PU
Liquid polyurethane
Cures by chemical reaction into a seamless, rubber-like membrane.
- Tiles
- Compatible tile adhesive or protection screed
- Liquid PU membrane
- Primer
- Dry substrate: concrete or screed
System pageLiquid PU
▽ +09.00Comparison
Polyurethane vs cementitious waterproofing
Two systems applied wet on site that work in different ways: a flexible membrane bonded to the surface, or cement-based coats that close the pores of the concrete.
The two options
CEMENT
Cementitious coating
Coats of cement, fine aggregate and additives that bond to concrete and close its pores.
- Tiles
- Cement-based tile adhesive
- Second cementitious coat
- First cementitious coat
- Pre-wetted concrete
System pageCementitious
Example: a wet-area floor under tiles. Illustrative drawing, not to scale; the actual layers follow the approved system.
The key difference
Liquid polyurethane goes on over a primer and cures into a flexible membrane bonded to the surface. It follows movement and bridges hairline cracks, but it needs a dry surface and works on the water (positive) side.
Cementitious waterproofing goes on pre-wetted concrete and becomes part of its surface. Rigid grades resist water pressure and some are made for the negative side; flexible two-component grades tolerate limited movement.
Criterion by criterion
Descriptive criteria, not scores: each cell states the usual behaviour; final values follow the product TDS and the approved specification.
| Criterion | PULiquid polyurethane | CEMENTCementitious coating |
|---|---|---|
| What it is | One- or two-component polyurethane resin. | Cement, fine aggregate and additives, usually polymer-modified. |
| Movement capability | Elastic; follows movement and bridges cracks within the system’s limits. | Rigid grades take no movement; flexible grades take limited movement and hairline cracks. |
| Water pressure & negative side | Positive side only; negative pressure pushes it off the surface. | Rigid grades resist pressure, and some products are made for the negative side. |
| Substrate & moisture | A dry surface within the TDS moisture limits; moisture causes bubbles. | A pre-wetted surface without standing water; tolerates damp concrete. |
| UV exposure | Some systems need a UV-resistant top coat when left exposed. | Unaffected by UV, but rigid grades crack with the thermal movement of exposed roofs. |
| Installation method | A primer, then two or more coats by roller, brush or spray, with reinforced details. | Two coats by brush, trowel or spray on pre-wetted concrete. |
| Weather & curing | Humidity and temperature affect curing; protected from rain until cured. | Needs moist curing; heat and wind cause cracking. |
| Drinking water | Only products approved for drinking-water contact. | Grades approved for drinking water exist and are common in tanks. |
| Detailing | Excellent around drains, penetrations and corners. | Fillets at corners, and reinforcing tape where needed. |
| Typical applications | Roofs, balconies, wet areas, planters and details. | Basements, tanks, pools, wet areas and lift pits. |
| Inspection & testing | Wet-film thickness during application, consumption tracking and a flood test. | Consumption and thickness checks, curing, and a flood or fill test. |
| Repairability | A new coat over a cleaned, abraded surface with the specified primer. | Local repair with the same material after preparation. |
When to choose which
PU
Choose PU when
- Roofs and balconies with thermal movement and many penetrations.
- A surface that can be dried, with water coming from the applied side.
- Where hairline cracks must be bridged.
CEMENT
Choose CEMENT when
- Internal treatment of a basement or lift pit on the negative side.
- Drinking-water tanks, with an approved product.
- Damp concrete that cannot be dried, out of the sun.
Either way
- They often meet in one building: cementitious or crystalline in the basement and tank, polyurethane on the roof and balconies.
- Live cracks and joints are treated first, by injection or a joint system; neither coating handles them alone.
General educational content; final values and requirements follow the manufacturer’s TDS and the approved project specification.
Common questions
Which is better for bathrooms under tiles?
Both work under tiles. Polyurethane suits penetrations and movement; flexible cementitious is a common choice with cement-based tile adhesive. The specification and the surface decide.
Can polyurethane go on damp concrete?
No — unless the system is made for it, with the primer the manufacturer specifies. Moisture rising while it cures causes bubbles.
Does cementitious waterproofing suit an exposed roof?
Rigid grades do not suit exposed roofs because they crack with thermal movement; a flexible membrane is chosen there.
References
Standards that cover these materials — named to show what they cover, not to claim that any product complies.
- EN 14891Liquid-applied waterproofing products used beneath tiling bonded with adhesives: requirements and test methods.
- ASTM D4263Plastic-sheet method for indicating moisture in concrete before coatings.
Technical review
Still weighing the options?
Send the location, area and surface condition, and our engineers will propose the right system after a review.