Your Guide to Choosing the Right Floor Screed
Floor screed may not be the most glamorous part of a building project, but it’s nevertheless, absolutely essential. Screed is the foundation for everything that goes on top – your tiles, carpets, or wooden floors.
It’s what supplies the smooth, level surface you need on a self-build, renovation or DIY project. And if you’re planning to install underfloor heating, screed has to be part of the mix. But with so many different types of floor screed out there, where do you start?
At Capital Screeding, we get that choosing the right floor screed can feel bewildering. It’s easy to get lost in the jargon and overwhelmed by the options. That’s where we come in. In this blog we’ll talk you through the different types of floor screed, explaining what they are, and helping you figure out which one is the perfect fit for your project.
What’s Screed Made Of?
Let’s start with the basics by looking at screed composition. Basically, you’ve got your core ingredients, and then you can add a few extras to make it just right for your job.
The Core Ingredients:
Traditional screed is a mixture of:
- Cement – This is what makes the screed harden and gives it its strength.
- Aggregates – Normally sand or small stones, that give bulk and stability to the screed.
- Water – To mix the cement and aggregates together. Judging the right amount of water is important to arrive at the correct consistency and strength.
Adding a Little Something Extra (Additives):
Sometimes additives are added to the mix. These enhance the screed’s performance in various ways, such as:
- Accelerators – Speeding up the drying time.
- Plasticisers – Making the screed easier to work with.
- Air-entraining agents – Improving the screed’s resistance to extreme temperatures.
Liquid Screed:
Liquid screed uses calcium sulphate as its binder which makes it flow more easily than traditional sand and cement screed. It can be poured quickly and easily, making it ideal for large areas and underfloor heating systems.
Self-Compacting Screed
This type of screed doesn’t need much manual work to level it out. It flows readily and fills all the available gaps, creating a smooth and even surface with minimal effort. This is especially useful if you have a complex floor layout.
Types of Floor Screed
Essential as floor screed is, it needs to be the right type of screed for a successful project. The reason for this is that each type has its advantages and disadvantages, which make it suitable for specific types of project.
1. Bonded Screed
Bonded screed is applied directly to a clean, prepared substrate (like concrete). It’s designed to adhere strongly, so that it becomes an integral part of the flooring.
The bonding happens through mechanical adhesion (the screed keys into the substrate’s surface) and, in some cases, chemical adhesion (using a bonding agent). Often the substrate is best roughened or primed to improve the bond.
- Why it’s used – Bonded screed is used to create durable floors, experiencing heavy foot traffic or loads. It’s commonly used in commercial and industrial settings.
- Advantages – Excellent strength and durability, and has good resistance to cracking and movement, suitable for heavy loads.
- Disadvantages – Needs careful substrate preparation, can be more challenging to install than other types of screed. It’s not suitable for uneven floors.
2. Unbonded Screed
Unbonded screed is laid over a damp-proof membrane (DPM) or a separating layer. It’s not directly attached to the substrate. The separating layer keeps the screed away from the substrate, which allows for independent movement.
- Why it’s used – Unbonded screed is useful when you have a substrate that’s contaminated, uneven, or prone to movement. It’s also used when a DPM is needed to stop moisture rising from the ground.
- Advantages – Can be used where there are substrate imperfections, contaminated substrates, and it provides a barrier against rising damp.
- Disadvantages – It’s not as strong as bonded screed and can be more prone to movement or cracking if there’s movement in the substrate shifts significantly. It’s not suitable for use with very heavy loads.
3. Liquid or Flow Screed (including variations):
Liquid screed, also known as flowable screed, is a self-levelling screed that’s poured or pumped into place. Its fluid consistency allows it to flow and level easily, filling large areas quickly and efficiently.
There are different types, including:
- Anhydrite (Calcium Sulphate) Screed – Known for its smooth finish and suitability for underfloor heating.
- Concrete/Modified Screed – Known for its strength and is often used in commercial applications.
- Why it’s used – Liquid screed is ideal for large areas, underfloor heating systems (as it encases pipes efficiently), and situations needing a very smooth, level finish.
- Advantages – Fast installation, very level, good thermal conductivity (especially anhydrite), less labour intensive than traditional screeds.
- Disadvantages – More expensive than traditional screeds, requires careful planning and sealing to prevent leaks.
4. Floating Screed:
Floating screed is laid on top of insulating material and a DPM. It “floats” above the structural floor. The insulation layer is there for thermal and sometimes acoustic insulation. The DPM prevents moisture from rising.
- Why it’s used – Commonly used in applications where thermal or sound insulation is required, such as in multi-story buildings or homes.
- Advantages – Very good thermal and sound insulation, can be used over uneven substrates.
- Disadvantages – More complex and expensive to install than other types, requiring careful selection of insulation materials.
5. Underfloor Heating Screed:
This refers to screed that’s specifically favoured for use with underfloor heating. Liquid screeds (especially anhydrite) are popular because of their excellent thermal conductivity. The screed should encase the underfloor heating pipes, allowing heat to transfer evenly across the floor surface.
Why it’s used – Screed is necessary to underfloor heating systems. The type of screed chosen needs to be able to provide thermal expansion and contraction associated with heating and cooling.
Advantages – Increases the efficiency of underfloor heating and provides a comfortable and even heat distribution.
Disadvantage – Needs careful consideration of screed thickness and thermal properties, some screeds may not be suitable for underfloor heating.
Unsure Which Screed is Right for Your Project? Let Capital Screeding Help!
Every project is unique, and choosing the correct screed depends on several factors. Our expert team at Capital Screeding can provide the guidance you need to select the perfect flooring solution. Contact us today for a free consultation at 020 3369 3396.
