Kumar IronUpdated
In this guide
The three families in plain words
- Cementitious: cement based, applied as a slurry or mortar. Rigid to semi-flexible. Bonds well to masonry and concrete.
- Polyurethane (PU): a liquid polymer that cures into a rubbery membrane. Very flexible. Best when a surface is exposed or may crack.
- Bitumen: a black, tar-like material, used as a coating or as sheet membrane. Common under screed and in foundations.
Side by side
These are general patterns, not guarantees. Two products from the same family can behave quite differently, so the data sheet is the final word.
| Property | Cementitious | Polyurethane (PU) | Bitumen |
|---|---|---|---|
| Flexibility | Rigid or semi-flexible. Polymer modified types are better | High. Stretches and bridges movement | Moderate. Can get brittle with age |
| UV resistance | Poor on its own. Keep it covered | Good in UV stable grades, used on exposed terraces | Poor. Degrades in sun |
| Surface needed | Damp, clean masonry or concrete | Dry, clean and sound. Sensitive to moisture in the base | Dry, primed surface |
| Typical use | Bathrooms, tanks, basement walls, under tiles | Exposed terraces, joints, under tiles, balconies | Under screed, foundations, sheet membrane on roofs |
| Cost direction | Usually the lowest | Usually the highest of the three | Mid-range, varies with the membrane type |
| Main risk | Cracks if the slab moves, or thin application | Poor application on wet base, or wrong grade in sun | Exposure to sun, and poor laps at sheet joints |
Flexibility and cracks
A rigid coat is fine on a stable slab, but a slab that expands in summer and shrinks in winter will eventually crack a rigid coat. Polymer modified cementitious products handle small hairline cracks better than plain cement slurry. PU is the choice when you expect movement at joints, at pipe penetrations or where a slab sits on different supports.
Cracks wider than a few millimetres, or cracks that keep growing, need an engineer's look before any coating. A coating can hide a crack, but it cannot hold it closed.
UV and exposed surfaces
Sunlight is the main difference between the families. A cement coat left open to the sun can craze and lose its bond over time, so it should be covered by tiles, screed or a protective topcoat. Bitumen coatings soften, crack and lose their grip in direct sun, so keep them under screed or tiles.
For an open terrace, pick a UV stable PU or an acrylic elastomeric coating, and check that the data sheet says it suits exposed use.
Where each one fits
- Exposed terrace with no tiles: UV stable PU or acrylic elastomeric coat, with a polymer modified cove at the parapet.
- Terrace under tiles or a protective screed: polymer modified cementitious, or bitumen membrane under screed.
- Bathroom floor and walls: polymer modified cementitious, with PU at joints and cracks.
- Water tank: a potable grade product, as covered in our tank and basement guide.
- Basement: crystalline or cementitious systems on the inside, or membranes on the outside when excavation is possible.
- Foundations and under floor membranes: bitumen or sheet membrane, under screed.
Cost direction, not a price list
Cementitious coats usually cost the least per square foot. PU costs more, and the gap is bigger with a two component, high build system. Bitumen cost depends on whether you buy liquid bitumen or sheet membrane. Rates change, so ask us or your dealer for current prices, and compare the cost per square foot including the number of coats, not the price per bucket.
How to choose in four questions
- Is the surface in direct sun? If yes, PU or acrylic elastomeric, or cover the coat.
- Will the surface move or crack? If yes, lean toward PU or a flexible polymer modified coat.
- Is it a wet area or water storage? Check for the potable or wet area statement on the data sheet.
- Is the base damp, dirty or new? PU needs a dry base, and cement needs a damp, clean one.
Frequently asked questions
- Which waterproofing is best for an open terrace?
- A UV stable polyurethane or an acrylic elastomeric coat, applied in two coats with a good parapet cove. Cement coats are usually covered by tiles or screed on open roofs.
- Can PU be used under tiles?
- Yes. Many PU membranes are sold for use under tiles in bathrooms and balconies. Check the data sheet for the tile bond and the coat thickness.
- Is bitumen waterproofing good for a bathroom?
- Bitumen is not a common choice for bathrooms. It suits areas under screed or in foundations. Use a bathroom grade system instead.
- Why did my cement coat crack?
- Usually the slab moved, the base was not prepared, or the coat was applied too thin. Check the crack, fix the base, and use a flexible polymer modified coat or PU at that spot.