What each one actually is
Cement render is sand, cement, lime and water. It has been used for a very long time, it is hard, it breathes well, and it bonds mechanically by keying into a porous surface.
Acrylic render is the same basic idea with polymers added to the mix. Those polymers change the behaviour of the material substantially. They make it flexible, they dramatically improve how well it sticks, and they make the finished surface far less permeable to wind driven rain while still letting vapour escape from inside the wall.
Neither is better in general. They are good at different things, and the wall decides which one you need.
Where cement render wins
On solid, stable masonry, cement render is still the right answer. Double brick, blockwork and concrete are all ideal substrates for it.
It is cheaper, roughly thirty to fifty percent less than an acrylic system. It is harder, so it takes knocks better. And it breathes more freely, which matters a great deal on older buildings where the wall needs to be able to release moisture.
On heritage brickwork it is not just preferable, it is necessary, though with a much higher lime content than a modern mix. A hard modern render on soft old sandstock brick will slowly destroy the brick behind it.
Where acrylic render wins
There are four situations where acrylic is worth the extra cost and one where it is not optional at all.
- Coastal exposure. Salt attack is the leading cause of render failure from Bondi to Cronulla, and acrylic sheds salt far better than a plain cement finish
- Reactive clay sites. Much of western and south west Sydney sits on soil that swells and shrinks seasonally, and a flexible coating absorbs that movement instead of cracking
- Dark colours and west facing walls, where surface temperature swings are extreme and thermal cycling opens up rigid coatings
- Anywhere a colour through finish is wanted, so there is no paint film to blister, fade or peel
- Blueboard, Hebel and other lightweight panels. This is the not optional one. Standard cement render on panel substrates will crack along every sheet joint
The answer most Sydney jobs end up with
In practice, a large share of jobs use both. A cement render base coat to get the wall flat, true and properly bonded to the masonry, then an acrylic texture coat over the top for flexibility, colour and weather resistance.
That combination gets you the hardness and breathability of cement where it matters, against the substrate, and the flexibility and UV stability of acrylic where it matters, at the surface. It also usually costs less than a full acrylic system while performing close to one.
How to tell which one you have already
If you are trying to work out what is on your wall now, a few signs help. Cement render is harder, it sounds sharper when you tap it, and where it has chipped you will see a sandy grey mineral edge all the way through.
Acrylic render is slightly softer, has a marginally rubbery feel, and where it chips you often see a colour that runs consistently through the material rather than a painted surface over grey.
The most reliable indicator is the building. If it is brick and pre 1990, it is very likely cement render. If it is a modern build with lightweight panel walls, it is almost certainly an acrylic system.
What we would recommend
If your wall is solid brick or block, inland, in reasonable condition, and you want the best value, go cement render with an acrylic texture coat over it.
If your wall is near the water, on reactive clay, in a dark colour, or made of blueboard or Hebel, go acrylic and do not compromise on it. The price difference is a fraction of the job. The difference in how long it lasts is measured in years.
If you are not sure which situation you are in, that is exactly what a free on site quote is for.