Application guides
Applying a liquid-applied PU waterproofing membrane
Alainz Technical Team
A liquid-applied polyurethane membrane only performs to its datasheet if it is applied to the datasheet. Failures are almost always application failures (a damp or contaminated substrate, an inadequate dry film thickness, or an insufficient cure before flooding), not product failures. This is the general sequence; the manufacturer's own datasheet and method statement always govern the specific product.
1 · Substrate preparation
The substrate must be sound, clean, dry and free of laitance, curing compounds, oil and dust. New concrete is typically allowed to cure (commonly ≥28 days) and moisture must be within the product's stated limit. Fillets are formed at wall-to-floor junctions and cracks are treated per the datasheet.
2 · Priming
A primer appropriate to the substrate (and its porosity) is applied at the stated coverage and allowed to reach the specified tack/over-coat window before membrane application. Priming outside that window is a common cause of blistering and poor adhesion.
3 · Membrane application & dry film thickness
| Parameter | Why it matters | Where it's stated |
|---|---|---|
| Coverage / consumption | Determines the achieved thickness | kg/m² per coat, datasheet |
| Number of coats | Even build, no pinholes | Datasheet method |
| Dry film thickness (DFT) | The performance-critical figure | mm, datasheet |
| Reinforcement | At joints, upstands, penetrations | Detail drawings |
| Recoat window | Inter-coat adhesion | Hours, datasheet |
The membrane is applied in the stated number of coats to reach the specified DFT, the single most important field parameter. Wet-film-thickness gauges during application and DFT checks after cure are how the specified thickness is evidenced.
4 · Curing and flood test
The membrane is protected and allowed to cure fully before any water test or overlay. A flood (water) test, typically holding water over the area for a defined period (commonly 24–48 h) and checking below, is the standard acceptance test before protection boards and screeds go down.
General reference only. Application must follow the specific product's datasheet and method statement, the project specification, and the responsible engineer's requirements, including any warranty conditions, which often mandate manufacturer-approved applicators.