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Selection of waterproof materials Source: Internet. Choosing the right waterproof materials is an important aspect of waterproof design, and it plays a decisive role. Today, there is a wide variety of materials, with different shapes and properties, as well as significant differences in price ； The construction methods vary. Therefore, the selected materials must meet the requirements of the project: engineering geology and hydrology, structural type, construction season, local climate, building usage functions, as well as specific requirements for special areas – all of which impose particular demands on waterproofing materials. I. Selection of Materials Based on Climate Conditions 1. China has a vast territory, with significant temperature differences between the north and the south. In the Jiangnan region, summer temperatures can exceed 40 degrees Celsius and persist for several days; the waterproof layer on rooftops, being exposed to such intense sunlight, loses its waterproofing properties prematurely. The materials selected should have strong resistance to ultraviolet rays and a high softening point, such as APP-modified asphalt membranes, EPDM membranes, and PVC membranes. 2. It is rainy in the south, snowy in the north, and arid in the west. There are about 15 provinces, municipalities, and autonomous regions with an annual rainfall of over 1000 mm. With 200 days of continuous rain, the rooftops remain wet all the time; poor drainage leads to water accumulation that does not dry up for months, soaking the waterproof layer. Coatings with poor water resistance are prone to re-emulsification or hydrolytic reduction reactions ； Adhesives that are not resistant to water bubbles significantly reduce the bonding strength, causing the polymer membranes in the bonded joints to crack; this is especially true for gutters with internal drainage systems, where leaks occur due to prolonged exposure to water. To this end, water-resistant materials should be used, such as modified asphalt sheets with glass fiber or polyester mats, or water-resistant adhesives for bonding polymer sheets. 3. In the arid and rain-scarce northwestern regions, evaporation is much greater than precipitation, and often there is no water left on the eaves after it rains. Clearly, the level of water resistance in these areas is reduced; for secondary buildings, having a basic level of protection is sufficient to meet the water resistance requirements, and with an appropriate protective layer in place, a long service life can be achieved. 4. In extremely cold and snowy regions, some waterproof materials cannot withstand the cyclic changes caused by freezing and thawing, resulting in premature aging and failure. Four or five months of the year are covered by thick layers of snow; the snowmelt water continuously soaks the waterproof layer, and as the snow melts and then freezes again, adhesives that lack frost resistance and poor water resistance will fail. In these areas, SBS-modified asphalt membranes or polymer membranes with welded seams are recommended. If waterproof materials that are not resistant to low temperatures are used, the roof should be constructed in an inverted configuration. 5. The season for waterproofing work cannot be ignored either. It is also very cold in North China; water-soluble coatings cannot be used, and adhesives lose their bonding properties at 5°C, making it impossible to carry out construction work at temperatures below zero. The design was done in summer, but construction took place during the coldest periods of the year; the adhesive froze when it came into contact with concrete and lost its adhesive properties. The seams of the rolled material fail to stick together, resulting in failed construction, project delays, and additional costs for materials and fees. In the summer in the northeast, waterproof materials that are sensitive to cold can be used for construction, but during the harsh winters, these completed waterproof layers cannot withstand the effects of freezing and thawing, and deteriorate prematurely. When designing, it is important to understand the appropriate temperature range for the selected materials. II. Different building components require different waterproofing materials, as the materials used in various building parts vary. Each material has its own advantages and disadvantages; no single material can be used for everything. There is no material that is suitable for all applications. Different materials can only complement each other, not replace one another, as each has its own appropriate use. Roof waterproofing and basement waterproofing require different material properties, while bathroom waterproofing and wall waterproofing differ even more. Sloped roofs, roofs with complex shapes, and roofs with metal sheet substrates also present distinct requirements, so careful consideration must be given when selecting materials. 1. The roof waterproofing layer is exposed to the elements: it is subjected to the scorching sunlight, strong winds, erosion from rain and snow, extreme temperatures in both cold and heat, as well as repeated expansion and contraction due to day-night temperature differences. Without high-quality materials and proper protective measures, it is difficult for such a layer to achieve the required durability. Therefore, waterproof materials with high tensile strength, high elongation, and good aging resistance should be chosen. Such as polyester mat polymer-modified asphalt sheets, EPDM sheets, P-type PVC sheets (with welded seams), and one-component polyurethane coatings (with a protective layer). Various roof designs will be discussed in more detail later. 2. The reason for wall leaks is that walls are too thin nowadays; they are often built using lightweight blocks, with numerous gaps both on the inside and outside. Additionally, the joints where doors and windows meet the walls are not properly sealed, allowing rainwater to seep in through those gaps. For wall waterproofing, membranes cannot be used; only coatings can be employed, and they must be combined with exterior finishing materials. The gaps in window frame installation can only be resolved with sealant. 3. Material selection for waterproofing in underground structures. The underground waterproof layer is exposed to water or highly moist soil throughout the year, so the waterproof material must have excellent water resistance. Rolls made from perishable rubber compounds cannot be used; the waterproof layer on the bottom surface should be made of thick waterproof material with a certain resistance to punctures. It is best for the layer to be 6mm-8mm thick. If synthetic polymer sheets are used, heat welding the joints is the most suitable method. For those who use adhesives to seal joints, the adhesive must have excellent water resistance; otherwise, no matter how good the roofing material is, it cannot be used. Waterproof coatings should be used with caution. When used alone, the thickness is 2.5 mm; when combined with coil material, the thickness should also be 2 mm. 4. The waterproofing of bathrooms has three characteristics. First, it is not affected by natural climate conditions; there are no temperature fluctuations, and thus low requirements are placed on the elongation rate of the materials ； Second, it has a small area, many right angles, and numerous pipes running through the floor slabs ； Third, tiles are installed on the wall waterproof layer, showing good affinity with the adhesive. Based on these three characteristics, coil materials cannot be used; coatings are the most suitable option. Among coatings, cement-based acrylate coatings are the best choice, as they allow tiles to be firmly attached to them. 5. For the waterproofing of roofs installed in landfills, lakes, ponds, and ditches, polyethylene geomembranes are the best choice; they should have a width of over 5 meters, welded seams, and good puncture resistance. 6. With an increasing number of overpass projects in urban construction, reinforced concrete beams and slabs must be waterproofed to extend their service life. Since a high-temperature asphalt concrete pavement is laid on the waterproof layer, the waterproof layer must be able to withstand temperatures of 110°C. Use APP confessional asphalt coating or APP modified asphalt rolls. 7. The waterproofing technology for cave warehouses is complex, as there are rock caves and loess caves. In rock caves, there are two types of lining: wall-separated lining and wall-attached lining. Rock-lined lining for Dongting Lake. After spraying concrete, a cement mortar leveling layer is applied on its surface, followed by the installation of polymer-modified asphalt sheets or polyethylene geotextile membranes; PVC waterproof membranes can also be used. For rock caverns with wall-type lining, a waterproof coating, polyurethane coating, or neoprene latex asphalt coating is sprayed on the surface of the shotcrete. Loess caves are often lined with blocks for internal waterproofing. Apply polymer waterproof mortar on the surface of the cement mortar or paint it with an acrylate coating. III. Material selection requirements based on engineering conditions 1. The building classification is the primary factor in determining the materials to be used; for buildings of grade 1 and 2, high-quality waterproof materials must be employed, such as polymer-modified bitumen membranes with polyester backing, synthetic polymer membranes, and composite synthetic polymer coatings. For buildings of grade III and IV, the range of available materials is broader, and they will not be listed one by one here. 2. Tiles for sloped roofs. For clay tiles, asphalt shingle tiles, concrete tiles, metal tiles, wooden tiles, slate tiles, and bamboo tiles, a separate flexible waterproof layer must be placed beneath them. Since fixed nails pass through the waterproof layer, it is required that the waterproof layer have the ability to hold these nails, in order to prevent rainwater from seeping in along the nails into the cladding. The most suitable membrane is a 4mm thick polymer-modified asphalt membrane. Polymer sheets and coatings are both unsuitable. 3. Roofs with significant vibration, such as those located near railways or in earthquake-prone areas, those with cranes or hammers inside factories, and large-span lightweight roof trusses. Vibrations are intense, causing the mortar base to crack easily, and the fully adhered membrane gets torn apart. Coils or coatings with high elongation and high strength should be selected, such as EPDM coils, polymer-modified asphalt coils with polyester mats, and PVC coils, and they should be laid by spreading or spot-adhering during the day. 4. Roofs with steep slopes that are not accessible to people cannot be used, as the slope angle can be very high, exceeding 60°. It is not possible to apply a solid protective layer over the waterproofing layer; therefore, only membranes containing mineral fillers should be used, or membranes covered with aluminum foil or metal sheets. IV. Material selection based on architectural functional requirements 1. The roof is used for landscaping to beautify the urban environment. Planting soil is spread over the waterproof layer to grow flowers and plants. Plant roots have strong penetrating force; therefore, in addition to being resistant to corrosion and immersion, the waterproof layer must also have resistance to penetration. Polyethylene geomembrane (welded seams), polyvinyl chloride sheets (welded seams), lead-tin alloy sheets, and root-resistant modified asphalt sheets are used. 2. The roof area can be used for recreational activities and industrial purposes, such as dance halls, small ball games courts, tea houses, drying areas, observation decks, etc. A block protective layer should be laid on top of the waterproof layer. The waterproofing material does not need to be fully bonded. The elongation requirement for the coating material is not high; various types of coatings can be used, and it can also be employed for composite waterproofing that combines rigidity and flexibility. 3. The inverted roof design features the insulation layer on top and the waterproof layer below. The insulation layer protects the waterproof layer from sunlight, as well as from the effects of heavy rain, strong winds, extreme cold, and scorching heat. There is a wide range of waterproof materials available, but careful and meticulous construction is essential to ensure no leaks over the material’s service life. If a leak occurs, it is difficult to repair it; often, it is necessary to remove the insulation layer and the *layer, which leads to difficulties and waste. 4. The water storage surface is very similar to a pool, except that the water depth is shallow, generally not exceeding 25 cm. Since the waterproof layer is submerged in water throughout the year, the waterproof material must have good water resistance. Polyurethane coatings, silicone rubber coatings, Fullsheng polymer sheets (heat-welded seams), polyethylene geomembranes, and lead-tin metal sheets can be used; sheets that cannot be bonded with adhesives should not be utilized. V. Points to consider when selecting materials 1. Evaluation of good and poor quality materials: If good materials are used, leaks may occur after one year ； It uses secondary materials, and there has been no leakage in eight years – so which is better, the primary or the secondary materials? What criteria should be used for evaluation? There are four criteria for evaluating the quality of materials: first, the material should have good physical properties, such as high tensile strength, good elongation at break, resistance to high temperatures and low temperatures, water impermeability, and aging resistance; it should also be easy to work with, offering advantages over materials of the same type. We say this is good material. Second, it has good waterproofing performance for a certain part of the building. Different types of waterproof materials have different uses. No single material can handle everything. Rolling materials are excellent for covering large areas of roofs, but they are not effective for waterproofing bathrooms and walls; coatings are much more suitable for such purposes. Surfaces with a small area and many irregularities are ideal for coatings. Another example is rigid concrete waterproofing, which is most suitable for basement walls and floors. Using rigid waterproofing for large-span roofs is not only impossible but also indicates an unreasonable design. Third, fully utilize the unique properties of the materials. Materials such as high-density polyethylene geotextiles have high resistance to puncture and crushing, but poor flexibility; they are suitable for use on green roofs and even better for landfills. However, they are not suitable for roofs with complex shapes. Select materials that take advantage of their strengths while avoiding their weaknesses; those that leverage their advantages are good materials. 2. Rigid waterproofing is considered permanent, but in reality it is not reliable. For many years, some people have believed that concrete’s natural waterproofing properties are permanent, that it is cost-effective, and suitable for waterproofing basements, roofs, as well as bathrooms – seemingly suitable for every application and capable of replacing other waterproofing materials. This is a one-sided exaggeration of the self-waterproofing capabilities, ignoring the negative aspects; in fact, rigid self-waterproofing has many weaknesses that are difficult to overcome. (1) Both naturally mined sand and gravel, as well as sand and gravel that have been artificially crushed, find it difficult to meet the desired gradation requirements, and thus fail to achieve an ideal impermeability curve. (2) It is difficult to achieve a uniform and accurate gradation of sand, gravel, cement, and water. The ratio of ash to sand is high, there is less sand, and more cement is used; as a result, the concrete shrinks significantly and cracks form. Conversely, if there is too much sand and too little cement, the cement cannot cover all the sand; the mixture becomes dry and lacks cohesion, resulting in insufficient density of the concrete. (3) The mud content in sand and gravel is often too high, exceeding 2% of the required level. (4) There is an improper understanding of the use of admixtures; adding an appropriate amount of water reducer can be very effective, but there is often a preference for expansion agents. The expansion agent is effective in the early stage, but cracks increase later on. (5) Proper curing is crucial for concrete, but it often isn’t done properly. (6) Uneven vibration during construction, over-vibration, and missed vibrations occur from time to time; visibly visible honeycombing and pitting are not unusual, but it is the invisible forms of honeycombing and pitting that are more common. (7) The rebar in concrete hinders the movement of aggregates, affecting compactness. (8) Concrete exposed to the natural environment, subjected to sunlight, freezing, snow, and rain, experiences rapid changes in drying shrinkage, which leads to cracks in the concrete. (9) Concrete is not a permanently fixed solid; it undergoes creep and carbonation, thereby **reducing its durability**. (10) Concrete is itself a porous material, and it is impossible for it to be impermeable to water. Water that seeps into the pores reacts with calcium hydroxide in the concrete along with carbon dioxide from the atmosphere to form electrolyte solutions such as calcium carbonate. During the early stages of construction or at later times, when electric current comes into contact with this mixture, the rebar corrodes and expands, causing the concrete to crack and peel away. In short, the idea of self-waterproofing reinforced concrete is good, but the success rate is low, and many difficulties are hard to overcome. Try to avoid using concrete rigid waterproof roofs. 3. Advantages and disadvantages of rolled materials: Half a century of practice has shown that rolled materials have more advantages, as evidenced by the large volume in which they are used. The thickness of the rolled material remains consistent; it is manufactured in factories with very small errors. As a result, the thickness stays the same regardless of the location where it is applied, and it is not affected by the levelness of the substrate. The installation of this rolled material is fast and efficient – one work team can handle 30–50 m2 per day on average. The membrane can be laid without any support, unaffected by the moisture level of the substrate, which reduces the construction time. Using a loose lay method can prevent the waterproof layer from being torn apart by cracks in the base layer. Using rolled materials for waterproofing vertical walls is very convenient, with simple installation. Rolls are easy to transport, saving labor and effort. The coil material has a long storage life and will not deteriorate due to being unused for months. However, the width of the rolls is usually one meter; during installation they are joined together, with a seam every meter, and can be made into one unit through heat melting or welding. If the adhesive seams are used, there is a drawback, as this represents a fundamental weakness. Even if the installation is done meticulously, the adhesive itself does not have a long lifespan. The sheeting is still new, but the adhesive has deteriorated. EPDM rubber sheets are of excellent quality; their lifespan is estimated to be around 40 years. Some EPDM sheets provide a very strong initial adhesion, but over time their bond weakens and they separate from each other. Multiple open flanges mean that no matter how good the material is, it won’t help. A single layer of adhesive is not sufficient; it is necessary to follow the foreign practice of using both adhesive and multiple layers of sealant for joint sealing. 4. The flexible waterproof layer should have sufficient thickness. An adequate thickness of the waterproof layer is an important condition for extending its service life. (1) Extended the old age period. The waterproof layer is exposed to wind, rain, sunlight, and freezing in winter every day, causing its surface to age. The aging process progresses from the surface inward, layer by layer. Although it is slow, over time the entire thin waterproof layer ages. Therefore, increasing the thickness of the waterproof layer extends its lifespan. (2) It is beneficial for preventing cracks at the base level. If the waterproof layer is fully bonded to the substrate, cracks in the substrate will stretch the waterproof layer. Materials with a thin waterproof layer are not easy to peel away when under tension and tend to break; whereas thicker waterproof materials can still stretch in the upper part even if there are cracks on their lower surface. (3) It helps to resist unintentional damage by people. Even after the waterproofing layer was completed, people continued to walk on it, push carts, move items around, and stack things there. Thin waterproof layers are easily damaged, while thicker ones can withstand some impacts and abrasion. (4) The base layer should be flat and clean, but it often cannot be swept thoroughly, leaving behind gravel. If the waterproof layer is thin, it can be easily punctured, while a thicker waterproof layer can withstand such damage.