Single-Part Oil-Based Polyurethane Coating – Underground Application & Special Treatments
1. Core Characteristics of Single-Part Oil-Based PU
• Moisture-curing type (reacts with air/underground base moisture to harden)
• No on-site mixing; ready to use directly
• Mainly for underground concrete basement, pipe gallery, foundation slab, side wall waterproofing & anti-corrosion
2. Step-by-Step Application Method
Step 1: Substrate Preparation (Most Critical)
1. Concrete surface must be solid, clean, dry, no loose mortar, dust, oil, laitance.
2. Repair cracks, holes, honeycombs with cement repair mortar; fill all voids fully.
3. Round all internal/external corners into arc transition (R ≥ 50mm) to prevent coating cracking.
4. Substrate requirement:
◦ Surface no standing water
◦ Moisture content ≤ 9%
◦ Surface temperature: 5℃ ~ 35℃ for construction
Step 2: Priming Coat
1. Stir single-part oil PU evenly before use (no mixing with other materials).
2. Apply primer thinly and uniformly by roller/brush.
3. Coverage: 0.25～0.35 kg/m²
4. Air dry until tack-free (3～6 hours) before top coating.
Step 3: Reinforce Detailed Parts First (Underground Must-Do)
Treat weak points first before large-area painting:
• Pipe penetrations, wall pipe roots
• Construction joints, expansion joints
• Corners, slab-wall junctions
Practice:
• Brush extra single-part PU around details, width ≥ 250mm
• For joints: embed sealing putty first, then brush reinforced PU layer; can add fiberglass mesh for strengthening.
Step 4: Main Coating Application
1. Stir paint thoroughly each time before use.
2. Apply 2～3 cross coats (vertical wall 3～4 coats).
3. Each coat applied perpendicular direction to the previous one.
4. Interval between coats:
◦ Normal temperature: 8～12 hours
◦ Low temperature: extend to 24 hours
5. Final total dry film thickness: 1.2～2.0 mm (standard underground waterproofing).
Step 5: Curing & Protective Layer
1. Natural curing: 24～48 hours full hardening; keep ventilated, no water soaking during curing.
2. After full curing: make 20mm thick cement mortar protective layer before backfill/earthing.
3. Optional: do closed water test / water seepage inspection before covering.
3. Special Required Treatments for Underground Conditions
1. Groundwater & Humidity Special Treatment
• Single-part PU relies on moisture to cure, but surface standing water is forbidden (causes blistering, peeling).
• High water table area:
◦ Do drainage first (drainage board / blind ditch)
◦ Lower groundwater level before coating
• Keep underground construction space well ventilated to avoid excessive local humidity.
2. Low Temperature & Cold Environment Treatment
• Do not construct below 5℃; curing will stop completely.
• In cold weather: store paint indoors in advance, warm up slightly before use (no open fire heating).
• Extend interval time between coats and full curing time.
3. Anti-Crack & Structural Settlement Treatment
• Underground concrete has settlement and micro-cracks easily.
• Add fiberglass mesh cloth sandwiched between middle coating layers to improve crack-bridging performance.
• All expansion joints must use flexible sealing filler + reinforced PU coating, cannot paint directly.
4. Safety & Ventilation Special Treatment
Oil-based single-part PU contains organic solvents, underground space is closed:
• Must keep forced mechanical ventilation all the time.
• Strictly prohibit open flame, smoking, spark equipment (flammable solvent vapor).
• Workers wear gas respirator, protective gloves and overalls.
5. Anti-Corrosion & Soil Chemical Treatment
• Underground soil/groundwater has acid, alkali, salt corrosion:
◦ Increase coating thickness to ≥2.0mm
◦ Do not dilute with water; only use designated PU special solvent if dilution is needed
• Avoid contact with strong acid liquid during curing period.
6. For Wet & Damp Base Special Handling
• If substrate is slightly damp (no running water): allow natural air dry + enhanced ventilation.
• Do not apply on wet fresh concrete; concrete must cure at least 28 days before coating.
Key Summary Rules
1. No mixing, just stir well before use.
2. No standing water on surface; damp is allowed for curing, ponding is not.
3. Corners/joints/pipe roots must be reinforced first.
4. Closed underground site: ventilation + no open flame is mandatory.
5. Must make cement protective layer after curing before backfilling.
Post time: May-08-2026