I. Core Influencing Factors: Keys to Determining "Feasibility of Construction"
1. Climatic Conditions (Most Critical Factor)
Climate directly affects the drying/curing speed and film-forming quality of the coating. Focus on four dimensions: temperature, humidity, precipitation, and wind speed:
Temperature: 5°C to 35°C is the optimal range
Most waterproof coatings (e.g., water-based acrylic, polyurethane, JS composite coatings) rely on moisture/solvent evaporation or chemical reactions to form films. Temperatures that are too low (<5°C) can cause:
Water-based coatings to freeze easily, damaging the emulsion structure and leading to cracking or chalking after curing.
Reaction-type coatings (e.g., two-component polyurethane) to cure extremely slowly or even stop reacting, resulting in sticky, low-strength coatings.
Temperatures that are too high (>35°C) can cause:
Rapid moisture evaporation in water-based coatings, leading to quick surface skinning while internal moisture remains trapped-this causes blistering or pinholes later.
Fast solvent evaporation in solvent-based coatings, resulting in shrinkage cracks in the coating.
Special Note: Some low-temperature-specific waterproof coatings (e.g., modified bituminous waterproof coatings) can be applied at 0°C to 5°C, but the product manual must be confirmed in advance. Additionally, thermal insulation measures (e.g., covering with geotextiles) are required after construction.
Humidity: Relative humidity < 85% with no condensation
High-humidity environments prolong the coating's drying time. If humidity in the substrate or air exceeds limits (e.g., plum rain season, post-rain periods):
Water-based coatings struggle to dehydrate and cure, remaining "tacky" and failing to form an effective waterproof film.
Solvent-based coatings are less affected by humidity, but high humidity may cause condensation on the substrate surface, reducing adhesion between the coating and substrate and leading to peeling later.
Judgment Method: Wipe the substrate with a dry cloth. If the cloth stays dry and no moisture returns to the substrate surface within 1 hour, construction is feasible. Alternatively, use a hygrometer to ensure relative humidity meets requirements.
Precipitation: No rain/snow within 24 hours before and after construction
Rain during construction: Uncured coatings will be washed away by rain, causing uneven thickness, missed areas, or complete failure.
Rain within 24 hours after construction: The coating will not have fully formed a film yet, and rainwater will seep into the coating, disrupting the curing reaction and creating "false waterproofing."
Recommendation: Check the weather forecast for the next 24–48 hours before construction, avoiding rainy or overcast days (continuous sunny days are optimal). If light rain occurs suddenly during construction, immediately cover the constructed area with plastic sheeting. After rain, let the substrate dry completely (for at least 24 hours), then inspect the coating for damage before reapplying.
**Wind Speed: Wind speed < Level 5 (light wind or calm)**
Excessively high wind speed (>Level 5) can cause:
Rapid evaporation of moisture/solvent on the coating surface, leading to "surface drying while internal layers remain wet" and subsequent cracking.
Dust and debris to adhere to the uncured coating, affecting waterproof sealing and appearance.
2. Substrate Condition (Foundation for Determining Waterproofing Lifespan)
The substrate must meet four requirements: dry, flat, clean, and firm. Otherwise, even with suitable climate conditions, the coating will fail:
Dryness: Substrate moisture content ≤ 8% (roofs/walls), ≤ 10% (basements)
Moist substrates create a "water film" between the coating and substrate, drastically reducing adhesion and causing blistering or peeling later.
Testing Method: Cover the substrate with a 1㎡ plastic film, seal the edges, and leave it for 24 hours. If no condensation forms inside the film and the substrate remains dry, it is qualified.
Flatness: Substrate surface deviation ≤ 2mm/2m
Protrusions, cracks, or honeycomb-like defects cause uneven coating thickness (excessively thick layers in depressions crack easily; overly thin layers in protrusions leak easily). Repair uneven areas with cement mortar in advance, and reinforce cracks with anti-crack mortar or non-woven fabric.
Cleanliness: No dust, oil, or laitance
Dust on the substrate surface reduces coating adhesion, while oil damages the coating emulsion structure. Sweep the surface with a broom, wipe with a damp cloth, and clean oil-stained areas with diluted dish soap before drying.
II. Recommended Optimal Construction Times for Different Scenarios
1. Roof Waterproofing Construction
Seasonal Selection: Spring and autumn (April–May, September–October) are optimal
Roof surfaces can reach over 60°C in summer, causing coatings to cure too quickly. Winter temperatures are low and may cause freezing, making film formation difficult. Spring and autumn offer moderate temperatures (15°C–25°C), low humidity, and minimal precipitation-ideal for slow, uniform coating curing.
Time of Day: 9:00–11:00 a.m. and 14:00–16:00 p.m.
Avoid midday high temperatures (12:00–14:00) and early-morning dew (6:00–8:00) to prevent surface skinning or dew damage to the coating.
2. Basement/Underground Garage Waterproofing Construction
Seasonal Selection: Avoid the plum rain season (June–July in southern China) and low-temperature winter periods
Basements inherently have high humidity, and the plum rain season exacerbates moisture buildup. Choose dry, rain-free seasons (e.g., April–May, October–November in northern China; March, October in southern China). Ensure good ventilation in the basement (e.g., turn on exhaust fans to reduce humidity).
Time of Day: Construction is feasible throughout the day (if ventilation is poor, morning construction is recommended to leverage daytime temperature rises for faster drying). Ensure no standing water or water seepage in the basement during construction and curing (usually 24–48 hours).
3. Bathroom/Kitchen Waterproofing Construction
Phase Selection: After plumbing/electrical renovations and before tile installation (once the substrate is completely dry)
Bathroom substrates undergo "plumbing trench cutting → backfilling → leveling." Backfill layers (e.g., ceramsite) must dry thoroughly (usually 7–10 days of ventilation and air-drying), as excessive substrate moisture causes coating blistering.
Climatic Selection: Avoid rainy or high-humidity days. If indoor humidity is high, use a bathroom heater (warm air mode) or fan to accelerate substrate drying.
III. Key Precautions Before, During, and After Construction
1. Before Construction
Carefully read the product manual to confirm the coating's optimal application temperature and humidity (requirements may vary by brand and type, e.g., one-component vs. two-component polyurethane).
Conduct a small-area test coating: Apply a small patch of coating to an inconspicuous part of the substrate, observe it for 24 hours, and proceed with large-area construction only if the film forms evenly with no cracking and strong adhesion.
2. During Construction
Control coating intervals: Most waterproof coatings require 2–3 coats. Apply the next coat only after the previous one is completely dry and cured (no stickiness or indentation when touched lightly). Intervals typically range from 6–12 hours (extend if temperatures are low).
3. After Construction
Finished product protection: Avoid foot traffic or debris stacking during the curing period (usually 2–3 days) to prevent coating damage.
Water tightness test: After the coating is fully cured (3–7 days, per product manual requirements), conduct a 24–48 hour water tightness test. Proceed with subsequent processes (e.g., tile installation) only if no leakage is confirmed.
In summary, the core principle for selecting the optimal construction time for waterproof coatings is to prioritize ensuring "suitable temperature and humidity + dry substrate," then avoid extreme weather based on specific scenarios (roof/basement/bathroom). Ultimately, standardized construction ensures effective waterproofing.
