How to Screed a Floor – The Ultimate Guide

Your home or property demands a level of perfection that can only be achieved through attential to detail.

From the foundation to the roof, every aspect must be meticulously crafted to ensure a flawless finish. One of the most critical steps in this process laying screed onto the floor, a technique that creates a smooth, level surface for your flooring material.  Properly laid with under-screed insulation will ensure your floor can provide a level of impact sound insulation.

Whether you’re a DIY enthusiast or a professional contractor, mastering the art of screeding is essential for achieving a flawless finish. In this ultimate guide, we’ll take you through the step-by-step process of screeding a floor including the types and techniques needed to achieve a perfect result every time. So, let’s dive in and discover the secrets to screeding like a pro.

What Is a Screed?

Screeding, a term is often thrown around in construction circles, is a crucial component of the building process. It’s a thin layer of cement-based material that is applied to the concrete subfloor, to create a smooth, level surface upon the final flooring to be laid upon. This seemingly simple process requires a trained eye and a steady hand to ensure flawless results.

Screeds, often referred to as “the foundation of the foundation,” are a necessary step in a stable and structurally sound building. It’s the unsung hero that provides the backbone of the flooring system, ensuring that it can withstand the test of time and the weight of heavy foot traffic.

This versatile material comes in various forms, including traditional sand and cement, self-leveling, and even eco-friendly options. Each type of screed has its unique properties and benefits, depending on the project’s needs and specifications.

The process of applying a screed is an art form in itself. The skilled craftsmen who undertake this task must have a keen eye for detail and an expert understanding of the materials they are working with and under screed insulation methods. They meticulously mix the screed to the correct consistency, ensuring that it is smooth and free of lumps and bumps.

Once applied, the screed must be left to dry and cure, a process that can take several days. During this time, it’s crucial to maintain the insulation panels at correct temperature and humidity levels to ensure the screed dries evenly and without cracking – all of which require professionally installed screed insulation.

All in all, a screed may seem like a small component in the grand scheme of things, but it’s a vital one that plays a crucial role in the construction process. It’s the foundation upon which the final flooring is laid, and without it, the building’s stability and durability would be compromised.

What Are the Different Types of Screeds?

There are three main types of screed used in the marketplace: bonded, unbonded, and floating screeds.

1. Bonded screed is a mix of sand and cement that is applied directly to the concrete substrate. It is then leveled and compacted to form a hard-wearing surface. This type of screed is often used in areas where there is a lot of foot traffic, as it is durable and provides a good level of insulation.

2. Unbonded screed is a mix of sand and cement that is applied to a damp concrete substrate. It is then leveled and compacted to form a hard-wearing surface. This type of screed is often used in areas where there is a lot of foot traffic, as it is durable and provides a good level of insulation.

3. Floating screed is a mix of sand and cement that is applied to a dry concrete substrate. It is then leveled and compacted to form a hard-wearing surface. This type of screed is often used in areas where there is a lot of foot traffic, as it is durable and provides a good level of insulation.

In addition to these three main types of screed, there is also a fourth type known as liquid screed or self-compacting screed. This type of insulated screed is a mix of calcium sulfate and water, and it sets quickly, usually within 24-48 hours. It is ideal for use in most underfloor heating system installations and is available in thicknesses of 30mm or 40mm depending on whether it is unbonded or ‘floating’.

How to Prepare to Lay an Unbonded Screed

If you’re looking to lay an unbonded screed, then preparation is key. This is a task that requires precision, patience, and attention to detail. But fear not, with these five simple steps, you’ll be well on your way to a perfectly leveled and smooth surface that’s ready for anything.

Step 1: Clear the Surface

Before you start laying your unbonded screed, you need to ensure that the surface or concrete floor you’re working on is clean and free from any debris or dust. This is crucial for achieving a smooth finish, and it will help to ensure that the screed bonds properly.

Step 2: Install a Damp Proof Membrane

A damp-proof membrane is essential when laying an unbonded screed. This will prevent any moisture from seeping up into your screed and causing damage over time. Make sure to install the membrane in accordance with the manufacturer’s instructions.

Step 3: Lay Screed Insulation

Screed on insulation is IMPORTANT! It is vital for preventing thermal heat loss and providing a level of impact sound insulation. It’s important to lay your insulation before you start laying your screed to ensure that it’s properly secured in place.

Isolgomma Roll is a popular method of soundproofing a screeded floor. Manufactured from SBR resilient rubber, it is 5mm thick and is installed below the screed along with an acoustic edge strip to reduce the risk of thermal and acoustic flanking sound transmission.

Isolgomma Uproll is a 9mm thick high-performance underlayment for under screed insulation and acoustic floating floors for both residential and commercial use and can also incorporate underfloor heating systems. Its unique distribution of rubber granules on the floor ensures excellent elasticity and provides superior floor impact sound and acoustic insulation and performance. Isolgomma Uproll has an impact sound reduction value of ∆Lw ≥ 24 dB. The inherent low dynamic stiffness of ≤ 11 MN/m³ is particularly suitable under heavy-duty screeds.

For high-performance acoustic floating floors Isolgomma Upgrei, Highmat or Point can be used. Typically these are used for gyms, cinemas, concert halls, high-sensitivity testing floors and recording or rehearsal studios.  They can be designed to accommodate any depth of screed to meet the highest acoustic and thermal performance requirements.

Step 4: Lay the Screed Base

Once your insulating surface is cleared and prepared, it’s time to lay your screed on the under screed insulation. This will provide a level and stable foundation for your unbonded screed. Make sure to use a high-quality screed mix and follow the manufacturer’s instructions carefully.

Step 5: Install Expansion Joints

Expansion joints are important for allowing your screed to expand and contract without cracking. Make sure to install them in accordance with the manufacturer’s instructions and place them at regular intervals.

Remember, preparation is key, so take your time, follow the instructions, and enjoy the satisfaction of a job well done.

How to Prepare to Lay a Bonded Screed

Enlisted are 4 simple steps that will help you get ready to lay your bonded screed.

Step 1: Surface Preparation

Before starting any screed installation, it’s crucial to prepare the surface. This includes removing all dust, debris, and loose particles. The surface must be clean, dry, and free of any contaminants that could affect the bonding of the screed. A perfectly the prepared surface will provide an excellent base for the screed to bond to, ensuring a seamless finish.

Step 2: Priming

Once the surface is clean and dry, it’s time to prime. Priming is a critical step in the screed installation process, as it creates a barrier between the concrete slab or substrate and the screed. This barrier prevents any moisture from seeping into the screed, which could cause it to crack or fail. Proper priming also enhances the bonding properties of the screed, ensuring it adheres well to the surface.

Step 3: Mixing the Screed

Now that the surface is prepped and primed, it’s time to mix the screed. Careful attention must be paid to the mixing process, as it’s essential to achieve the correct consistency. The screed should have a smooth texture and be free of lumps. A perfectly mixed screed will ensure that it spreads evenly and smoothly, creating a smooth and level surface.

Step 4: Laying the Screed

Finally, it’s time to lay the screed. This step requires expertise, as it’s crucial to ensure that the screed is spread evenly and smoothly. A skilled screeder will use a screed bar to distribute the screed evenly, ensuring that it’s level and has a smooth finish. It’s important to work quickly as the screed sets rapidly, and any delay could cause it to dry unevenly.

How to Lay Screed

Now that we have covered the basics of how to lay a screed and the importance of installing an insulated floor screed, let’s take a look at some practical tips and advice for getting the job done right.

1. To achieve an even finish and make the work easier, we recommend dividing the floor into sections. You can use timber battens as a guide for this purpose. Firstly, apply a small amount of screed to the floor and then lay the battens on top in strips. Ensure that you space the guides approximately 10ft apart and use a spirit level to check their levelness. Wet the battens before laying them down to make their removal easier after finishing the job.

2. To avoid walking on the screed when leaving the room, begin laying the screed from the furthest section from the entrance. This means that the screed can now be started in that section.

3. To fill around 2ft of the first section, take enough screed and spread it out with a trowel.  Then use a screed board or a straight-edged tool to compact and flatten it out. For the best results, use a chopping motion. Alternatively, there are vibrating screed boards available along with other compacting tools.

4. To level the screed after it has been laid to fill the section, you can use a screed board or a piece of timber/another straight edge. Place the straight edge over the battens, ensuring it rests on each side, and move it down the length of the section using a sawing motion. It’s advisable to keep the straight edge tilted slightly so that the sharper edge remains in contact with the screed.

5. After creating a level and even section of the screed, it’s important to repeat the same process in the subsequent sections. Once you have filled two sections, remove the batten and fill the gap between them while ensuring that it remains level and even.

6. Once the whole floor has been screeded, it’s time to finish the concrete by using a bull float. After this step, wait for all the excess water to evaporate or stop coming out of the concrete and repeat the process. If you want to add some texture to the concrete surface, use a wooden float and make arched motions across the surface. Alternatively, if you prefer a smooth finish, use a steel trowel flat against the surface.

7. Once the screed has been laid, it is important to cure it properly. The most common method for doing so involves placing sheeting over the screed and sealing it around the edges. This sheeting should remain untouched for approximately 7 days to allow for proper curing.

8. After the 7-day period has elapsed, the screed should be left to dry for an additional three weeks before any flooring is installed. This extended drying period is critical to ensure that the screed is fully cured and ready to support the weight and traffic of the flooring materials.

By following these guidelines, you can help ensure that your screed is properly cured and ready for the next steps in your construction or renovation project.