I. Thoroughly treat the base layer to eliminate the "hotbed" of bubbles
The base layer is the foundation for membrane laying. Any unevenness, dirtiness, or dampness will cause air or moisture to remain, thereby forming bubbles.
Ensure the base layer is dry
The moisture content of the base layer must comply with specifications (usually ≤9%), which can be tested by the "film covering method": tightly cover 1㎡ of membrane (or plastic film) on the base layer, and after 24 hours, uncover it. If there is no condensation on the base layer and no moisture marks on the membrane, it is qualified.
Damp base layers must be treated: For concrete base layers, they can be ventilated and dried, or a base treatment agent (such as water-based sealing primer) can be applied to seal in moisture; for damp base surfaces (such as underground projects), suitable wet-laid membranes (such as cement-based permeable crystalline membranes) must be used, and forced laying should be avoided.
Ensure the base layer is flat and clean
The surface of the base layer must be polished flat to remove protrusions, edges, and loose particles (a 2m straightedge can be used for inspection, with a deviation ≤5mm). Cracks and pits must be filled with repair mortar (construction can proceed after drying) to avoid local lifting of the membrane.
Thoroughly clean the base layer to remove floating dust, sand particles, oil stains, release agents, and other debris (a high-pressure blower can be used for 吹扫). Otherwise, debris will isolate the membrane from the base layer, forming gaps.
Nodes such as internal and external corners and pipe roots must be made into rounded arcs (with a radius of over 50mm) to avoid hollowing caused by uneven stress on the membrane at right angles.
II. Strictly control materials to avoid "inherent defects"
Problems with material quality or compatibility will directly lead to adhesion failure and subsequent bubble formation.
Inspect membrane quality
Select membranes without wrinkles, damage, or holes, with tight cores (to avoid uneven edges caused by loose rolls). Ensure the membrane itself has no bubbles or delamination (check for bulges on the surface when unrolling the membrane).
For synthetic polymer membranes (such as PVC, TPO), check for pinholes and welding edge defects to prevent air from seeping through defects after laying.
Ensure material compatibility
Adhesives and base treatment agents must be compatible with the membrane material (for example, SBS modified bitumen membranes require bitumen-based adhesives, and polymer membranes require special matching adhesives). Mixing different types of adhesives is prohibited (for example, using bitumen adhesive to bond PVC membranes will cause hollowing due to insufficient adhesion).
Adhesives must be used within their shelf life and free from delamination, precipitation, or deterioration (for example, bitumen adhesives must be free of lumps after heating and melting, and water-based adhesives must be free of mildew).
III. Standardize construction operations to enforce "air exhaust and bubble prevention"
In the construction process, unexhausted air and insufficient adhesion are direct causes of bubbles. Operations must be refined for different laying methods:
Hot-melt method (e.g., SBS modified bitumen membranes)
Uniform heating to avoid "false adhesion": Use a spray gun to heat the bottom of the membrane and the surface of the base layer (focusing on the overlapping edges and central area of the membrane) to ensure the bitumen layer melts until it is "shiny and flowing" (temperature approximately 180-200℃). Avoid local unmelted areas (resulting in weak adhesion) or overheating (causing bitumen carbonization and failure).
Lay and press simultaneously for immediate air exhaust: When laying the membrane, one person heats with a spray gun, while another synchronously rolls with a heavy roller (over 50kg, with a rubber layer) from the middle of the membrane to both ends (or from low to high) at a uniform speed. The rolling speed should match the heating speed to ensure the melted bitumen fully fills the gaps in the base layer and squeezes out air (the roller must cover the entire width of the membrane to avoid missing any areas).
Focus on compacting overlapping joints: Overlapping edges need additional heating (temperature slightly higher than the main surface to ensure bitumen overflows). Use a small roller (10-15cm wide) to repeatedly roll the edges of the overlapping joints to avoid air retention at the overlaps.
Cold-adhesion method (e.g., self-adhesive polymer membranes, synthetic polymer membranes)
Apply adhesive "thin and evenly": Use a notched trowel to evenly apply adhesive (3-5mm thick), ensuring no missed application or accumulation on the base layer and the back of the membrane (for double-sided adhesive application). Accumulated areas, once cured, tend to form hard spots, leading to hollowing in surrounding areas.
"Dry the adhesive" sufficiently before bonding: After applying the adhesive, let it dry until it is "non-tacky to the touch" (approximately 10-30 minutes, adjusted according to temperature and humidity). Avoid bonding when not fully dried (solvents in the adhesive will not volatilize, forming bubbles) or over-dried (adhesive loses tackiness and fails to bond).
"Push and press to exhaust air from the inside out": When bonding, first fix the center of the membrane, then use a roller to roll diagonally from the center to both sides (or from bottom to top) at a slow and uniform speed to squeeze air out to the edges. If local bulging is found, immediately cut it open with a knife to exhaust air, reapply adhesive, and recompact.
Self-adhesive method (non-carcass self-adhesive membranes)
"Clean base layer + immediate compaction": When tearing off the membrane's release film, avoid touching the adhesive surface with fingers (oil will reduce tackiness). When laying, tear the film while immediately rolling with a roller (or scraper) (force ≥30kg) to ensure close bonding between the adhesive surface and the base layer, paying special attention to edges and corners (a rubber hammer can be used for tapping and compacting).
Avoid "laying with dust": If there is unremoved floating dust on the base layer, tearing off the release film will lift the dust, which will stick to the back of the membrane and form an "isolation layer" causing hollowing. Therefore, the base layer must be wiped again with a dry cloth before laying.
IV. Control the construction environment to reduce "external triggers"
Avoid adverse weather
Construction is prohibited on rainy or snowy days (damp base layers will cause moisture retention); during construction in winds above force 5, shielding is required (to prevent sand from sticking to the membrane or base layer, forming gaps).
When constructing in high temperatures (≥35℃), for the hot-melt method, reduce the heating temperature (to avoid bitumen flowing too quickly and causing bubbles); for the cold-adhesion method, shorten the adhesive drying time (to prevent the adhesive from drying too quickly and losing tackiness). In low temperatures (<5℃), suspend the cold-adhesion method (adhesive cures slowly with insufficient adhesion), and for the hot-melt method, increase heating intensity (to ensure sufficient bitumen melting).
Avoid damage from subsequent processes
Within 24 hours after membrane laying (before the adhesive is fully cured), prohibit people from walking on or stacking heavy objects on it to avoid membrane displacement and air entry. If subsequent construction is required (such as laying a protective layer), cover the membrane surface with a non-woven isolation layer to prevent hollowing caused by mechanical rolling.
V. Timely repair "budding bubbles"
If small bubbles (diameter <5mm) are found during construction, immediately inject the corresponding adhesive with a syringe and compact with a roller. For larger bubbles (diameter ≥5mm), cut them open in a cross shape, clean up internal debris, reapply adhesive, and patch with a membrane patch (edges extending over 50mm beyond the bubble) to ensure no gaps after repair.
Through the above measures, air and moisture retention can be reduced at the source, ensuring that the membrane is "airtight" with the base layer and between membrane layers, fundamentally avoiding bubble formation. The core principles are: the base layer should be "dry, clean, flat"; materials should be "matched, high-quality, fresh"; operations should be "uniform, compacted, exhaust air"; and the environment should be "stable, suitable, protected".
