What is cementitious waterproofing?
Cementitious waterproofing is a layer of polymer-modified cementitious mortar a few millimetres thick, applied by trowel, brush or mortar pump to concrete, masonry and cement screeds. The cement provides bond to the mineral substrate and water resistance, while the polymer provides density, adhesion and, in flexible products, the ability to bridge cracks. These materials are applied to a damp substrate, they are vapour-permeable and, once cured, perform well under tiles, screeds and backfill.
Products are either one-component — a dry mix that is mixed with water — or two-component: the powder is mixed with a liquid polymer component in whole packs, without adding water. Two-component products are usually more flexible and more consistent in their properties, because the ratio is set at the factory.
Rigid and flexible products
- Rigid (polymer-modified cementitious) — a strong watertight layer for concrete and masonry that do not move: foundations and basements, vessels, manholes, pits. They do not bridge cracks in the substrate — if the concrete cracks, so will the layer. An example in the catalogue is SikaTop Seal-107.
- Flexible (cement-acrylic) — remain flexible after curing and bridge cracks in the substrate: balconies and terraces, wet rooms, swimming pools, channels, thin-walled tanks, structures with shrinkage and thermal cracks. These are Mapelastic, Mapelastic Smart, Mapelastic Foundation, SikaTop-525 Seal and Fosroc Brushbond.
Flexible products also differ from one another: some are designed for use in frost — according to its data sheet, Mapelastic remains flexible down to −20 °C; others for negative water pressure, such as Mapelastic Foundation (up to 1.5 atm); still others for exposed use: SikaTop-525 Seal is white and UV-resistant, but even with this product, surfaces with foot traffic are covered with a screed or tiles.
Where it is used
- foundations and basement walls — from the outside during construction; from the inside, only with products designed for negative pressure;
- bathrooms, shower rooms, toilets, laundries, commercial kitchens — under tiles;
- balconies, terraces and accessible roofs — under tiles or a screed;
- swimming pools, fountains, ornamental ponds;
- concrete channels, flumes, process water tanks, and for drinking water only materials with the appropriate documents (see “Tanks, swimming pools and treatment plants”).
How to choose a product
Substrate movement
If the substrate may crack — a young screed, a thin balcony slab, temperature fluctuations on a terrace, vibration — a flexible product is needed, and junctions between different materials, corners and joints are additionally covered with tapes. A rigid layer is appropriate on massive concrete and masonry that do not move.
Side and water pressure
A cementitious coating works best on the positive side, and the permissible head is stated in the data sheet: for Fosroc Brushbond, for example, up to 7 m of water head depending on the thickness. On the negative side, only materials for which the manufacturer states such a pressure are used, and only within its limits — for Mapelastic Foundation, this is 1.5 atm.
Tiles, backfill or an exposed surface
For use under ceramic tiles, the material must be tested to EN 14891. This standard covers liquid-applied waterproofing products beneath tiles bonded with adhesive — polymer-modified cementitious, dispersion and reaction resin products — for external wall and floor finishes and for swimming pools. The class designation states the material type and the additional properties — for Mapei’s polymer-modified cementitious products, for example, CM O1 P or CM O2 P. The Mapei data sheets also give the requirements of the standard: crack bridging of at least 0.75 mm and a bond strength of at least 0.5 N/mm², including after contact with water, heat ageing, freeze–thaw cycles, lime water and chlorinated water. The tile adhesive is chosen from the same manufacturer as the waterproofing — this way the compatibility is confirmed.
Under backfill, the layer is protected from stones and machinery, and exposed surfaces from UV light and abrasion: most of the cementitious products in the catalogue are designed to be covered afterwards.
Climate and working conditions
The lower application temperature limit for the products in the catalogue is +5…+8 °C and the upper limit is +30…+40 °C, depending on the material. In heat and wind the layer quickly loses water, so the substrate is dampened and the fresh coating is protected from the sun.
What the system consists of
- A prepared substrate — sound, clean, rough, with blowholes and cracks repaired.
- Tapes and collars — at corners, at wall-to-floor junctions, along movement and structural joints, around floor drains and pipes. They are embedded in the first coat; Mapeband Easy tape, for example, is designed specifically for use in cementitious waterproofing.
- The first coat with an alkali-resistant glass-fibre reinforcing mesh or fabric — on balconies and terraces, in swimming pools and tanks, on cracked substrates.
- The second coat — after the first has set, up to the total thickness specified in the data sheet; for most of the products in the catalogue, this is about 2 mm.
- Protection or finish — tiles laid in adhesive, a screed, a protective membrane under backfill.
Substrate preparation
- Laitance, dirt, oil, old paint and weak layers are removed mechanically or with pressurised water; smooth concrete is roughened.
- Blowholes, spalls and deteriorated concrete are reinstated with repair mortars — see “Concrete repair mortars”; active leaks are stopped beforehand.
- Internal corners are rounded or filled with a fillet, and external corners are smoothed.
- The substrate is dampened to a matt damp condition without puddles: on dry concrete, the mortar loses water and does not develop its bond strength.
Common mistakes
- One thick coat instead of two — shrinkage cracks and delamination.
- Adding water to a two-component product or mixing part packs — the properties deviate from those declared.
- No tapes at corners and joints: the layer cracks along the wall-to-floor junction in the very first season.
- A rigid product on a balcony or terrace, where the substrate moves with temperature fluctuations.
- A positive-side product used inside a basement with water under pressure.
- The tiles were laid before the time given in the data sheet or with an adhesive that is not compatible with the waterproofing.
- A trafficked or exposed surface has been left without a finish, although the material is not designed for this.
See also: waterproofing — overview, penetrating waterproofing, liquid-applied membranes, joint waterproofing.
Materials in the catalogue
- SikaTop Seal-107 — Sika — polymer-modified cementitious waterproofing slurry for concrete and masonry, 1.5–2 mm.
- SikaTop-525 Seal — Sika — white UV-resistant flexible cement-acrylic waterproofing for tanks, pools and wet areas.
- Mapelastic — Mapei — flexible two-component cementitious waterproofing for balconies, terraces, bathrooms and pools.
- Mapelastic Smart — Mapei — highly flexible cementitious waterproofing for channels, tanks, pools and terraces.
- Mapelastic Foundation — Mapei — flexible cementitious waterproofing for foundations and basements, positive and negative pressure.
- Fosroc Brushbond — Fosroc — acrylic polymer-modified cementitious protective and waterproof coating for concrete and masonry.
- Skrepa 2K Elastichnaya — Penetron — two-component flexible cementitious waterproofing coating bridging cracks up to 1.5 mm.
Frequently asked questions
Can cementitious waterproofing be applied to a damp substrate?
Yes, cementitious products actually need a damp substrate: it is dampened before application to a matt condition without puddles. They must not be applied over standing water or to a substrate with an active leak — the leak is stopped first.
When can tiles be laid?
After the time given in the data sheet. For Mapelastic, for example, no earlier than 5 days, or after 24 hours in good weather on a dry substrate. The adhesive is chosen from the same manufacturer as the waterproofing.
How does cementitious waterproofing differ from penetrating waterproofing?
A cementitious coating is a separate layer on the surface: flexible products bridge cracks, but the layer can be damaged and needs protection. A penetrating compound works in the pores of the concrete itself and does not delaminate, but it does not bridge cracks that move. Sometimes the two are combined: the penetrating compound densifies the concrete, and a flexible coating covers the cracked areas.
Is cementitious waterproofing suitable for a swimming pool?
Yes, provided that the material has been tested to EN 14891 for contact with chlorinated water and is finished with tiles or mosaic. Details — cast-in items, drains, joints — are covered with the system tapes and collars.
We will select cementitious waterproofing and a set of tapes and meshes for your project — call us or message us on WhatsApp/Telegram: +998 94 094 52 27.