Detailed explanation of the installation and construction details of expansion joints for waterproof backing boards

1、 Does the waterproof backing board need to have expansion joints

As an important building waterproofing material, whether expansion joints need to be left during the construction process of waterproof backing board depends on various factors:

1. Material characteristics: Most waterproof backing board materials (such as PVC, TPO, EPDM, etc.) themselves have certain thermal expansion and contraction properties. When the temperature changes significantly, the material will undergo noticeable dimensional changes, so expansion joints need to be left to adapt to these changes.

2. Structural requirements: The main structure of the building itself may deform due to temperature changes, load effects, and other factors. As a material attached to the main structure, the waterproof backing board must adapt to this deformation through expansion joints to avoid material damage caused by stress concentration.

3. Environmental factors: The setting of expansion joints is more important in areas with large temperature differences, direct sunlight, or large-scale installation. For continuous laying exceeding 6 meters in length, it is usually recommended to install expansion joints.

4. Construction specifications: According to relevant building waterproofing specifications, expansion joints must be installed on waterproof backing boards under specific conditions to ensure the long-term effectiveness of the waterproofing system.

Therefore, overall, in most application scenarios, waterproof backing boards require reasonable installation of expansion joints, which is an important measure to ensure the durability and functionality of the waterproof system.

2、 Construction details of expansion joints for waterproof backing board

1. Key points of expansion joint design

-Joint width determination: The width of expansion joints should be calculated and determined based on material properties, environmental temperature differences, and laying length, usually ranging from 20-50mm. For materials such as PVC and TPO, a ratio of 10mm joint width can be calculated for every 10 meters of length.

-Location selection: Expansion joints should be set at stress concentration points such as structural deformation joints, junctions of different materials, and corners of internal and external angles. For large-scale installation, it should be evenly spaced at intervals of 6-10 meters.

-Direction consideration: On sloping roofs, expansion joints should be set perpendicular to the drainage direction to avoid affecting the drainage function.

2. Preparation before construction

-Grassroots treatment: The grassroots must be flat, dry, sturdy, and free of sharp protrusions. At the expansion joint position, the base layer should be pre treated into a gentle transition slope or groove.

-Material preparation: Prepare specialized expansion joint cover plates, sealants, fasteners, and other supporting materials. These materials should be compatible with waterproof backing boards and have similar weather resistance.

-Line positioning: According to the design drawings, accurately mark the position of expansion joints on the base layer to ensure accurate positioning and straight lines.

3. Specific construction steps for expansion joints

(1) Standard expansion joint construction

1. Laying of backing board: Lay waterproof backing board according to the design requirements, reserve sufficient length when reaching the expansion joint position, and both ends should exceed the expansion joint position by at least 150mm.

2. Fixed end: Within the range of 150-200mm on both sides of the expansion joint, use dedicated pressure strips or mechanical fixing methods to fix the backing plate, and the fixing spacing should be appropriately increased.

3. Install the expansion device:

-For small expansion joints, the "Ω" - shaped or "Z" - shaped wrinkling method can be used, and the height of the wrinkling should be 1.5-2 times the width of the joint.

-For larger expansion joints, a dedicated expansion joint cover plate should be installed, with a width greater than the joint width and a minimum overlap length of 100mm on both sides.

4. Sealing treatment: Use specialized sealant to seal the edges of the expansion joint. The sealant should be continuous, uniform, of moderate thickness, and well bonded to the backing plate.

5. Additional layer treatment: Add an additional waterproof layer at the expansion joint position, with a width of not less than 300mm, and tightly overlap with the main waterproof layer.

(2) Special part expansion joint treatment

-At the corners of yin and yang: Radial expansion joints are set at the turning points of yin and yang corners, with the joint width appropriately increased and treated with a curved transition method.

-At the base of the through wall pipe: Install circular expansion joints around the pipe, with a width of 20-30mm, and fill them with elastic sealing material.

-Daughter wall base: Install a full-length expansion joint with a width of 30-50mm at the junction of the daughter wall and the roof, and fix it with metal pressure strips.

4. Key points of construction quality control

-Size control: The actual width of the expansion joint should not deviate from the design by more than ± 5mm, and the position deviation should not exceed ± 10mm.

-Fixed requirements: The distance between the fixed points on both sides of the expansion joint and the edge of the joint should be consistent, and the fixed spacing should not exceed 300mm. The corners should be appropriately densified.

-Sealing quality: The sealant should be full and continuous, without bubbles or cracks, and the bonding area with the backing plate should not be less than 90%.

-Appearance inspection: The expansion joint should be flat and smooth, without wrinkles or curled edges, and the cover plate should be installed firmly and overlapped tightly.

5. Common problems and preventive measures

1. Expansion joint leakage:

-Reason: Poor sealing, insufficient overlap of cover plates, and inadequate fixation

-Prevention: Strengthen sealing treatment, ensure overlapping length, and adopt dual waterproof measures

2. Bulging at the expansion joint:

-Reason: Improper fixation, obstructed thermal expansion and contraction

-Prevention: Adopt elastic fixation method and reserve sufficient expansion and contraction space

3. Cracking of sealant:

-Reason: Poor colloidal quality, improper construction temperature, and displacement exceeding the limit

-Prevention: Use high-quality sealant and apply it at a suitable temperature to ensure that the joint width is sufficient

4. Cover plate deformation:

-Reason: Insufficient material strength, excessive fixed spacing

-Prevention: Choose cover materials with sufficient strength and appropriately increase the number of fixing points

3、 Construction precautions

1. Environmental conditions: Expansion joint construction should be carried out at an ambient temperature of 5-35 ℃, avoiding working in rainy, snowy, and windy weather. Construction should be carried out in the morning and evening during the high temperature season.

2. Material protection: During the construction process, protective measures should be taken for waterproof backing boards and expansion joint fittings to avoid mechanical damage and pollution.

3. Process coordination: The construction of expansion joints should be coordinated and coordinated with adjacent processes to avoid damage to the expansion joints caused by subsequent operations.

4. Finished product protection: Clear signs should be set up after construction is completed, and personnel are prohibited from stepping on or stacking heavy objects before the waterproof layer acceptance.

5. Maintenance management: After the project is delivered, the status of expansion joints should be regularly checked, debris should be cleaned up in a timely manner, and any damage should be repaired in a timely manner.

4、 Conclusion

The correct setting and precise construction of expansion joints for waterproof backing boards are key factors in ensuring the long-term effectiveness of the waterproof system. Construction personnel should fully understand the working principle of expansion joints, strictly operate according to design requirements and construction specifications, pay attention to detail processing, in order to effectively prevent waterproof layer damage caused by factors such as temperature deformation and structural displacement. Meanwhile, selecting reliable supporting materials and scientific construction techniques are also important guarantees for ensuring the functionality of expansion joints. Through careful construction and standardized management, the waterproof backing board system can perform effectively, providing long-lasting and reliable waterproof protection for buildings.