Construction Requirements for Cement Mortar Leveling Layer in Roofing Works
Release Time:
2020-08-24
Source:
Construction Requirements for Cement Mortar Leveling Layer in Roofing Works
1. Substrate Cleaning: Thoroughly sweep away loose debris from the structural layer and the insulation layer, and chisel and smooth any protruding hard lumps on the substrate surface.
2. When working on precast insulation panels, the panel bottoms shall first be firmly supported and leveled. For vertical joints and corner areas that are difficult to fill, it is recommended to compact and level these areas using crushed fragments of the same type of insulation panel.
3. Watering and Moistening: Prior to applying the leveling layer, the base layer should be moistened; however, it must not be saturated with water. The degree of moisture should be carefully controlled to ensure strong adhesion between the leveling layer and the insulation layer.
4. The substrate that does not readily bond with the leveling material shall be surface-treated to improve adhesion.
5. Expansion joints shall be provided in the leveling layer, with a typical joint width of 20 mm. The joints shall be located at the ends of the slabs, and the maximum spacing between longitudinal and transverse joints shall be as follows: for cement-sand or fine aggregate concrete leveling layers, no more than 6 mm; for asphalt-sand leveling layers, no more than 4 mm. The joints shall be filled with sealing material.
6. The drainage slope of the leveling layer shall comply with design requirements. For flat roofs, the material-based slope should be 2%; for roof gutters and eaves troughs, the longitudinal slope shall not be less than 1%, and the elevation difference at the bottom of the gutter shall not exceed 200 mm.
7. At the junctions between the insulation layer (base layer) and protruding roof structures (parapets, gable wall expansion joints, vent openings, etc.), as well as at internal corners of the base layer, the leveling layer shall be formed into rounded arcs with radii conforming to the requirements specified in the following table. Around the internal drainage outlet, the leveling layer shall be constructed as a slightly depressed pit.
8. Gutters, corners, and base details shall be completed prior to large-area plastering; areas with slope requirements must comply with drainage specifications.
9. For large-area plastering, spread the mortar between the two screed laths, smooth it out with a trowel, then use a screed board to level it according to the elevation marks on the laths on both sides. Next, use a wooden float to further smooth the surface, and finally check the flatness with a wooden straightedge.
10. Troweling the second and third passes with a steel trowel: When the cement mortar begins to set—such that footprints remain upon stepping on it but no sinking occurs—perform the second troweling pass, taking care to avoid any areas that are left untroweled and smoothing out any depressions, dead corners, or sand holes. Once no trowel marks can be produced, proceed to level and compact the surface, completing the third troweling pass. This step should be carried out before the mortar reaches final set. The consistency of the mortar should be maintained at approximately 70 mm.
11. Curing: After the leveling layer has been smoothed and compacted, it shall be watered for curing at ambient temperature 24 hours after completion; the curing period shall generally be no less than 7 days. Waterproofing work may be carried out once the surface has dried.
