What issues should be paid attention to during the application of cement-based waterproof coatings?
Release Time:
2015-08-27
Source:
What issues should be paid attention to during the application of cement-based waterproof coatings?
Cement What issues should be paid attention to during the application of waterproof coating?
I. Construction Key Points
1. Substrate Preparation
(1) The base surface must be solid and clean. Areas with obvious cracks (generally defined as cracks wider than 0.2 mm) must be repaired. Leakage points must be properly sealed to prevent water infiltration.
(2) Any substances on the substrate surface that impede penetration, such as oil stains, release agents, latex paint, and oil-based paint, must be thoroughly removed.
(3) Sprinkle water over the mortar and concrete substrate on the construction surface to thoroughly moisten it, ensuring no standing water remains.
2. Ingredients
(1) Mix proportions: During construction, the water-to-cement ratio must be strictly controlled. For brushing, mix powder and water at a weight ratio of 1:0.35–0.4; for troweling and applying, mix powder and water at a weight ratio of 1:0.3–0.35, ensuring thorough and uniform mixing. Mechanical mixing is recommended to ensure complete dissolution of the active ingredients.
(2) Within the specified water addition range, apply a slightly higher water content for horizontal surfaces and a lower water content for vertical or sloped surfaces to prevent the material from flowing.
(3) Do not prepare excessive quantities at one time; it is best to use the mixture within about 20 minutes. During application, if the paint thickens, add an appropriate amount of water to adjust its consistency and continue using it. However, if the paint has hardened, it must no longer be used.
3. Painting
(1) Prior to application, the base surface of mortar and concrete must be thoroughly wetted.
(2) Application may be carried out using a roller, scraper, or brush, with two coats required; the amount of material used for each coat may be the same. The second coat may be applied once the first coat has surface-dried and cured. Prior to applying the second coat, water should be sprinkled to keep the first coat moist but free of standing water. Each coat should be applied in as consistent a direction as possible, with uniform thickness, and care should be taken to avoid any areas being missed. The direction of the second coat should be perpendicular to that of the first.
(3) For dry-sprinkling application, the concrete shall be thoroughly vibrated and compacted during placement, and any surface bleed water shall be removed before commencing the dry-sprinkling operation while the concrete is still in its initial set but not yet fully dry. During application, the waterproof coating must be evenly sprayed, and at the same time, a trowel shall be used to firmly and smoothly finish and smooth the coating.
II. Post-Construction Maintenance
1. Curing in the later stage is of great importance. Sprinkler curing may be initiated immediately after the coating has reached initial set. Under normal conditions, spray the surface three times daily for 2–3 consecutive days, ensuring that the coating remains thoroughly moist with each application. On hot or dry days, increase the frequency of spraying; if necessary, cover the coated surface with straw bags or plastic film for additional protection. Of course, the ideal practice is to keep the coating continuously moist throughout the entire curing period.
2. During the curing period, the coating must be protected from rain, direct sunlight, and frost for 48 hours after application.
3. The duration of curing shall be determined based on actual conditions. For concrete structures that contain liquids (such as water tanks, swimming pools, and reservoirs), a curing period of 7 to 14 days is mandatory; for basements and foundations, the curing period shall not be less than 7 days.
III. Precautions
1. Do not add cement, quartz sand, or other materials to the waterproof coating, nor incorporate any admixtures that have not been approved through testing; otherwise, the coating’s penetration-crystallization-based impermeability performance will be compromised.
2. When preparing the waterproof coating, dilute it as much as possible within the allowable water-to-material ratio; this facilitates the penetration of the coating’s active ingredients into the base mortar.
3. Prior to construction, the substrate mortar concrete must be brought to a fully saturated, wet condition. This ensures that the active ingredients in the waterproof coating can penetrate the moist substrate and effectively perform their function.
4. During the hot summer months, it is best to carry out construction in the early morning or late evening to prevent rapid evaporation of moisture.
5. If decorative materials are to be applied over the waterproof coating, they must be installed only after the coating has fully cured.
6. Waterproof coatings shall be used only on mortar and concrete; they are not suitable for materials such as metal, wood, plastic, glass, gypsum board, foam board, asphalt, rubber, SBS, APP, and polyurethane.
