How to Screed a Floor: An In Depth Guide

Knowing how to screed a floor is an essential skill if you want to create a perfectly smooth and level surface for your new flooring. Whether you’re renovating a room or laying a screed for tiles or hardwood, mastering this process makes all the difference in achieving a durable, flawless finish.

In this guide, we’ll walk you through each step of screeding, provide practical tips, and highlight the tools you’ll need to transform your subfloor into the ideal foundation for your next project. To help guide you, we’ve included expert tips and insights from seasoned professionals in the industry: Sigma Screed. With over 30 years of experience, Sigma Screed has built a reputation as a trusted supplier and installer of liquid screed, traditional screed, and floor preparation solutions for both commercial and residential projects. For those looking for professional assistance, companies like Sigma Screed are the go-to for expert floor preparation and screeding services.

What is Floor Screeding?

Floor screeding refers to applying a layer of screed mix over a subfloor to create a smooth and level surface for your flooring. The screed layer acts as a foundation for the final floor finish, whether it’s tiles, wood, or carpet.

You have a few types of screed to consider: bonded screed, unbonded screed, and floating screed. Let’s break down these different types of screeds.

• Bonded Screed: This type of screed directly adheres to the concrete subfloor using a bonding agent. It’s an excellent choice for areas that will experience heavy traffic.
• Unbonded Screed: This type sits on a separating layer like polyethylene sheeting or plastic sheets, making it ideal in applications where a damp proof membrane or another form of waterproofing is needed.
• Floating Screed: This type of screed is laid over an insulation layer and is common with wet underfloor heating systems making it popular for homes looking to optimise energy efficiency.

Preparing the Floor

To properly screed a floor, preparation is essential. Follow these initial steps to get started:

Step 1: Clear the Area

First, remove any loose particles or debris from the subfloor using a floor scabbler, a shot blaster, or a chipping hammer. Make sure the entire surface is free of airborne particles. You want the subfloor to be clean and ready for the next step.

Step 2: Apply a Damp Proof Membrane

For concrete flooring, it’s important to add a damp proof membrane, usually made from polythene sheets or PVC sheets. This prevents moisture from the concrete subfloor from damaging the screed layer. 

Step 3: Install Edging Foam

Place edging foam around the walls to prevent cracking caused by screed shrinking as it cures. This compressible material allows for natural expansion and contraction, which prevents micro cracks and helps maintain a smooth finish. 

Step 4: Prepare the Screed Mix

Use a combination of sharp sand and cement to create the screed mix. Typically, traditional sand mixed with cement in a ratio of 4:1 or 3:1 works well. If you want more strength, add polypropylene fibres or other additives to help bind the mix and prevent shrinkage cracks. 

Laying the Screed – Floor Step by Step

Now that you’ve prepped the subfloor, it’s time to start the screeding process. Let’s take a floor step-by-step approach to get your screed level and smooth.

Step 1: Mixing and Laying the Screed

Ensure you have enough screed mixed before you begin so that you don’t run short partway through. Spread the screed mix evenly across the entire floor using a hand tamper or a bull float to compact it into a solid, uniform layer. Be sure to lay the mix in small sections, especially if you’re working with underfloor heating, to avoid rushed work and poor compaction.

Step 2: Levelling the Screed

Next, level the surface using a screed board. You can use a straight piece of wood or a very straight piece of metal as your screed board. Use a sawing motion to even out the screed mix and remove any excess. This process requires patience—be sure to check with a spirit level to ensure the floor is perfectly level. Repeat until you’ve screeded the entire floor.

Step 3: Smoothing the Surface

After levelling, use a steel trowel to smooth the surface. If you’re aiming for a fine finish, you can also use a wooden float or power float. This step helps eliminate high spots and leaves the floor with a nice, smooth finish. For added precision, use a screed level to make sure every section is as flat as possible.

Step 4: Allow Time for the Screed to Dry

The drying process for a screed floor takes time. You should allow at least three weeks for the screed to cure fully. During this time, prevent heavy vehicle traffic or footfall on the new floor, as it can lead to poor compaction or uneven areas. Covering the screed with polythene sheets can help retain moisture and promote even drying.

Tips for Achieving the Perfect Floor Screed

Here are some additional tips that will help you achieve a flawless screed flooring.

• Additives for Strength: Adding styrene butadiene rubber, PVA glue to the screed mix can help improve its strength and bonding properties, particularly for a bonded screed.
• Avoid Excess Water: Using too much water can weaken the screed, leading to cracks. You want just enough to make the mix workable.
• Use Dividers for Large Areas: When screeding large rooms, use your own dividers to separate sections and make the work more manageable.
• Address Micro Cracks: Micro cracks can form if the screed shrinks too fast during the drying process. Keep an eye on the surface and prevent drafts that could speed up the drying.

Floating Screed and Underfloor Heating

For homes with underfloor heating, laying a floating screed is a fantastic way to ensure efficient heat distribution. The key here is to use a layer of compressible material between the screed mix and the underfloor heating pipes. You will also want to make sure the screed layer is compact enough to provide a stable foundation, while still allowing for proper expansion. Always use a bonding agent to increase adhesion and prevent shifting over time.

Tools You Will Need to Screed a Floor

Here’s a handy list of tools to ensure your screeding process runs smoothly:

• Spirit Level: To check that the entire floor is perfectly level.
• Screed Board (Straight Edge): For levelling the screed mix.
• Hand Tamper or Bull Float: To compact the screed layer.
• Steel Trowel/Wooden Float: For achieving a smooth finish.
• PVA Glue/Bonding Agent: For a bonded screed.
• Floor Scabbler/Chipping Hammer: For preparing the subfloor.

Addressing Common Screed Issues

While screeding a floor, some common issues may arise, such as:

• Poor Compaction: This results from not using enough pressure during the screeding process. Make sure to use a hand tamper to compact the mix thoroughly.
• Screed Shrinks: As the screed dries, it can shrink, leading to small cracks. Adding polypropylene fibres to the mix or using edging foam can help minimise this.
• Micro Cracks: These are often caused by a rushed drying process. To avoid micro cracks, ensure the room has stable humidity and temperature during the drying phase.

Testing Moisture Content

Before applying floor coverings, it is vital that the screed is adequately dry. To test screed moisture content, ensure the area is clean, then use a calibrated hygrometer or moisture meter. Place the device on the surface or in a drilled hole for a deeper reading, allowing it to stabilise before recording. Take multiple readings across the area for accuracy. A moisture content below 75% RH is ideal for most flooring installations.

Final Steps for a Flawless Floor

Once you have screeded the entire surface and allowed it to dry completely, it’s time to lay your final flooring. Whether you opt for tile, carpet, or wood, make sure the screed flooring is free from loose particles and that it has cured completely. If the screed layer appears uneven or not perfectly level, use a self-levelling screed mix to create a final, ultra-flat base.

By following these steps, you can screed a floor confidently, knowing you’ve provided a smooth, level, and stable foundation for your new flooring. The process might seem daunting at first, but with the right preparation, tools, and patience, you’ll soon master the art of floor screeding, transforming your concrete subfloor into a flawless, level surface that will stand the test of time.