Summary of common types of waterproofing projects and detailed treatment techniques

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This post was last edited by “Hasty Passerby” on September 16, 2018, at 14:58. A summary of common types of waterproofing works and detailed treatment techniques. Waterproof membranes are flexible building materials that can be rolled up; they are primarily used for building walls, roofs, as well as tunnels and highways. Their function is to prevent leakage of rainwater and groundwater. Acting as a leak-proof connection between the foundation and the structures, they serve as the first line of defense against water infiltration in any construction project, playing a crucial role in ensuring its overall waterproofing integrity. The main products are asphalt waterproof membranes and polymer waterproof membranes. This article provides a detailed introduction to the construction methods and precautions for waterproof membranes. http://img.civilcn.com/d/file/zhishi/sgjs/2018-08-01/5d0edba9b0008ee7200ac7230c216142.jpg 1. Requirements for the base surface: The base surface must be clean, with a moisture content of no more than 9%; it should be flat and compact, and all joints must be neat and complete, meeting the specified requirements. 2. First waterproof layer: (1) Lay a flexible waterproof layer; either coatings or membranes can be used. The construction requirements specify that the moisture content of the base surface should not exceed 9%, so it is suitable to carry out construction in summer, during hot weather after five consecutive days of clear skies. After completion, a water retention test should be conducted. (2) For coating-based waterproofing, taking “one layer of fabric and two coats of paint” as an example: after cleaning the base surface thoroughly, apply a coat of paint evenly; once it has dried and formed a film, lay a layer of glass fiber fabric as a reinforcing material, then apply another coat of paint evenly on the smoothed surface to secure it. After that dries, apply the next coat of paint. The total thickness of the waterproof coating should be over 3 millimeters. (3) For the installation of waterproof membranes, after cleaning the substrate thoroughly, apply adhesive to the back side of the membrane as well as to the substrate. Then, paste and roll the membrane from a distance towards the base, following the marked reference lines, and finally inspect and handle the seam ends. 3. Second waterproof layer: The rigid waterproof layer should be installed about two days after the completion of the first flexible waterproof layer. Its main materials include high-grade fatty acid-based mortar waterproofing agents, cement, sand, fine aggregate, and fibers; the thickness of this waterproof layer should be 20–30 millimeters. (1) Install the dividing strips in accordance with the specifications, with the division size set at 4000 millimeters × 4000 millimeters. Then sprinkle water to moisten the base surface, but there should be no standing water. (2) Apply the prepared mortar or fine aggregate concrete in sections, from far to near and from top to bottom; complete each section at once, then smooth and compact it. (3) After initial setting, remove the partition strips, smooth and trim the partition joints. (4) Use flexible sealing materials to fill the joint gaps and treat the surface joints. After construction is completed, pay attention to watering for curing. (5) If there is planting soil on the roof, it should be covered with that soil as soon as possible. http://img.civilcn.com/d/file/zhishi/sgjs/2018-08-01/f7e70462b87df11f907e0cc890a4bc5d.jpg 1. Roofing work is a sub-project of building construction; it refers to the construction of the roof surface layer, and includes tasks related to roof waterproofing as well as insulation. It consists of structural layers such as the roof leveling layer above the structural layer, the air barrier layer, the insulation layer, the waterproof layer, the protective layer, or the surface layer for use. The quality of its construction directly affects the service life of the building. II. Roofs can be classified by their shape into flat roofs, pitched roofs, and irregular-shaped roofs ； Based on their functional use, they can be divided into non-pedestrian roofs and pedestrian roofs ； Based on their insulation function, they can be divided into insulated roofs and non-insulated roofs. III. Roof waterproofing projects can be classified into rigid waterproof roofs and flexible waterproof roofs, depending on the properties of the waterproof materials used. A rigid waterproof roof refers to a roof that is made waterproof by using poured waterproof concrete, applied waterproof mortar, or by installing sintered flat tiles or cement flat tiles ； A flexible waterproof roof refers to a roof that is made waterproof by laying down waterproof membranes, asphalt shingles, or applying waterproof coatings. Depending on the type of waterproofing material used in their waterproof layers, roofs can be classified into rigid concrete waterproof roofs, flat tile roofs, membrane waterproof roofs, coating waterproof roofs, asphalt shingle waterproof roofs, metal sheet waterproof roofs, etc. http://img.civilcn.com/d/file/zhishi/sgjs/2018-08-01/a8e5fad4aea5503db582597c3f80b94c.jpg IV. Precautions for roof waterproofing construction: 1. It is strictly prohibited to carry out work on membranes and insulation during rainy days. 2. The leveling layer of the membrane waterproofing system must meet quality requirements and reach the specified level of dryness. 3. At joints such as roof corners, gutters, downspouts, ridges, membrane overlaps, and ends, the material must be laid carefully and tightly, compressed properly, with secure ends, in compliance with design requirements and relevant regulations set out in roof engineering technical specifications. Additional layers of membrane should be applied at roof corners, gutters, downspouts, ridges, and other such areas. 4. When laying the membrane, avoid over-tensioning and wrinkling; ensure proper venting between the substrate and the membrane, and after venting on both sides horizontally, use rollers to flatten and secure it in place. 5. The overlap width of the roofing material should be sufficient, and it must be laid smoothly; at the same time, construction must be carried out strictly in accordance with the markings provided on the substrate. 6. When installing the insulation layer, it is necessary to protect the waterproof layer well. The waterproofing work is an important aspect of building construction; the quality of this work affects the service life of the building and also has a direct impact on the normal progress of people’s economic activities and daily lives. According to statistics, there are several factors that cause roof leaks: materials account for 20%–22%, design accounts for 18%–26%, construction accounts for 45%–48%, and management and maintenance account for 6%–15%. Currently, there are many new materials available for roof waterproofing, but membrane waterproofing layers still hold an important position. Therefore, this article focuses on the construction of roof membrane waterproofing. http://img.civilcn.com/d/file/zhishi/sgjs/2018-08-01/dbe170fccb84f89b72e14c86f124e347.jpg The following tasks should be carried out before carrying out roof membrane waterproofing work. 1. Technical preparation before construction: Before starting roof construction, the construction unit should organize technical personnel to review the roof project drawings, understand the detailed constructions and relevant technical requirements specified in those drawings, and then develop a construction plan or technical measures for the roof project based on the actual conditions of the project. This prevents defects from arising after construction, which could lead to rework. At the same time, the work is carried out in an organized manner in accordance with the construction plan, thereby avoiding omissions, confusion, or disruptions that could affect the quality of the project. With the construction plan in place, the construction supervisor should next provide technical instructions to the work teams. The content includes: the areas to be constructed, the construction sequence, the construction techniques, the structural layers, the methods for strengthening key sections, the areas that need reinforcement and the corresponding methods, the quality standards for the project, the technical measures to ensure quality, the measures for protecting the finished products, and the safety precautions. II. Requirements for construction personnel and construction procedures: The waterproofing of roof projects must be carried out by specialized waterproofing teams or workers. It is strictly prohibited for units without the necessary qualification certificates, as well as non-specialized teams or workers, to carry out waterproofing work on roofs. The project owner or supervision company should carefully check the qualification certificates of the construction personnel. During construction, the contractor shall carry out self-inspections, self-evaluations, and self-corrections of quality in accordance with the construction procedures and stages, while keeping proper construction records. The supervision unit is responsible for verifying each stage of the work; only after approval can the next stage of construction proceed. III. Quality requirements for waterproof materials: The waterproof materials used in roof projects must come with proof of their quality, and they must be certified by an authorized quality inspection agency to ensure that their quality meets the requirements of the \"Technical Specifications for Roof Engineering\" (GB50207—94) or other relevant standards. After waterproofing materials arrive at the construction site, they should be accompanied by a factory inspection report and a certificate of conformity, indicating the date of production, batch number, specifications, and name. The construction unit shall take samples for re-inspection in accordance with the regulations. This sampling and re-inspection process is carried out strictly in line with the witnessed sampling and submission system: the construction workers take samples on-site under the supervision of a representative from the construction unit or personnel from the supervision unit, and these samples are then sent to the laboratory for testing. Only after passing the re-inspection and submitting the approval certificate for the re-inspection report can it be used in waterproofing projects. The use of substandard waterproofing materials in construction is strictly prohibited; any such substandard materials must be removed from the construction site immediately once they are detected. Key points for roof waterproofing construction: I. Environmental requirements for construction To ensure the quality of the construction work and the installation of the roofing membranes, it is advisable to carry out the work at temperatures between +50°C and +350°C ； Polymer-modified asphalt and high-molecular waterproof membranes should not be used in temperatures below zero; the hot-melting method for laying membranes allows construction at temperatures above -100°C. Such membranes are resistant to low temperatures and are not prone to damage when exposed to sub-zero conditions. Rain, snow, frost, fog, excessive atmospheric humidity, as well as strong winds are all conditions that make outdoor work inappropriate; otherwise, appropriate technical measures should be taken. II. Requirements for roof drainage slope: The drainage slope for flat roofs should be 2%–3%. When the slope is 2% or less, it is advisable to use materials to create a slope ； When the slope is greater than 3%, it is advisable to use structural grading. The longitudinal slope of gutters and eaves drains should not be less than 1%, and the drop at the bottom of the drain shall not exceed 200 mm. The slope within a radius of 500 mm around the water outlet should be no less than 5%. III. Treatment of voids and cracks in the roof base layer
The base layer consists of precast concrete slabs. When the gap between two adjacent slabs is less than 20 mm, it should be filled with fine aggregate concrete. The maximum size of the aggregates used should not exceed 10 mm, and the compressive strength of the concrete must be at least C20. Wherever possible, expansive cement or concrete mixed with an expansion agent should be used for filling the gaps ； When the gap width between the slabs is greater than 40 mm, 1ф6 rebar or rebar as specified in the design should be placed in that gap. After pouring the concrete for the gap, it should be covered promptly and kept moist for 7 days; construction can proceed only once the concrete reaches a strength grade of C15. Prevent the grout concrete from being subjected to construction loads too early, thereby ensuring the bonding strength between the slabs. When the base layer is cast-in-place reinforced concrete and cracks exist in the slab, first use a chisel to create grooves in those cracks that are 15–20 mm wide and shaped like an inverted V. Remove the debris from these grooves and clean them thoroughly. Then fill the cracks with sealant in two to three applications, allowing 15 minutes between each application. Once the cracks are filled, use a roller to smooth them out. IV. Requirements for the roof leveling layer: The leveling layer serves as the base on which the membrane waterproofing layer is applied; it provides a flat, dense, strong, and adhesive structural foundation for the waterproof membrane. Therefore, the leveling layer for laying the membrane must be solid; it should have no protruding sharp corners, depressions, or surface sanding. When checked with a 2-meter straightedge, the gap between the straightedge and the surface of the leveling layer should not exceed 5 mm. This gap may vary gradually, but there should be no more than one such gap per meter in length. The corners formed by the adjacent surfaces of the leveling layer should be made into arcs or obtuse angles. When the base layer is integral concrete, a cement mortar leveling layer is used with a thickness of 20 mm; the ratio of cement to mortar is 1:2.5 to 1:3 (by volume), and the cement grade must be at least 42.5. The leveling layer should also have division joints, which should be filled with sealing material; this helps to prevent or reduce cracking in the leveling layer. As a result, when the structure deforms or experiences temperature-induced changes, cracks will not form in the waterproof layer, thereby avoiding leaks. The joint width is 20 mm. The longitudinal and transverse spacing between expansion joints should not exceed 6 m. These joints are located at the supports of roof panels, at the junctions between the waterproof layer and protruding roof elements at roof corners, and at the junctions between the waterproof layer and parapet walls. It should also be aligned with the plate end seam, being even and straight. When applying the cement mortar leveling layer, first clear the roof slab of any debris and moisten it with water. When applying the mortar, proceed from far to near and from high to low. Apply it continuously within each grid section. Control the slope according to the design specifications. Use a screed bar longer than 2 meters to level the surface. After the mortar has partially set, use a trowel to compact and smooth it. Twelve hours later, cover it with straw mats and keep it moist through watering for curing. For detailed joints such as the roots of structures and pipes protruding from the roof surface, rounded arcs, frustums of cones, or frustums of pyramids should be formed using fine aggregate concrete; this prevents cracking or folding of the membrane at these joints and ensures proper adhesion. 1. Water outlet: It should be constructed within a 500-mm radius around it, with a slope of ≥5% and a smooth surface. 2. The bases of parapets, roof vents, and stairwell landings shall be made into arcs with a radius of 80 mm, constructed from fine aggregate concrete. 3. Extend around the base of the pipes protruding from the roof, and construct a frustum-shaped structure using fine aggregate concrete; the base of this frustum should be 300 mm wide and 60 mm high, with the surface to be leveled and smoothed. http://img.civilcn.com/d/file/zhishi/sgjs/2018-08-01/c35bcbbc5d8adbcf1046ef84188e517f.jpg V. Primer For the purpose of enhancing the adhesion between the waterproof membrane and the substrate and ensuring its integrity, a coating is applied to the substrate prior to the installation of the waterproof layer. Common primer treatments include cold primer and primers (base treatments) that are compatible with various polymer-modified bituminous membranes and synthetic polymer membranes. When selecting a primer, it must be compatible with the material of the membrane to prevent corrosion of the membrane or poor adhesion due to incompatibility, which could lead to delamination. Before spraying or applying the primer and base treatment agent, check that the leveling layer is dry and clean it thoroughly. Then, use a brush to treat areas such as roof joints, peripheries, and corners first; only after that can the application be carried out over a large area. The spraying or brushing should be thin and even; there should be no unpainted areas nor excessive thickness that causes peeling. The priming oil is applied 1 to 2 days before laying, and the membrane is laid only after about 4 days have passed since the substrate treatment agent has dried. VI. Laying of the membrane 1. Direction of membrane laying: The direction in which the membrane is laid should be determined based on the slope of the roof and whether there is any vibration on the roof. When the roof slope is less than 3%, the membrane should be laid parallel to the ridge ； When the roof slope is between 3% and 15%, the membranes can be laid parallel or perpendicular to the ridge ； When the roof slope exceeds 15% or when vibration is present, asphalt membranes should be laid perpendicular to the ridge; otherwise, laying them parallel or perpendicular to the ridge may be considered based on actual conditions. Lay them layer by layer from the eaves to the ridge; the various types of roofing membranes should overlap with each other, and the overlap points of multiple layers should be staggered. The upper and lower layers of membranes must not be laid vertically. 2. Sequence of membrane application: When applying the waterproof layer, it is necessary to first treat the joints, additional layers, and areas where roof drainage is concentrated (such as the junctions between the roof and downspouts, eaves, gutters, roof corners, and gaps at the ends of panels). Subsequently, the application should proceed from the lowest point on the roof upwards. When laying roofing membranes on gutters and eaves, it is advisable to do so in the direction of the gutter or eave edge to minimize overlaps. When laying roofs with multiple spans and varying heights, it should be done in the order of higher areas first, then lower areas; and farther areas first, then nearer areas. 3. Method and width of membrane overlapping: The membranes are laid using the overlapping method, and the overlapping joints between upper and lower layers as well as between adjacent membranes should be offset from each other. Joints parallel to the roof ridge should overlap in the direction of water flow; joints perpendicular to the roof ridge should overlap in line with the prevailing wind direction. At the junction of the gutter and the roof, the individual layers of the laminated membrane should be overlapped using a cross-over method, with the overlap seams spaced apart from each other ； Seams should be placed on the side of the roof or gutter, rather than at the bottom of the gutter. On arch-shaped roofs and slopes under skylights with a slope greater than 25%, short-side lapping should be avoided as much as possible; if lapping is necessary, measures must be taken at the joint to prevent the membrane from sliding down. VII. Detailed construction methods for waterproofing membranes: At the junction where the flashing meets the roof surface, the underlying surface should be shaped into an obtuse angle (>135°) or an arc (R=50–100 mm). The height to which the waterproof layer curls upward toward the vertical surface should not be less than 250 mm, with 300 mm being the common value. The joints of the waterproofing membrane must be sealed tightly to prevent water leakage at those areas. Waterproofing edges can take several forms, including free fall, overhanging edges, and gutters integrated within parapets. (8) Protection of roof waterproofing membranes: After the waterproofing membranes are installed, they must be properly protected to ensure that their waterproofing effectiveness is not compromised. On the waterproof layer, 300mm×300mm expanded perlite insulation blocks are laid, and above them a 3cm thick layer of cement mortar is applied as a protective layer. Steel wire mesh is placed within this layer, and joints are created in the protective layer; these joints are filled with sealing material to provide better protection for the waterproof layer. Precautions: To prevent the effects of water vapor from inside the building from causing bulging in the roof’s waterproofing layer, it is common practice in construction to install exhaust vents within the roof’s insulation layer and to add a vapor barrier on top of them (such as a layer of oil-paper, or one layer of felt with two layers of oil coating, or one layer of fabric with two layers of adhesive), in order to prevent water vapor from penetrating upward. The spacing between exhaust ducts should be 6 meters, arranged both horizontally and vertically; they must not be blocked, and should be connected to the exhaust vents that lead to the atmosphere. Before constructing the waterproof layer on the drainage roof, it is necessary to check whether the exhaust ducts are blocked and to clean and clear them if necessary. Creating a waterproof layer using roofing membranes is not a difficult task; as long as we follow the proper procedures for applying these membranes, ensure that each step is carried out carefully and to standard, we can prevent leaks in the roof caused by construction errors.