right system is chosen according to the water load, ground conditions, application surface and construction schedule. Bitumen-based sheet membranes provide controlled layer thickness and high resistance to water pressure; cementitious elastic coatings offer seamless application over complex details and crack-bridging capability. Crystalline systems react within the capillary pores of the concrete to create integral watertightness and can also work from the negative side.

Under the slab, pre-applied Proof membranes stand out: laid over the blinding concrete, the membrane bonds fully to the concrete cast on top and prevents water migration between the waterproofing and the structure. EREL Yalıtım recommends the system best suited to the project — with its reasoning — from leading global manufacturers. The main system options can be summarized as follows:

Whichever system is selected, the wall waterproofing must be protected with drainage boards before backfilling, and a drainage line arranged at foundation level to reduce the water load on the membrane. Where the waterproofing is left unprotected, mechanical damage during backfilling can render the entire system useless.

In new construction, successful foundation waterproofing depends on integrating it correctly into the site programme. EREL Yalıtım takes over coordination with the blinding, rebar and formwork crews, and plans the under-slab installation and wall application without delaying the schedule. The work follows the technical specification; overlaps, layer counts and consumption rates are checked at every stage and documented with photo reports. Thanks to the turnkey working model, the client — whether a property owner or a B2B contractor — deals with a single point of responsibility.

In existing buildings, water ingress from the foundation is resolved in one of two ways. Where excavation around the building is possible, the walls are exposed and the waterproofing renewed from the positive side — the most permanent method. Where excavation is not possible, water-bearing cracks, cold joints and expansion joint lines are sealed from the inside using crystalline mortars and polyurethane or epoxy injection. The method is chosen only after the source of the water ingress has been identified.

EREL Yalıtım has applied this approach on large-scale projects as well: thousands of square metres of Proof Membran and Ravaproof have been installed at industrial facilities, and a crystalline waterproofing system was used in the water reservoir of a major airport project. Carried out under engineer supervision, these projects were delivered with the same technical discipline from system selection to detailing.