Causes of seven common quality problems in roofing work and preventive measures

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Causes of seven common quality problems in roof engineering and preventive measures. Roof engineering is an important sub-project of construction projects, and as a key aspect reflecting the quality of such projects, it is particularly crucial to address common quality issues. The following examples summarize seven common quality issues in roofing projects, analyze their causes, and propose preventive measures; everyone should pay close attention to these in such projects. Question 01: Examples of sanding, peeling, and cracking of the leveling layer
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Severe sanding of the leveling layer
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Cracking of the leveling layer
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Cracking of the leveling layer
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Poor repair results for the leveling layer
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Analysis of the reasons for improper construction of the leveling layer: 1) The mix ratio and preparation of the cement mortar used for the leveling layer do not meet the design requirements. 2) The subbase was not properly prepared before the cement mortar was laid. 3) Imperfect construction during the paving and compaction of cement mortar. 4) No timely maintenance was carried out after construction. Control measures: 1) The mix ratio of the cement mortar leveling layer should meet the design requirements; a volume mix ratio of 1:3 for cement mortar should be used, with a water-cement ratio of less than 0.55. 2) Cement mortar should be mixed mechanically, with strict control over the water-cement ratio; the mixing time should be no less than 1.5 minutes, and it should be used immediately after mixing. 3) Before paving the cement mortar, the base layer should be cleaned thoroughly and fully moistened with water ； During paving, pure cement slurry should be applied, and cement mortar should be laid promptly. 4) When paving and compacting the cement mortar, use a straightedge to level it, and a wooden trowel for rubbing and pressing; then, before it starts to set and lose moisture, use an iron trowel to compact and smooth it in two stages. 5) After construction, it should be covered promptly with plastic film or straw mats and watered for curing to keep its surface moist; the curing period shall be no less than 7 days. Issue 02: Examples of roof membrane cracking http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/d57747c700d814e50e50f46bcc958237.jpg Cracking of the membrane occurs due to the overheating of the additional layer, which affects its waterproofing capabilities. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/29d05c03eaab12390404f6d8416f693a.jpg Method of installation: Start from the lower part of the slope, working from farther areas towards the nearer ones; ensure that the long axis of the membrane is perpendicular to the slope direction, with the overlaps aligned in the direction of water flow ； The upper and lower layers of membrane shall not be laid perpendicular to each other; the second layer must be offset by 1/2 of its width from the first layer. Reasons: 1) Inadequate consideration in the design. 2) Poor material properties of the coil. 3) Poor construction techniques. 4) When a cement mortar leveling layer is used for the insulation roof, the stiffness of the base layer is insufficient. 5) Poor protection of finished products. Control measures 1) Improve design and structure. 2) Use qualified coil materials. 3) Improve the rolling material laying and bonding process. 4) A concrete or reinforced concrete leveling layer is recommended for use on the insulation layer. 5) Enhance the awareness of protecting finished products. Issue 03: Examples of roof leaks http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/39330bf6e96fb4cdb7508e5c11ec8de8.jpg Leaks occur because no additional layer is installed at the outlets of pipes on the roof. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/95335b05e58c777ec10e4f2c1445d9e9.jpg Improper installation of roofing membranes, with the width of the additional layer in both horizontal and vertical directions being less than 250 mm. Reasons for this: 1) Insufficient thickness of the insulation layer; inaccurate mixing ratio of the cement mortar used for the leveling layer, resulting in insufficient strength; poor finishing of the leveling layer, as well as inadequate curing, leading to issues such as a loose surface, sanding, and peeling. 2) The leveling layer shall not have grids, nor shall there be ventilation channels or vents. 3) The roof slope is gentle, especially at the base of the parapet, in the gutters, and at the drainage outlets. 4) The chimneys, pipes, access holes on the roof stand out; there are issues with the curvature at joints, at areas with different heights, and at the base of the parapet wall. The height of the flashing is insufficient, and the sealing of the waterproofing membranes is poor. 5) For some sections of the parapets and at areas with different heights, the old method of using overhanging eaves and flashings is still employed. 6) The thickness of the roof waterproofing layer is insufficient. Prevention and control measures 1) The raw materials used shall meet the **specified standards and construction code requirements. 2) The thickness of the insulation layer must meet the design requirements; if no such requirements are specified in the design, the thinnest part of the insulation layer (at the parapet wall and at the drainage outlets) must not be less than 100 mm. Pre-fabricated cement perlite blocks should be used, and the use of perlite produced on-site is not allowed. 3) When using cement mortar for the leveling layer, it is essential to strictly control the amount of cement used; the ratio of cement to sand should not exceed 1:3. The leveling layer must be compacted and smoothed in a timely manner, and proper curing measures should be taken. During curing, humidity control is necessary. When applying the leveling layer, partition joints should be created, with a width of 20 mm. The width of the ventilation channels between these joints should be 30–40 mm. These ventilation channels should be arranged at intervals of 6 meters both horizontally and vertically, interconnected with each other, and connected to exhaust pipes that lead to the outside atmosphere. The exhaust pipes should be made of D75 mm metal tubes, with waterproof caps on top. When laying the waterproof layer, additional layers should be installed in the ventilation channels. 4) When applying the leveling layer, it is essential to strictly control the drainage slope direction and gradient; the gradient should be no less than 2%, and the drainage outlet must be significantly lower than the surrounding area. 5) Highlight the access hatches, chimneys, pipes, expansion joints, and variations in roof height on the roof; the base of the parapet wall must have a concave curve, with no right angles allowed. The height of the flashing shall not be less than 250 mm. The waterproof material must be embedded in the groove to ensure a secure seal. When the wall is made of concrete, metal strips can be used to fix it in place. When plastering the groove, 1–2 layers of plaster should be applied first, so that it matches the finish of the parapet wall; the plastering should reach the same level as the bottom of the groove. It is not advisable to plaster the parapet wall first and then fill the groove, as this could lead to the formation of horizontal cracks. The height of the waterproof material at the pipe root at the prominent level should not be less than 250 mm. The sealing area must be secured with metal straps. Joints for deformation include expansion joints, settlement joints, and seismic joints; the methods for dealing with these joints are essentially the same. Before decoration, it is necessary to thoroughly clean any debris from within these joints. After cleaning, the joints should be filled with foam plastic or asphalt hemp, and then covered with waterproof material. A concrete cover or metal cover should be placed on top; the metal cover should have interlocking edges, and sufficient space should be left to allow for deformation compensation, taking into account the size of the joints. 6) In accordance with the specifications, the old practice of having an overhang of 6 cm should no longer be used. On roofs accessible to people or on roofs with rigid waterproofing, gaps should be left at the junctions with gables, parapets, and other structures that protrude from the roof, and these gaps should be sealed using flexible sealing materials. 7) The bonding material for waterproof membranes shall have a thickness of not less than 1 mm per layer, and the thickness of the surface layer shall be not less than 2 mm. 8) Before the completion of the project, a 24-hour water retention test must be conducted on the roof to check for any leaks. The results of this test must be signed and sealed by the persons in charge of water management from both parties (as well as the supervision staff), and then included in the completion documents for archiving. Issue 04: Incorrect slope grading leading to poor drainage. Example: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/83836d564990da71604fc6d9aa2281a3.jpg. Incorrect slope grading on the roof results in poor drainage. Example: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/7dcc68d65fe46fb6b74f2ad73e070d10.jpg. Poor drainage on the roof causes water accumulation. Example: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/5468465a42296aa84e1299991f2b53aa.jpg. The slope within a radius of 500 mm around the water outlet should be no less than 5%. Reason for this: 1) The slope gradient of the roof’s drainage system does not meet the required standards. 2) The drainage slope in the gutter and eaves gutter is not up to standard. 3) The inner diameter of the downspout is small, and debris such as roof waste and fallen leaves has not been removed. Prevention and control measures 1) Properly handle the relationship between water separation, drainage, and waterproofing in the design. 2) The slope of the roof and drainage channels must meet the standard requirements. 3) During the construction of the roof leveling layer, strings should be used strictly in accordance with the designed slope, and reference points (guiding strips) should be set at the corresponding locations. 4) Clean up garbage and fallen leaves on the roof in a timely manner. Question 05: Examples of damage to membranes after installation http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/ea5b779590ad718dca4f8a8d3491c9e8.jpg Damage to membranes after installation http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/99e5852f2259c2e17951b2085a362bf9.jpg Analysis of the reasons for damage to membranes after installation: 1) The substrate was not cleaned properly. 2) Workers should operate while wearing shoes with nails. 3) Construct brick piers or brick ridge walls directly on the sheet material. 4) Direct dumping of mortar, concrete, etc. Prevention and control measures: 1) The membrane waterproofing layer should be cleaned multiple times before construction. 2) Workers must wear soft-soled shoes while working. 3) The carts used to transport materials should be covered with soft rubber or burlap. 4) When constructing brick piers, etc., a sheet of membrane should be placed under the pier, and the bricks should be laid evenly. Construction materials should be handled with care to prevent damage to the waterproof membrane. Question 06: Examples of bulging in membranes after installation http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/a41ef032a352d6f06240f1b2efb5d75a.jpg Inconsistent application of the primer can lead to poor adhesion of the membrane, which in turn causes it to bulge. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/c6329a277313318841191df6d8a9ed7f.jpg Moisture in the substrate can also cause the membrane to bulge. Analysis of the reasons: In areas where the membrane is not properly bonded within the waterproofing layer, moisture and gas accumulate; when exposed to sunlight or artificial heat sources, these substances expand and cause bubbling. Prevention and control measures: 1) The leveling layer should be flat, clean, and dry, with the base treatment agent applied evenly. 2) Raw materials should be protected from moisture intrusion. 3) Before construction, clean the surface of the membrane thoroughly. 4) Construction shall not be carried out in rainy, foggy, windy, or dusty conditions to prevent the base layer from getting wet. Question 07: Examples of parapet wall leaks http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-15/837d3df1204ff5ddf56c0b2a7b439774.jpg Analysis of the reasons for improper waterproofing at the parapet wall: 1) There is no gap between the roof structure layer and the parapet wall. 2) Uneven settlement of the foundation. 3) Poor design and low construction quality. 4) Temperature differential drying shrinkage cracks in cement mortar plastering. Control measures: 1) Poor foundations should be reinforced. 2) Reduce the impact of constraints. 3) Improve the waterproofing treatment of detailed structures. 4) Important buildings should have reinforced concrete parapets. 5) Different construction measures should be adopted in different regions.