Types of Waterproofing: Coatings, Membranes, Penetrating

How coating, sheet membrane, penetrating and injection waterproofing work, where each is used, and what determines the choice.

Waterproofing is the invisible part of a building that causes the most expensive consequences. A layer that is badly chosen or poorly applied shows up years later as damp patches, mould, flaking plaster and corroded reinforcement. To choose correctly, you first need to understand how water is acting on the structure, and then how the materials work.

How water acts on a structure

The single word "waterproofing" covers very different loads:

• running surface water — rain, shower water, water ponding on a balcony;
• ground moisture — damp drawn into the structure by capillary action;
• water under pressure — groundwater pressing against basement walls when the water table is high;
• vapour — warm, humid air condensing inside a cold structure.

Each type of waterproofing answers one or more of these loads. Vapour is a separate subject handled with a vapour barrier; confusing it with waterproofing is a typical mistake.

Coating (liquid-applied) waterproofing

With coating systems, material in liquid or paste form is applied with a brush, roller or trowel, and once cured forms a continuous, seamless layer. The main types are bitumen and polymer-modified bitumen mastics, polymer-cement slurries and elastic polyurethane or acrylic coatings.

Their advantage is easy application on complex shapes, corners and pipe penetrations. They are widely used in bathrooms and showers, on balconies, small terraces and foundation walls. Their weakness is that thickness depends on the applicator: if the coat is too thin or uneven, protection suffers. That is why following the manufacturer's number of coats, coverage rate and drying time between coats is essential. Elastic tape or reinforcing mesh is added at corners and joints.

Sheet membrane waterproofing

Here, factory-made membranes are bonded, torch-welded or mechanically fixed to the surface. Polymer-modified bitumen sheets, synthetic membranes such as PVC and TPO, and bentonite mats belong to this group.

Membrane thickness is set in the factory, so quality is more consistent. Membranes are preferred on large, simple surfaces such as flat roofs, large terraces and foundation slabs. The risky areas are seams and junctions: overlap width, weld quality and the detailing at parapets and pipe penetrations decide the reliability of the whole system. The membrane must be protected from mechanical damage — a screed poured on top, protection boards or geotextile serve this purpose.

Penetrating (crystalline) waterproofing

Penetrating products are applied to concrete and cement-based surfaces. Their active ingredients enter the pores of the concrete, form crystals in the presence of moisture and block the pores. As a result, the concrete itself becomes more resistant to water.

An important advantage is that they can be applied from the inside — the side opposite the water pressure. That makes them useful for existing basements, water tanks, swimming pools and lift pits. Their limitation is that they work only on sufficiently dense concrete and cement-based surfaces; on brickwork, aerated concrete or cracked, moving structures they are not reliable on their own.

Injection waterproofing

With injection, holes are drilled into the structure and a special compound is pumped in under pressure. This is used to seal cracks and cold joints or to create a horizontal barrier in a wall. Polyurethane resins that foam quickly are used against active water ingress, while silicone-based products are used to cut off rising damp. Injection is mostly repair and remedial work, carried out after diagnosis.

What decides the choice

There is no single "best" waterproofing. The decision comes from these questions:

• How does water act: running, damp or under pressure?
• What is the structure made of: concrete, brick, plasterboard?
• Is it new construction or an existing building?
• Which side can be reached: the outside, or only the inside?
• Does the structure move, and is there a risk of cracking?
• What goes on top: tiles, screed, soil, foot traffic?

In practice systems are often combined — for example, an external sheet membrane on a foundation, a penetrating layer inside and special tapes at joints. Just as important as the material itself are surface preparation and the detailing of junctions.

In its construction and renovation work Zaferoğlu İnşaat selects the waterproofing solution according to the type of structure and the water load.