Article

Materials, selection, execution – foundation waterproofing (part 1)

Waterproofing materials and their applications

Introduction: decisions from the ground up

Choosing the right foundation waterproofing is crucial for the durability of the entire building – a mistake at this stage can mean costly repairs in the future. Importantly, however, the right choice does not start with the material, but with an analysis of the soil and water conditions and the determination of the water exposure class.

In this series of articles, we will dispel the myths about foundation waterproofing and show you how to make informed technical decisions that will save you time, money and stress for years to come. In part I of our series, we explain how to correctly translate soil and water conditions into the selection of light or heavy insulation and which systems work best in each DIN 18533 class. This article kicks off a series of practical design and implementation tips that will help you avoid common mistakes.

Step-by-step selection algorithm

Structural reliability criteria

Structures and structural elements should be designed, constructed and maintained in such a way that they are suitable for use in an economical manner throughout their service life [10]. In particular, structures should meet the following requirements with an appropriate degree of reliability:

They should adequately transfer all expected impacts (requirements resulting from serviceability limit states);
They should transfer extremely high and frequently repeated impacts occurring during construction and anticipated use (requirements resulting from damage (ultimate) limit states);
They should not show damage disproportionate to the original cause as a result of events such as flooding, landslides, fire, explosion, or as a result of human error (structural resistance requirement).
The appropriate degree of reliability shall be determined taking into account the possible consequences of loss of reliability, as well as the cost, scope of effort and activities necessary to reduce the risk of damage. Measures to be taken to achieve the appropriate degree of reliability include:
selection of the load-bearing structure, proper design and analysis;
implementation of a quality policy;
inclusion of maintenance and durability requirements in the design; application of protective measures (...).

Selection algorithm: from research to system

The selection of the technological and material solution for waterproofing (not the material itself) is one of the key factors affecting the service life and comfort of use of a building. Regardless of the type and use of the facility (underground garage, public building, industrial building, residential building), the criteria for selecting waterproofing materials will be identical.

When analysing the causes of seepage and leaks, the criteria and their weighting can of course be differentiated, but in each case a certain cause-and-effect sequence can be identified, starting with a lack of analysis of soil and water conditions and the proposed structural design of the foundation, and ending with workmanship that does not comply with state-of-the-art and current technical knowledge.

Analysis factors: conditions and details

The concept of waterproofing foundations can be illustrated using the algorithm shown in the diagram below.

The necessary analysis should take into account:

soil and water conditions,
presence of aggressive groundwater,
building’s structural design (type of foundation, presence of a basement, height of the basement storey, etc.),
presence of expansion joints, pipe passages and penetrations, etc., which are difficult and critical areas.

When designing waterproofing solutions, the following factors should also be taken into account:

type and condition of the substrate (evenness, possibility of cracks, moisture, drying and stabilising, etc.),
application possibilities in a specific facility,
compatibility of waterproofing materials (possibility of making tight joints),
technology for sealing pipe penetrations, expansion joints, etc.

Let us analyse its individual elements.

Geotechnical investigations and filtration coefficient k

Analysis of soil and water conditions is the first, basic element of the technological activities necessary for the correct design and implementation of water protection for a structure. In terms of water permeability, soils can be classified as follows:

very highly water-permeable: k > 10⁻² m/s,
highly water-permeable: k from 10⁻² m/s to 10⁻⁴ m/s,
water-permeable: k from 10⁻⁴ m/s to 10⁻⁶ m/s,
poorly permeable (low permeability): k from 10⁻⁶ m/s to 10⁻⁸ m/s,
very poorly permeable (very low permeability) k from 10⁻⁸ m/s to 10⁻⁹ m/s,
almost impermeable: k < 10⁻⁹ m/s,

where the criterion is the above-mentioned soil permeability coefficient k.

The classification of soils in terms of water permeability is shown in the table opposite. Soils with k > 10⁻⁴ m/s are considered highly permeable, while soils with k ≤ 10⁻⁴ m/s are classified as poorly permeable, which means that temporary accumulation of rainwater should be expected.

Soil type (loose clastic rock)	Soil permeability coefficient (filtration coefficient) k [m/s]
Rubble, gravel, coarse sand	10 ÷ 10⁻³
Mixed-grain sand	10⁻³ ÷ 10⁻⁴
Fine-grain sand	10⁻⁴ ÷ 10⁻⁵
Silty and clayey sand	10⁻⁵ ÷ 10⁻⁶
Clays, sandy loams	10⁻⁶ ÷ 10⁻⁸
Loams, clay loam	>10⁻⁸

Water exposure and type of insulation

The classification of soils in terms of water permeability results in a division into water exposure levels and types of insulation.

Water exposure levels

exposure to moisture contained in the soil (Fig. 1)
The condition for its occurrence is the foundation of the building in non-cohesive and well-permeable soil (the possibility of rapid infiltration of rainwater into the ground below the foundation level of the building and the exclusion of high groundwater levels) – soil water permeability coefficient (filtration coefficient) k > 10⁻⁴ m/s.

non-standing rainwater exposure (Fig. 2)
This occurs when cohesive soil is present at and below the foundation level, preventing rapid infiltration of rainwater (k ≤ 10⁻⁴ m/s), with excess water being drained away by an effective drainage system.

standing rainwater exposure (Fig. 3)
This occurs when the building is founded in soils with low water permeability (k ≤ 10⁻⁴ m/s), which results in hydrostatic pressure on the waterproofing due to periodically accumulating rainwater. The maximum groundwater level must be no more than 30 cm below the bottom of the foundation slab (strip footings).

pressurising water exposure (Fig. 4)
This situation occurs when the groundwater level is high (above the foundation level) or when the foundations are exposed to prolonged pressure from water.

Light or heavy insulation?

Types of insulation:

damp-proof insulation (light insulation) is only recommended for foundations exposed to moisture. It can also be used for foundations exposed to non-standing rainwater, provided that a durable and effective drainage system is installed to remove excess rainwater.
waterproof insulation (heavy insulation) is used when there is standing rainwater and pressurised water.

Common mistakes in exposure classification

A common mistake is to uncritically assume moisture exposure in situations where soil tests do not reveal high water levels in the surrounding soil (this often results in moisture or even leaks into the building, which are difficult and costly to remove). Soil stratification i.e. the presence of layers that are difficult to permeate by water in the subsoil (see figure) clearly indicates the need for heavy-type insulation.

Waterproofing materials – applications and limitations

The above division into damp-proof and waterproof insulation must be assigned to the type of waterproofing materials. Details are shown in the table.

Type of waterproofing material	Damp-proof insulation	Waterproof insulation	Remarks
Asphalt binders	+	-	Binder crumbles when passing through zero level
Asphalt solutions and emulsions	+	-	Only on vertical surfaces
Bitumen compounds	+	±	Sensitivity to zero-crossing level for non-modified compounds
Polymer-bituminous thick-layer sealing compounds (KMB compounds)	+	+	With restrictions on horizontal surfaces
Sealing slurries (micro-mortars)	+	+	Rigid slurries to a limited extent; Flexible slurries – also used in the plinth area
Hybrid sealing compounds	+	+	Also used in the plinth area (min. layer thickness 2 mm)
Crystalline sealing mortars	±	+	The structure should be designed as for waterproof concrete
Heat-weldable polymer-bituminous felts and self-adhesive membranes	+	+	Polymer-modified, not ‘with polymer additives’
Binder-bonded bituminous felts	+	±	Cardboard-reinforced bituminous felt must not be used
Plastic and rubber foils/me mbranes	+	+	The building must be designed for foil insulation
Bentonite mats	±	+	Require additional pressure to ensure effectiveness

Designed parameters and effectiveness

The classification of waterproofing materials according to moisture/water exposure presented in the table is very general. The applicability (effectiveness) of a material or technological and material solution is also influenced by the essential characteristics (parameters and properties) of waterproofing materials. This issue, which is generally omitted in Polish technical literature, is precisely addressed by the DIN 18533 series of standards ([1]÷[3]) concerning the waterproofing of parts of buildings in contact with soil. When determining moisture/water exposure classes, they take into account:

ground level,
calculated highest groundwater level (HGW), i.e. the maximum groundwater level to be assumed for the dimensioning of waterproofing,
flood water level or the highest hazardous water level (HHW), i.e. the water level corresponding to flooding or waterlogging – when the above-ground parts of the building may be subjected to periodically occurring water exerting hydrostatic pressure.

Water exposure classes according to DIN 18533 (W1–W4) in practice

The above-mentioned moisture/water exposure classes are defined as follows:

W1: Ground moisture and non-pressurising water (water acting without hydrostatic pressure)

W1.1-E – moisture exposure of walls and foundation slab. This occurs when a building/structure is founded on permeable soil and the foundation trenches have also been backfilled with water-permeable soil (k > 10⁻⁴ m/s). The groundwater level must be at least 50 cm below the horizontal insulation plane or the lower edge of the vertical insulation, and the water level in the ground must not rise, regardless of the cause. This is essentially identical to the variant shown in Fig. 1.
W1.2-E. The difference from variant W1.1-E lies in the permeability of the soil and the presence of drainage. The building is founded on poorly permeable soil (k > 10⁻⁴ m/s), but rainwater is collected by drainage. It is an absolute requirement that the groundwater level is at least 50 cm below the horizontal insulation plane and that the water level in the ground does not rise, regardless of the cause. This is known as non-pressurising water exposure. This variant is essentially identical to the one shown in Fig. 2.

W2: Moderate and intense water pressure

W2.1-E – moderate water exposure. This variant occurs when:
- case 1: We are dealing with a temporary exposure to standing rainwater. The building is founded on poorly permeable soil, without drainage, the lowest horizontal plane of waterproofing is no deeper than 3 m below ground level and above the groundwater level, and the level of standing rainwater (accumulated, e.g. as a result of precipitation) is not higher than the ground level (water column pressure ≤ 3 m, calculated groundwater level/flood water level is equal to ground level).
- case 2: We are dealing with groundwater exposure here. The calculated groundwater level is a maximum of 3 m above the lowest horizontal insulation level. There is no specific soil permeability coefficient here.
- case 3: We are dealing with flood water exposure. Flood water impact – up to 3 m water column (flood water level is max. 3 m above the lowest horizontal insulation level)
W2.2-E – intense water exposure. This variant occurs when:
- case 1: We are dealing with a temporary exposure to standing rainwater. The building is founded on poorly permeable soil without drainage, the lowest horizontal plane of the waterproofing is more than 3 m below ground level, and the level of standing rainwater (accumulated, e.g. as a result of precipitation) is not higher than ground level (water column pressure > 3 m).
- case 2: We are dealing here with groundwater or floodwater exposure. The calculated groundwater/floodwater level is 3 m or more above the lowest horizontal insulation level.

W3: Buried suspended slabs

W3-E is the non-pressurised water exposure on buried suspended slabs. This case applies to suspended slab structures that are not loaded with either standing water or ground/flood water (the lowest point of the structure must be at least 30 cm above the calculated groundwater/flood water level) and the maximum accumulation of runoff water must not exceed 10 cm. Rainwater must be drained by water-permeable layers and/or an appropriate slope. Otherwise, this variant should be treated as W2.2-E

GOK – ground level,
HGW – calculated groundwater level
HHW – calculated flood water level

W4: Plinth area and capillary rise

W4-E is the exposure caused by splash water in the plinth area and capillary action in internal walls and walls in contact with the ground. The standard clearly defines the plinth area: 20 cm below and 30 cm above ground level, with the proviso that this is possible unless the calculated groundwater and/or flood level indicates otherwise (in which case W2-E applies).

GOK – ground level
HGW – calculated groundwater level
HHW – calculated flood water level

Variants W2.1-E (moderate water exposure) and W2.2-E (intense water exposure) correspond in principle to the exposure of standing rainwater and pressurising water in the ground (the building ‘stands in water’). The difference lies in the depth of foundation and maximum water pressure, which results in different recommendations regarding the type of material and parameters of waterproofing coatings.

The starting point for assigning a material to a specific moisture or water exposure class is not the requirements of the PN-EN series of standards, but the definition of the minimum or maximum parameters (essential characteristics) of waterproofing materials or systems.

Selection of materials according to DIN 18533

The tables below show the classification according to the standard [1] of waterproofing materials to the class of water impact and the element being sealed. It should be noted that the above-mentioned standard [1] limits the use of KMB compounds (to water pressure not exceeding 3 m) as well as the use of slurries in the ground in practice to damp-proof insulation. From a technical point of view, the parameters of KMB compounds and slurries from NEXLER, due to their tightness of 50 m of water column, allow them to be used in virtually any exposure of foundations under water pressure.

Types of waterproofing materials used for water impact class:

W1-E [1]

Sealed element	Type of material
Base slab	Rolled bituminous and polymer-bituminous materials
	Rolled plastic and rubber materials
	PMBC (KMB) – compounds, asphalt-mineral mixtures
	Mineral slurries
Foundation wall	Rolled bituminous and polymer-bituminous materials
	Rolled plastic and rubber materials
	PMBC (KMB) compounds
	Mineral slurries

W2-E [1]

Water pressure	Type of material
Up to 3 m	Rolled bituminous and polymer-bituminous materials
	Rolled plastic and rubber materials
	PMBC (KMB) compounds,
Above 3 m	Rolled bituminous and polymer-bituminous materials
Above 3 m	Rolled plastic and rubber materials

W3-E [1]

Sealed element	Type of material
Buried suspended slab	Rolled bituminous and polymer-bituminous materials
	Rolled plastic and rubber materials
	PMBC (KMB) compounds
	Liquid plastics
	Weldable polymer-bituminous felts combined with asphalt-mineral mixtures

W4-E [4]

Sealed element	Type of material
Plinth areas and insulation under walls	Rolled bituminous and polymer-bituminous materials
	Rolled plastic and rubber materials
	Flexible sealing slurries
	PMBC (KMB) compounds (except for insulation under walls)
	Liquid plastics

Design and execution – critical decisions

The design of the underground part of a structure is a result of the adopted building design concept, load analysis, type, condition and strength parameters of the subsoil, as well as soil and water conditions. Apart from cases where a structure is founded on piles, there are generally two types of foundation:

the structure is founded on a foundation slab
the structure is founded on strip footings and footings, and the floor is made in the form of a separate slab on the ground.

The insulation itself can be made as a damp-proof or waterproof coating, and white tub solutions (waterproof concrete structures) are also used.

The most common mistakes and risks

Light-type waterproofing – savings or risk?

Due to the above, the design and execution of waterproofing coatings cannot be left to chance. Moisture exposure (if it actually occurs, which, contrary to appearances, is quite rare) is not a sufficient reason to use only light waterproofing. A special case is the foundation of buildings on a foundation slab. This applies to both single-family buildings (it is common for them to be founded on a slab, at the level of the surrounding terrain) and public utility, industrial buildings or underground garages. A common feature of slab foundations is the presence of waterproofing under the foundation slab. This means that there is no access to the waterproofing coating under the slab. The insulation must therefore be 100% effective, regardless of moisture/water exposure and mechanical loads.

Underground garages: recommended systems

In the case of underground garages, it is generally a mistake to install damp-proof insulation. It cannot be ruled out that the deep foundations of newly constructed buildings may disrupt the existing course of underground watercourses and change the soil and water conditions, resulting in water exposure. Therefore, in practice, the following are used to protect underground garages against water:

rolled bituminous materials such as polymer-bituminous felts or self-adhesive membranes
seamless mineral and bituminous materials (KMB compounds, hybrid compounds, flexible slurries)
rolled plastic and rubber materials
white tub-type structures

In the case of residential buildings founded on a slab laid horizontally on the ground, in addition to waterproofing issues, there are also issues of adequate thermal insulation (thermal insulation can be located under the foundation slab).

Material parameters vs standards

However, this does not mean that each of the above-mentioned materials is suitable for waterproofing coatings. Very rarely, if ever, are the parameters of waterproofing materials (such as adhesion, flexibility/crack bridging ability, resistance to mechanical loads, etc.) analysed, while within the same group of materials there may be significant differences in essential characteristics (parameters/properties).

The situation is not helped by the lack of current standards, guidelines and recommendations specifying the rules for constructing waterproofing systems. Although European standards define certain requirements for waterproofing materials, dividing them into classes, they say nothing about the applicability of the material (and in some cases are even misleading). This is because it does not result from meeting the requirements of the standards, but from an analysis of the boundary conditions and technical properties and parameters of materials protecting against water.

NEXLER waterproofing materials are designed with features and properties that aim to:

maximise ease of application,
expand application possibilities
increase safety of use, even in extreme operating conditions, by:
- adding features and parameters beyond those typically associated with a given product group,
- adding or expanding functional features that are important during use and increase the service life of solutions.

What’s next in the series?

The following parts will discuss issues related to bituminous roll materials and seamless materials.

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Bibliography

[1] DIN 18533-1:2017-07 Abdichtung von erdberührten Bauteilen Abdichtung von erdberührten Bauteilen - Teil 1: Anforderungen, Planungs- und Ausführungsgrundsätze

[2] DIN 18533-2:2017-07 Abdichtung von erdberührten Bauteilen - Teil 2: Abdichtung mit bahnenförmigen Abdichtungsstoffen

[3] DIN 18533-3:2017-07 Abdichtung von erdberührten Bauteilen - Teil 3: Abdichtung mit flüssig zu verarbeitenden Abdichtungsstoffen

[4] Richtlinie für die Planung und Ausführung von Abdichtungen mit mineralischen Dichtungsschlämmen, Deutsche Bauchemie e. V. 2020

[5] Richtlinie für die Planung und Ausführung von Abdichtungen mit polymermodifizierten Bitumendickbeschichtungen (PMBC), Deutsche Bauchemie e. V. 2018

[6] Specyfikacja techniczna wykonania i odbioru robót budowlanych. Roboty hydroizolacyjne. Izolacje przeciwwilgociowe i wodochronne części podziemnych i przyziemi budynków. wyd. II, OWEOB Promocja – 2017

[7] Warunki techniczne wykonania i odbioru robót budowlanych. Poradnik projektanta, kierownika budowy i inspektora nadzoru. Praca zbiorowa, Verlag Dashofer, Warszawa 2018

[8] Rokiel M.– Hydroizolacje podziemnych części budynków i budowli. Projektowanie i warunki techniczne wykonania i odbioru robót, wyd. IV, Grupa MEDIUM, Warszawa 2019

[9] Rokiel M. – Poradnik. Hydroizolacje w budownictwie. Projektowanie. Wykonawstwo., wyd.III, Grupa MEDIUM, 2019 r

[10] PN-ISO 2394:2000 Ogólne zasady niezawodności konstrukcji budowlanych

mgr inż. Maciej Rokiel [MSc, Eng.] is a renowned mycological and construction expert and engineer with over 20 years of experience in protecting buildings against water and biological corrosion. He is the author of acclaimed publications, such as ‘Hydroizolacje w budownictwie’ (‘Waterproofing in Construction’) and ‘Renowacje obiektów budowlanych’ (‘Renovation of Buildings’), which are compendiums of knowledge for designers, contractors, and experts. His achievements include numerous expert opinions, articles and e-books published in prestigious industry titles such as ‘Izolacje’ (Insulation) and ‘Inżynier Budownictwa’ (Construction Engineer). He specialises in the diagnosis of dampness and salinity in walls, the design of waterproofing and the renovation of problematic buildings, and his works are widely cited in technical literature.