- Article
Materials, selection, execution – foundation waterproofing (part 2)
Selection of bituminous felts for water conditions (exposure classes)
Material selection
Selecting the right waterproofing material is not just a matter of determining the water exposure class – a detailed analysis of the available products is equally important. Bituminous felt is a material that has been popular in construction for years, especially for protecting foundations against moisture and groundwater. Its use allows for effective protection of structures, preventing corrosion and degradation of construction materials. Bituminous felts available on the market differ not only in the type of bitumen or reinforcement, but above all in their performance parameters. It is these properties that play a key role in ensuring the durability of insulation under specific operating conditions.
In this part of our series, we explain how to correctly interpret standards and manufacturers’ declarations. We explain the differences between bituminous felts and polymer-bituminous felts, and discuss the role of the reinforcement in the construction of the material. In addition, we indicate which parameters are worth paying special attention to in order to consciously choose a solution that guarantees the longevity and reliability of the structure.
The importance of technical documentation
It is very important to prepare technical documentation carefully. Detailed drawings of specific elements should be prepared at the design stage, e.g. connections between vertical and horizontal insulation, methods of protection of the plinth area, sealing expansion joints, pipe penetrations, etc. This requirement also includes the need to select materials for waterproofing parts located in the ground, taking into account the required parameters.
Essential characteristics of bituminous felts
Rolled materials for waterproofing in soil (bituminous felts) are declared to comply with the PN-EN 13969 standard [1]. This standard defines the following essential characteristics of bituminous felt:
- watertightness
- watertightness after artificial ageing
- watertightness after exposure to chemicals
- resistance to static loading
- tensile mechanical properties
- resistance to tearing (nail shank)
- resistance to impact
- flexibility at low temperatures (pliability)
- joint strength
- water vapour transmission properties
- reaction to fire
- length
- width
- thickness
- mass per unit area
- straightness
- dangerous substances
- visible defects
MLV and MDV – limit values versus declared values
Very rarely, if ever, are the parameters of waterproofing materials analysed (adhesion, flexibility/crack bridging ability, resistance to mechanical loads, etc.). Meanwhile, apart from watertightness at 2 kPa (20 cm water column) and 60 kPa (6 m water column) declared for bituminous felts as damp-proof and waterproof insulation, respectively, the above-mentioned standard does not set any requirements for essential characteristics. It only uses the following values:
limit values, marked with the symbol MLV – this is a specific limit value (minimum or maximum) set by the manufacturer, which must be achieved in tests,
declared values, marked with the symbol MDV – this is a specific value declared by the manufacturer (the result of a specific test, the value of a specific parameter), given with an assumed tolerance.
However, the standard does not specify the parameters that a particular material must have in order to perform its function under specific boundary conditions (e.g. under a specific moisture/water exposure, for a specific application, etc.).
The parameters and characteristics of bituminous felts depend primarily on the type and properties of the bitumen (oxidised, SBS-modified or APP-modified asphalt) and the reinforcement material.
Types and properties of bitumen
The type of asphalt has the greatest impact on the durability and operational effectiveness of the material (resistance to ageing). It also determines water resistance, resistance to weather conditions, temperature (flexibility) and ease of processing and application. For this reason, a distinction is made between bituminous and polymer-bituminous felts. The former is produced on the basis of asphalt without admixtures and additives. This asphalt is characterised by low flexibility and a relatively short service life.
SBS elastomer
(styrene-butadiene-styrene copolymer) gives the bituminous felt dimensional stability, good adhesion to the substrate and considerable flexibility even at very low temperatures (down to -25°C). SBS-modified bituminous felt is designed for waterproofing structures used in the harshest conditions, in places where subsequent repair is impossible (e.g. under the base slab). The amount of modifiers may vary in different bituminous felts, and there are also bituminous felts described as ‘with SBS additive’, with worse properties and parameters than highly modified polymer-bituminous felts.
SBS plastomer
(atactic polypropylene) with the addition of saturated polyolefin elastomers, in addition to its stable form and good adhesion, provides resistance to acids and inorganic salts, ozone and high temperatures (up to 150°C). Bituminous felt, on the other hand, becomes quite stiff at sub-zero temperatures (-10)÷(-15)°C. APP-modified bituminous felts are difficult to combine with other types of bituminous felts, so this limitation must be taken into account when using them.
The role of the reinforcement in bituminous felts
The role of reinforcement is to provide the bituminous felt with mechanical strength and dimensional stability. The reinforcement is also a carrier for bitumen, so it must have high physical and chemical parameters and be resistant to biological corrosion. Therefore, bituminous felts on cardboard reinforcement are not a waterproofing material and should not be used as waterproofing.
The following types of bituminous felt can be distinguished:
bituminous felt on glass fabric reinforcement,
bituminous felt on glass fibre or plastic veil,
bituminous felt on non-woven polyester,
bituminous felt on non-woven polyester reinforced with glass fibre,
bituminous felt with an aluminium composite reinforcement, most often glass veil with aluminium (used mainly as a vapour barrier),
bituminous felt with copper insert (most often used on green roofs as a layer protecting against root penetration)
The glass fabric reinforcement has high tensile strength, but its disadvantage is low elasticity. A reinforcement made of non-woven polyester or polyester fabric is characterised by high tensile strength at break and high tear resistance. Non-woven polyester-glass material has high tear resistance to and thermal stability.
Weldable bituminous felt is usually manufactured on a glass fibre or polyester reinforcement, while self-adhesive membranes usually have a non-woven polyester, glass veil, glass veil with mesh, glass fabric or a so-called mixed reinforcement. Bituminous felts (unmodified) are usually manufactured on glass veil.
The characteristics of each type of reinforcement are given in the table below.
Reinforcement | Features and properties |
glass veil |
|
glass fabric |
Often used in the production of bituminous felt mechanically fastened to the substrate |
polyester |
Basic reinforcement (or reinforcement component) of weldable polymer-bituminous felts |
mixed with a predominance |
Glass fibres contribute to high dimensional stability while maintaining high flexibility provided by non-woven polyester |
mixed with a predominance |
|
Application in foundation waterproofing
When analysing moisture/water exposures and the structural layout of buildings and structures, certain typical areas of application for insulation can be identified:
horizontal under the foundation slab
vertical of foundation walls
horizontal under foundation walls (on strip footings)
floors on the ground
Bituminous felt insulation should always be installed on the side exposed to water or moisture pressure, i.e. on the outside of the building or protected element. Bituminous felt must not be allowed to peel away from the substrate unless a structural pressure layer is installed on top of the waterproofing.
Determining the essential characteristics of bituminous felts
In the context of these applications, it is worth noting that the standard specifies only two mandatory parameters: watertightness (20 cm water column for damp-proof insulation and 6 m water column for waterproof insulation) and straightness of edge. However, a whole range of other equally important parameters remain undefined. The standard does not impose their values or even their range – the manufacturer can declare them according to their own assumptions, while the designer decides independently which of the essential characteristics are key for a given application.
It therefore remains to define the required essential characteristics, i.e. the parameters of the waterproofing material used that are key to its service life (this is essentially a formal requirement, but one that is frequently disregarded).
Development directions and parameter modifications
Analysis of product parameters, properties and characteristics allows us to notice many significant differences, as well as the emergence of new features and properties of some products compared to others. For years, already at the stage of design, research and validation of this type of material, new technical properties and functional characteristics have been created, the aim of which is, among other things, to:
improve the application process – easier and faster work, reduction of the number of technological stages, shortening of breaks between successive phases;
expand the application possibilities of products – adapting materials to changing climatic conditions (e.g. high temperatures in summer, works in late autumn and winter), extending the construction season by enabling application at temperatures close to 0°C or below zero,
give them the widest possible versatility – one product instead of several previously used,
expand the range of their applications by introducing features and parameters beyond what is considered typical for a given product group,
add or expand functional features that are important during use, increasing the service life of the solutions.
A separate issue is the development of characteristics and parameters not only for individual products, but also the design of system solutions based on complementary and compatible materials.
All these activities are related to the development or expansion of the essential functional characteristics of products and their technical parameters, supported by research, numerous validation tests, experience gained in real-world applications, etc. They should be clearly distinguished from so-called ‘marketing communication’. The development of product features understood in this way is based on research, tests and the results obtained.
Waterproofing of garages and foundation slabs
Waterproofing of underground garages and buildings founded on a foundation slab is most often a case of moderate water exposure (described in the previous section, variant W2.1-E) or intense water exposure (variant W2.2-E). In addition, variant W3-E may occur, i.e. non-pressurising water exposure on buried suspended slabs (located in the ground) or even green roofs.
Waterproofing in variant W2.1-E
Let us analyse the waterproofing for variant W2.1-E (characterised by a water column pressure ≤ 3 m).
According to DIN SPEC 20000-202 [2], in such conditions it is recommended to use a waterproofing layer made of two layers of weldable polymer-bituminous felts, such as:
SBS-modified bituminous felt on mixed reinforcement (polyester-glass with a predominance of glass) with a minimum thickness of 4 mm,
APP-modified bituminous felt on mixed reinforcement (polyester-glass with a predominance of glass) with a minimum thickness of 4 mm,
SBS-modified bituminous felt on glass fabric reinforcement with a minimum weight of 200 g/m² and a minimum thickness of 4 mm.
Alternatively, it is possible to use a single-layer waterproofing made of weldable polymer-bituminous felt that meets the following requirements:
SBS-modified bituminous felt on polyester reinforcement with a minimum weight of 200 g/m² and a minimum thickness of 5 mm,
SBS-modified bituminous felt on mixed reinforcement (polyester-glass with a predominance of polyester) with a minimum thickness of 4 mm.
Waterproofing in variant W2.2-E
The situation is completely different when dealing with waterproofing for variant W2.2-E (characterised by, among other things, water column pressure > 3 m). In this case, the minimum number of bituminous felt layers is:
2 layers (including one on polyester reinforcement) for depths up to 9 m,
3 layers (including one on polyester reinforcement) for depths above 9 m.
The DIN SPEC 20000-202 standard [2] requires the use of waterproofing in such situations, e.g. weldable polymer-bituminous felt, such as:
SBS-modified bituminous felt on glass fabric reinforcement with a minimum weight of 200 g/m² and a minimum thickness of 4 mm
SBS-modified bituminous felt on mixed reinforcement (polyester-glass with a predominance of glass) with a minimum thickness of 4 mm
SBS-modified bituminous felt on a mixed reinforcement (polyester-glass with a predominance of polyester) with a minimum thickness of 4 mm
SBS-modified bituminous felt on polyester reinforcement with a minimum weight of 200 g/m² and a minimum thickness of 5 mm
Recommended NEXLER bituminous felts
From the NEXLER range, we recommend the following bituminous felts for such applications:
- PREMIUM PYE G200 S40 (thickness 3.8 ÷ 4.2 mm, flexibility -20°C, water resistance 200 kPa, linear and radial SBS modification, reinforcement weight 200 g/m²)
- PREMIUM PYE PV200 S40 (thickness 3.8 ÷ 4.2 mm, flexibility -25°C, water resistance 250 kPa, linear and radial SBS modification, reinforcement weight 200 g/m²)
- PREMIUM PYE PV250 S48 (thickness 4.6 ÷ 5.0 mm, flexibility -25°C, water resistance 400 kPa, linear and radial SBS modification, reinforcement weight 250 g/m²)
These bituminous felts (as well as others from the NEXLER range) are modified in a rather special way. The service life of the bituminous felt, and thus also of the waterproofing coating, depends largely on the quality and parameters of the material itself. For this reason, two types of complementary SBS modifiers are used. The first (so-called linear) is aimed at ensuring the flexibility of the finished product. The second (so-called radial) strengthens UV resistance (which is less important in the case of waterproofing in the ground) and resistance to ageing. The latter has a direct impact on the aforementioned service life.
The technology of profiling the underside of the bituminous felt shortens the welding time, which significantly affects the service life of the felt. This minimises the risk of damage (burning) to the material during application, provided that the flame is moved gradually, ensuring short-term action. The use of bituminous self-adhesive products or systems based on self-adhesive bituminous felts is also a good solution, as it contributes to increased durability and safety of use.
The actual essential characteristics of the above-mentioned bituminous felts significantly exceed the standard requirements. Flexibility (-20°C) ÷ (-25°C) at a tightness of 200 kPa ÷ 400 kPa (20 ÷ 40 m water column) is 330% to 660% higher than the standard requirements [1] for bituminous felts used as waterproof insulation. It is worth noting that the aforementioned materials (NEXLER PREMIUM PYE PV200 S40 and NEXLER PREMIUM PYE PV250 S48 bituminous felt) exceed the requirements of the DIN SPEC 20000-202 series standards [2] (Tables 2a and 2b), hence some of the longest (if not the longest) material guarantees for the bituminous felts.
| PARAMETER / PROPERTY | UNIT | VALUE |
| visual defects | - | none |
| straightforwardness | mm per 10 m | ≤ 20 |
| thickness | mm | MDV ≥ 4 (G) |
| watertightness | kPa | depends on the type |
| maximum tensile strength | N/50 mm | MDV > 1000 (G) |
| elongation at maximum tensile strength | % | MDV > 2 (G) |
| flexibility | °C | MLV ≤ -25 |
Table 2a: Selected technical properties of bituminous felts with glass fibre (G) and polyester (PV) reinforcement according to DIN SPEC 20000-202 [2]
Designations in Tables 2a and 2b (on the left and below):
- PYE – elastomeric bituminous felts (bitumen modified with thermoplastic elastomer (SBS))
- PYP – plastomeric bituminous felts (bitumen modified with thermoplastic plastomer (APP))
- KTG – mixed reinforcement with a predominance of glass
- KTP – mixed reinforcement with a predominance of polyester
- PV (number) – polyester reinforcement (weight in g/m²)
- G (number) – glass fabric reinforcement (weight in g/m²)
- S (number) – thickness of bituminous felt without sprinkle (mm)
- KSP – self-adhesive polymer-bituminous felts/membranes
- KSK – self-adhesive polymer-bituminous felts/membranes on an HDPE foil reinforcement
- MLV – specific limit value determined by the manufacturer, which must be achieved in tests
- MDV – specific value declared by the manufacturer, given with an assumed tolerance.
| TYPE OF BITUMINOUS FELT | REINFORCEMENT | MINIMUM CONTENT | TIGHTNESS |
bituminous felt on glass fibre or polyester fabric reinforcement (roofing)
| 200 g/m² | 1600 g/m² | 100 kPa/24 h |
weldable bituminous felt on glass fibre or
| 200 g/m² | - | 100 kPa/24 h |
weldable polymer-bituminous felt on glass fibre or
| 200 g/m² | - | 200 kPa/24 h |
self-adhesive polymer-bituminous felt (KSP)
| 200 g/m² | - | 200 kPa/24 h |
weldable polymer-bituminous felt on a mixed reinforcement
| 120 g/m² | - | 200 kPa/24 h |
polymer-bituminous felt (roofing)
| 200 g/m² | 2100 g/m² | 200 kPa/24 h |
| self-adhesive bituminous felt (KSK) on an HDPE reinforcement | HDPE 0.07 mm | - | 400 kPa/24 h |
Table 2b – selected technical properties of bituminous felts depending on composition
Service life and workmanship
The second factor that has a direct impact on the service life of waterproofing solutions is workmanship in accordance with current technical knowledge (part III).
______________________________________________
Bibliography
[1] PN-EN 13969:2006, PN-EN 13969:2006/A1:2007 Elastyczne wyroby wodochronne -- Wyroby asfaltowe do izolacji przeciwwilgociowej łącznie z wyrobami asfaltowymi do izolacji przeciwwodnej części podziemnych -- Definicje i właściwości
[2] DIN SPEC 20000-202 Anwendung von Bauprodukten in Bauwerken — Teil 202: Anwendungsnorm für Abdichtungsbahnen nach Europäischen Produktnormen zur Verwendung als Abdichtung von erdberührten Bauteilen, von Innenräumen und von Behältern und Becken
[3] Abc der Bitumenbahnen. Technische Regeln für die Planung und Ausführung von Abdichtungen mit Polymerbitumen- und Bitumenbahnen. Vdd Industrieverband Bitumen-Dach- und Dichtungsbahnen e.V., 2020
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.
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