Water in liquid or in vapour form

Transcription

1 Waterproofing With Cementitious Slurries By Dr. Hermann Lutz, Wacker Polymer Systems Water in liquid or in vapour form is the most destructive weathering element for building constructions, like concrete, masonry, and natural stone structures. Waterproofing and damp-proofing techniques have to preserve a structure s integrity, functionality and usefulness throughout its whole life time. To prevent all possible water intrusion causes, the exterior (side) of a building must be protected form top to bottom with waterproof materials. All waterproof measures have to be part of a whole system and must interact integrally for complete effectiveness and to prevent water infiltration. Should one of these systems (parts) fail or not act integrally with all other protection systems, leakage will occur. Adequately controlling groundwater, rainwater and surface water, as well as the transport of humidity in form of water vapour will avoid unnecessary repairs to building exterior or its damage or even destruction (deterioration). Apart form protecting the exterior of building constructions, there are a multiplicity of waterproofing materials for interior use, as for bath rooms, toilets, swimming pools, water tanks, etc. Some of the waterproofing measures are used to protect against the detrimental action of aggressive substances like salts and acids transported by the water. Waterproofing Systems The different components of a building s exterior can be classified in: Roofing: has to prevent as an external layer water intrusion in horizontal or slightly inclined directions. Below-grade waterproofing: materials and measures that prevent surface and ground water or water under hydrostatic pressure from entering into a structure or its components. These systems usually are not exposed or subjected to weathering such as by ultraviolet radiation. Examples for belowgrade waterproofing materials are metal and plastic films, cementitious waterproofing sealing and bituminous waterproofing systems (materials). Above-grade waterproofing: a combination of materials or systems that prevent water intrusion into exposed structure elements, including protective decorative barrier systems. These materials are not subjected to hydrostatic pressure but are exposed to weathering and pollutant attack. Examples for abovegrade waterproofing are all kinds of paints including cementitious paints, mineral finish plasters and renders if they are in accordance with the Künzel s rule, which requires an extremely low coefficient of water absorption (water repellent effect), combined with a sufficiently high water vapour permeability (requirement: coefficient of water absorption W < 0,5kg/ m 2 h; and water-vapour diffusion equivalent air-layer thickness S d < 2 m; and S d x W < 0,2 kg/m2 h). Damp-proofing: materials which reduce or prevent water vapour transmission and which are resistant to water vapour or minor amounts of moisture; these systems may act as backup systems to primary water-proofing materials. Damp- proofing materials are not subject to weathering or water pressure. Flashing: materials or systems installed to direct water entering through the building skin back to the exterior. Flashings are installed as backup systems for waterproofing or dampproofing systems. Traditional sealing and waterproofing systems, e.g. according to the German standard DIN 18195, include bituminous materials, plastic waterproofing foils and metal tapes for interior and exterior applications. In order to seal and to protect the surface of buildings and structural components against the action of dampness and water, in addition to this traditional systems nowadays products based on reactive resins (e.g. epoxy or polyurethane resins), purely dispersionbound paste-form products (so-called paintable waterproofing membranes) and mineral waterproofing (cementitious waterproofing membranes) are widely used. In the following the cementitious waterproofing and their application will be discussed. Cementitious waterproofing Cementitious waterproofing membranes have been successfully used for more than 40 years in Europe for protection of a wide range of building structures and structural components either exposed periodic or long-term wetting (surface water, seepage water), low hydrostatic pressure (soil dampness) or in combination with 72

2 appropriate engineering even high hydrostatic pressure. Cementitious membranes () are used for waterproofing wet rooms and water tanks, and due to their excellent weathering resistance for exterior surface protection as well. Typical applications are the sealing and waterproofing of e.g. basement walls, water tanks, swimming pools, walls and floors in wet-rooms like toilets and bathrooms, balconies and terraces (as a waterproofing layer to be tiled over). In addition flexible cementitious waterproofing membranes are often used as a protective surface-coating system for structural concrete (e.g. protection of reinforced structural concrete for new structures as well as for concrete structures after rehabilitation; protection against penetration of water, chlorides and free carbon dioxide in order to avoid corrosion of the reinforcement) or as a protective layer for building constructions against aggressive chemicals (sulphates, acids, e.g. in waste-water drains). Advantages of cement-based waterproofing are their excellent resistance against water, even if exposed permanently, their excellent resistance against long term weathering, a good scratch resistance, a good load-carrying capacity and a much higher water vapour permeability compared to most of the other systems (consequently no problems with blistering when water vapour permeates through the waterproofing membrane). Cement based waterproofing are easy to use, are non-toxic, they provide a fully bound and monolithic surface without joints, they can easily be applied on substrates with complex surface shapes. In contrary to other systems, cementitious waterproofing can be applied even on damp and wet mineral surfaces and their physical properties are less temperature-dependent compared to bitumen based materials. Pure and simple cement-based are still used for the protection against surface water, but they are not suitable to seal against water under hydrostatic pressure. In order to improve the poor adhesion, the poor water tightness, and the extremely low deformability or flexibility of pure cementitious, polymers are added in form of liquid dispersions on job-site or in form of a redispersible powder already mixed in the dry-mix mortar. The use of special additives in the dry-mix mortars like water retention agents, thickening agents and rheological additives in combination with the polymeric binder in form of the Vinnapas Redispersible Powder, provide an excellent workability and make sure that there is no need for a post water-treatment of the applied slurry. Today different systems of cementitious waterproofing membranes or are available: Standard or rigid mineral waterproofing Standard, rigid mineral waterproofing are polymer-modified prepacked dry-mix mortars which are mixed (gauged) with water before being applied as a slurry by brush, roller or airless spraying, as well as by trowel if less gauging water is used. Standard or rigid waterproofing can only be used for mineral substrates which are stable, sound and solid, and if there is no risk for crack formation, movements or dimensional changes (e.g. shrinkage). A typical composition for such a rigid membrane is given in Table 1, some typical characteristics in Table 2. The water tightness depends on the cement content, the shape and particle size distribution of the fillers, the type of chemical additives used and the amount 73

3 of polymer in form of Vinnapas Redispersible Powder. Redispersible powders are used as polymer binders in order to improve the adhesion of the slurry on different substrates, to improve its cohesion, the flexibility, the abrasion resistance and toughness and last but not least the water tightness and density of the mortar. Such polymer modified cementitious waterproofing can withstand the water pressure not only form the positive side, but to a limited extend, due to their excellent adhesion and cohesion, in addition form the negative side, too, if this is necessary for some special practical applications. Preferentially, a redispersible powder with a hydrophobic (water repellent) effect like Vinnapas RI 551 Z is incorporated in the dry-mix mortar. Typical dosage is 2 to 10%, depending on the quality of the raw materials available, the formulation and the requirements in respect of the water tightness and mechanical characteristics. If tightness against hydrostatic pressure is required, higher amounts of polymer in form of a Vinnapas Redispersible Powder have to be used (5 to 10%). It is important to know, that the use of water repellent agents will provide to a cementitious mortar waterrepellent or waterproofing characteristics, but does not make the mortar impermeable against water under hydrostatic pressure. In order to achieve this, the mortar must be very dense (appropriate filler particle size distribution) with a low air-pore content and a sufficient high polymer content (the polymer has to close the cavities and pores). Flexible cementitious waterproofing (two-component systems Developments in the late 1970s have led in Europe, in addition to the traditional rigid waterproofing, also to flexible waterproofing which to a limited extent are capable of bridging over small cracks (up to approx. 1 mm) in the substrate. The flexibility of such products strongly depends on the polymer/cement ratio and, to a lower extent, on the flexibility of the polymer itself. In addition the flexibility of a cementitious waterproofing membrane depends after application and during its life-time upon the environmental conditions it is being exposed to. These conditions can be simulated by laboratory test methods, using different storage conditions. When a flexible cementitious slurry is applied and stored under dry conditions, especially at high temperatures and on absorbant substrates, only a minor part of the cement of this thin-layer system is able to react. Therefore the actual effective polymer/cement ratio is higher than the theoretical value and thus the whole system is very flexible, being dominated by the polymer binder. When later the cement has rehydrated under humid or wet conditions, the system will achieve his final strength, with the consequences that the tensile strength will increase, and the elongation and so the flexibility will decrease. Therefore, the mechanical characteristics of cementitious membranes can only be compared, if the cement used in the formulation is fully hydrated. This means, that cementitious have to be tested in the laboratories under conditions providing a full hydration of the cement in order to check the remaining flexibility after long water immersion. This is important to avoid failures due to insufficient flexibility after the complete hydration of the cement in practice. Flexible waterproofing cementitious are used on substrates being supposed to shrinkage, vibrations, movements, stresses, crack formation and on substrates difficult to be coated like wood, steel, aerated light weight blocks and gypsum. Due to their high polymer content, they are diffusion and chemically resistant against chloride, sulphate ions and carbon dioxide and other aggressive materials. Two-component flexible cementitious waterproofing can be offered in two different types of product forms: (a) as a two-pack system composed of a prepacked dry-mix mortar based on cement, fillers and other additives plus a liquid dispersion in the second pack. The dry-mix mortar is mixed on jobsite with the diluted aqueous dispersion which contains preservatives and some other additives. This is the mostly used system nowadays for two-component flexible waterproofing membranes. In most cases the dry-mix mortar already contains a minimum of polymer in form of a Vinnapas Redispersible Powder. (b) as a system based on a wet premix (aqueous dispersion), fillers and additives. This paste-form product is blended on job-site with the locally available Portland cement, giving a flexible waterproofing slurry, depending on the dosage and quality of the cement. A typical composition for such a rigid membrane is given in table 1, typical characteristics in Table 2. In most cases aqueous styrene-acrylic dispersions with a Tg between 0 and 40 C are used as a liquid component. One-component flexible cementitious The disadvantage of two-component systems for their practical application is the occurrence of mixing errors due to the lack of knowledge, experience and education of the workers concerning the appropriate dosage of the liquid component. Wrong doses may also happen by chance or even intentionally in order to save money in the short term. Using too low dosages of the liquid dispersion, the resulting membrane may loose its waterproofing capability if exposed to hydrostatic pressure or will at least provide a reduced flexibility with failure of the system as a consequence. Other reasons for not using two-pack systems, apart from the difficult and risky handling, are the expense and logistics difficulties (e.g. the need for additional containers and the problem of their safe disposal; storage and transport of liquid dispersions which could freeze or deteriorate through microbiological attack) and more time consuming and harder work on the job-site when handling two-pack systems). Because of these many disadvantages of modifying mortars with liquid dispersions, today more and more the socalled one-component flexible cementitious in form of a premixed dry-mix mortar are used. Wacker Polymer Systems developed special Vinnapas Redispersible Powders with a very low Tg, a low water absorption and a high water resistance in order to be able to formulate onecomponent flexible cementitious 74

4 waterproofing sealing. The technical performance for this products is comparable with two-component cementitious waterproofing as shown in Table 2. The higher costs for such a product, due to the high dosage of the redispersible powder, is compensated by the advantages having a one-component premixed polymer-modified dry-mix mortar, like e.g. low-cost logistics and packaging, safety and reliability for the application by exclusion of mixing errors on job-site, higher productivity on job-site. Paintable, ready-to-use dispersion-bound waterproofing membranes Ready-to-use (paste-form) dispersionbound waterproofing membranes provide an extremely high and longlasting flexibility and very good adhesion on all inorganic and organic substrates. These products are mainly used, besides the flexible cementitious, if very flexible waterproofing membranes are demanded and for substrates with poor adhesive characteristics (e.g. on bituminous substrates, on gypsum substrates, on plywood). These membranes have a relatively low cohesion and show some softening after prolonged water immersion with a certain risk of blistering. Forming an impermeable film by physical drying, these products are not suitable to be applied under high humidity conditions. Such products are not suitable for exterior and floor applications and cannot be used for applications with permanent water immersion. In addition there are disadvantages concerning the logistics with liquid or paste-form products like risk of bacterial growth, transport of water and expensive packaging. Installation and application of cementitious waterproofing membranes Before applying cementitious systems, the substrates must be free of dirt, laitance, release agents, and other foreign materials. The substrate must be sound and solid, all tie holes honeycomb, and cracks must be filled with appropriate cement mortars. When using flexible waterproofing cementitious, construction joints, wall-to-wall and wall-to floor joints must not be sealed, for these joints an elastic sealant (e.g. silicone sealant) or embedded elastic plastic foils have to be used. Cementitious waterproofing membranes can be applied by brush, roller, trowel or by an airless spraying machine. Mostly a brush is used to apply a slurry-like mortar, for this reason these products are very often called cementitious waterproofing. All cementitious waterproofing sealing or membranes have to be applied in a such a way that after drying a layer with a thickness of at least 2 mm will result. This is generally obtained only with multiple coating, mostly with two or three coats (typical drying time is 2 to 5 hours before application of the second layer). In order to assure the imperviousness of the membrane, at least 2 coats have to be applied in order to seal pores and micro cracks which may have been formed or left within the first coat, even if a layer of 2 mm or more could be applied in one step e.g. by trowelling the slurry at 3 mm thickness. It is not necessary to keep the freshly applied polymer modified slurry moist or to post-treat it with water, but it is important to ensure that it can dry slowly. Exposure to rain or excessive sunshine must be avoided in the first few hours, or, even better, for the first day. For areas where permanent hydrostatic pressure is anticipated, the application of the adequate waterproofing slurry must be done at the positive side of the structure to be waterproofed. If waterproofing membranes should be used for drinking water tanks, local restrictions about the use of polymer modified mortars in contact with drinking water have to be respected. Technical requirements and performance of waterproofing Typical compositions for different classes of cementitious waterproofing are given in Table 1. 76

5 Table 1: Typical composition of cementitious waterproofing Type of waterproofing slurry A B C D Portland cement or special cement Filler (silica sand, special lamellar fillers, carbonates) compl. to compl. to compl. to compl. to 100% 100% 100% 100% Thickening agents (organic and mineral like bentonites) Water retention agents (e.g. cellulose ether) 0 0,1 0,2 0,2 0,2 Defoaming agent 0 0,5 0,5-1 0,5 1 0,5 1 Vinnapas Redispersible Powder Vinnapas Dispersion (50% polymer) A = simple, rigid cementitious waterproofing slurry with no resistance against hydrostatic pressure B = rigid standard waterproofing slurry resistant against hydrostatic pressure C = two-component flexible waterproofing slurry resistant against hydrostatic pressure D = one-component flexible waterproofing slurry resistant against hydrostatic pressure Technical requirements for waterproofing membranes (e.g. concerning flexural strength, compressive strength, tensile strength, elongation at break, water vapour permeability, crack overbridging capability, water-uptake, impermeability under hydrostatic pressure, adhesion on the substrate) are defined, based on more than 40 years of practical experience in Europe, together with the guidelines for the application for this type of products in the technical rules and recommendations of the Deutsche Bauchemie (formerly IBH). Table 2 Type of waterproofing slurry A B C D Flexural strength [N/mm 2 ], after 28 d sc * * Compressive strength [/mm 2 ], after 28 d sc * * Shrinkage [mm/m], after 28 d sc with 16x4x4 cm prisms * * Tensile adhesion strength [N/mm 2 ] on concrete slab as a 2 mm layer 28 d sc 0,5 1,0 1,0 1,5 1,0 2,0 1,0 2,0 7 d sc + 21 d in water 0,5 1,0 1,0 1,5 0,5 1,0 0,5 1,0 28 d sc + 14 d 70 C + 1 d sc 0 0,5 1,0 2,0 1,0 2,5 1,0 2,5 7 d sc + 21 d in water + 25 cycles freeze/thaw 0 1,0 1,0 1,5 1,0 1,5 1,0 1,5 Tensile test with 2 mm film at 23 C, after storage 28 d sc (EN 196) Elongation at break [%] * * Tensile strength at break [N/mm 2 ] * * 0,5 2,0 0,5 2,5 Capillary water absorption [kg/m 2. h], DIN > 2 0,2-2 0,05 0,5 0,1 0,5 Water vapour permeability Sd [m], DIN ,05 0,4 0,05 0, Water impermeability test; no water penetration for 14 days under a hydrostatic pressure of [bar], IBH guidelines Crack-overbridging properties [mm], IHB guidelines 0 0 0,5 1,5 0,5 1,5 * not to be determined due to low strength or low flexibility If multiple layer systems are used in order to waterproof a construction structure, the modulus of elasticity of each coating should be lower or at least not higher than the modulus of the layer below it, in order to prevent crack formation and failure of the system. Vinnapas is the commercial name for thermoplastic polymer binding agents of Wacker Polymer Systems. In combination with mineral binders (mainly cement Vinnapas Redispersible Powders are used in the construction industry with great success for more than 45 years. Typical applications for polymer modified dry-mix mortars are: ceramic tile adhesives and building adhesives, jointing and grouting mortars, thermal insulation adhesives and base-coat mortars, self levelling mortars and screeds, concrete repair mortars and mortars for concrete rehabilitation systems, all types of plasters, renders and mineral finishing coats, lime-cement paints and cement-free powder paints, sealing, joint fillers, trowelling and smoothing compounds. Very simple products such as masonry mortars, thicklayer screeds and base-coat plasters or renders are usually not modified with Vinnapas Redispersible Powders. Vinnapas Redispersible Powders are polymer binding agents that are produced by a spray drying process of special water based polymer dispersions. Dispersion powders were invented in 1958 by Wacker Chemie, and today Wacker Polymer Systems is the world-wide market leader for redispersible powders. The polymer modification of dry-mix mortars with Vinnapas Redispersible Powders will, depending on the dosage, improve: the water retention and the workability of the fresh mortar, the adhesion on all substrates, the flexibility and deformability of the mortar, it s flexural strength and abrasion resistance, it s toughness, cohesive strength and density (impermeability). In addition, special Vinnapas Redispersible Powders can confer a hydrophobing effect making the mortar strongly water repellent. MBJ 77