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Bonded vs Unbonded Screed
01st September 2022 When it comes to any building, flooring is an essential part of its structure. This means it’s vital to ensure that your floors are sufficiently strong, durable, smooth and level. This can be achieved through screed flooring, but with all the different types available on the market today, you may be unsure as to what one best suits your building’s needs.
There are two main floor screed designs – bonded screed and unbonded screed. To give clarity, specialist concrete contractors Wright Minimix have developed this guide to explain what exactly screed is, the differences between bonded and unbonded screed along with the benefits and uses of each.
Read on to find out more, or contact us today to discuss a screed flooring quote.
What exactly is screed?
Screed is essentially a thin layer that is laid over concrete to create a smooth, sturdy and hardwearing subfloor. Created by mixing cement with graded aggregates and water, screed can be between 25mm and 100mm in thickness, and can be left as a standalone finish or covered with additional decoration (such as carpet or floorboards).
What is bonded screed?
Bonded screed is laid onto a mechanically prepared substrate (or underlying layer) using a bonding agent or slurry. The aim is to maximise the potential bond to the concrete substrate. The optimum thickness of bonded screed is between 25-40mm.
What is unbonded screed?
Unbonded screed, on the other hand is intentionally separated from the substrate by the use of a damp-proof membrane or polyethylene sheet. With unbonded screed, it’s crucial that the drying process isn’t rushed as if it dries too fast, the edges of the screed can warp. It’s recommended that unbonded screed thickness exceeds 50mm.
Will screed stick to concrete?
Technically no as screed is not directly applied to concrete. Screed is applied over a mechanically prepared substrate (if using bonded screed) or a membrane (if using unbonded screed) which is placed over the top of the concrete.
What is the difference between bonded and unbonded screed?
We explain the differences between bonded and unbonded screed and when you would use them below.
When would you use bonded screed?
Typically, bonded screed is ideal for areas that will regularly endure heavy loads such as driveways and car parks.
What are the benefits of using bonded screed?
The advantages of using bonded screed include how:
Bonded screed is simpler to apply as it’s thinner than any other form of screed
As bonded screeds can be much thinner than any other form of screed, this makes the application much simpler as all that’s required is a slurry of cement and water or a bonding agent.
Reduces shrinkage
By applying bonded screed correctly, shrinkage will be reduced in the future due to additives contained in the bonding agent.
When would you use unbonded screed?
As it uses a damp proof membrane to protect against moisture, unbonded screed is best used in buildings where damp presents a serious problem (e.g. for underfloor heating).
What are the benefits of using unbonded screed?
Reasons for choosing unbonded screed include how:
Unbonded screed prevents settlement
Settlement is the term given to when a floor sinks due to large amounts of pressure. Settlement is a common problem with concrete floors, but as the damp-proof membrane separates the screed from the concrete, the risk of settlement is mitigated.
Unbonded screed reduces shrinkage cracking
Shrinkage cracking accounts for about 80% of screed cracking. By separating the screed from the concrete substrate, the risk of shrinkage is greatly reduced during the drying process.
Unbonded screed guards against damp
As already touched upon, thanks to the damp-proof membrane separating the screed from the concrete, a barrier is created to prevent damp rising from the substrate.
Which is better – bonded or unbonded screed?
We don’t believe one screed design is better than the other – it all depends on your project and how you intend to apply the screed; for projects that need to withstand heavy loads on a regular basis, we recommend opting for bonded screeds.
For projects that take place in areas that are prone to moisture and damp, we suggest choosing unbonded screed.
Whether you require bonded or unbonded screed, trust Wright Minimix to provide the right floor solution for your commercial or domestic needs.
Wright Minimix is a specialist concrete and floor screeding company
Wright Minimix specialise in supplying high quality liquid screed flooring, concrete blocks and ready mixed concrete to customers across the South West of England and South Wales. Our team of vastly experienced and skilled concrete contractors pride themselves on giving expert advice across our commercial and residential clients.
To find out how we can provide screed flooring for your property, or to learn more about our wide array of concrete services, don’t hesitate to call our friendly team today on 01179 582090 or alternatively feel free to leave a message on our contact webpage.