how to screed surface

Ever walked on a perfectly smooth floor and wondered how they achieved such an even surface? The secret lies in a process called screeding. Screeding is a vital step in many construction projects, ensuring floors are level, smooth, and ready for the final finish. Whether you’re a DIY enthusiast or a professional builder, understanding how to screed a surface is a valuable skill. In this guide, we’ll walk you through everything you need to know about screeding, from the tools required to the finishing touches.

What is Screeding?

Definition and Purpose

Screeding is the process of applying a well-blended mixture of cement, sand, and water to a surface, creating a smooth, level base. This base can then support a variety of floor finishes like tiles, carpet, or hardwood. The primary purpose of screeding a floor step is to even out surfaces, ensuring they are flat and free from bumps or dips.

Types of Screeding

There are several types of screeding, each suited to different applications:

  • Bonded Screed: Screed that is bonded directly to the substrate, usually used in thin applications.
  • Unbonded Screed: Laid over a separating membrane, used when the substrate isn’t suitable for bonding.
  • Floating Screed: Applied over insulation or underfloor heating, not bonded to the substrate.

Tools and Materials Needed for Screeding

Essential Tools

To screed a surface effectively, you’ll need the following tools:

  • Screed board or straightedge
  • Mixing bucket or mixer
  • Trowel
  • Float
  • Level guides
  • Shovel

Recommended Materials

The basic materials required for screeding include:

  • Cement
  • Sharp sand
  • Water
  • Primer (for bonding)
  • Additives (optional, for enhanced properties)

Preparing the Surface for Screeding

Cleaning the Surface

Before screeding, ensure the surface is clean and free from debris, dust, oil, or any contaminants that could affect adhesion. Sweep and vacuum the area thoroughly.

Priming the Surface

Applying a primer helps in bonding the screed to the substrate. Follow the manufacturer’s instructions for the correct application and drying times.

Setting Up Level Guides

Level guides are crucial for achieving a flat surface. Set up these guides using a laser level or spirit level, ensuring they are perfectly horizontal and at the desired height of the screed layer.

Mixing the Screed

Types of Screed Mixes

The screed mix can vary depending on the specific requirements:

  • Traditional Cement-Sand Screed: A mix of 1 part cement to 3-5 parts sand.
  • Self-levelling Screed: A flowable mix that levels itself with minimal intervention.
  • Fast-drying Screed: Contains additives to speed up the drying process.

Mixing Techniques

Mix the screed in a large container or mixer, combining the dry components first before gradually adding water. Aim for a semi-dry consistency, where the mix holds together when compressed but isn’t too wet.

Applying the Screed

Pouring the Screed

Pour the mixed screed onto the prepared surface, starting from the farthest corner and working towards straight edge of the exit.

Levelling the Screed

Using the screed board or straightedge, level the screed by dragging the board across the surface in a sawing motion. Ensure the screed is compact and any air pockets are eliminated.

Using a Screed Board

A screed board helps in achieving a flat, even surface. Work methodically, section the floor step by step by section, and continuously check the level as you go.

Finishing the Screed

Smoothing the Surface

After levelling, use a float to smooth the surface. This step is crucial for achieving a polished finish and preventing any high spots.

Curing the Screed

Curing is essential to prevent cracks and ensure the screed reaches its full strength. Cover the screed with polythene sheeting and keep it moist for at least 7 days.

Common Mistakes in Screeding and How to Avoid Them

Uneven Surface

An uneven surface is often due to incorrect levelling. Always use level guides and frequently check your work with a spirit level.

Poor Mixing

Improperly mixed screed can lead to weak spots. Ensure a consistent mix by thoroughly combining the components.

Inadequate Curing

Skipping the curing process can result in a brittle screed. Always allow sufficient time for curing and maintain moisture levels.

Advanced Screeding Techniques

Power Floating

Power floating involves using a mechanical trowel to smooth and compact the screed. This technique is often used for large commercial projects.

Use of Fibers in Screed

Adding fibers to the screed mix can improve its strength and reduce the risk of cracking. Fibres distribute stress throughout the screed, enhancing structural performance and its durability.

Screeding for Different Surfaces

Indoor vs Outdoor Screeding

Indoor screeding requires a smooth, even finish for flooring, while outdoor screeding must account for drainage and weather resistance.

Screeding Over Underfloor Heating

When screeding over underfloor heating, use a flexible screed mix that can accommodate thermal expansion and contraction.

Troubleshooting Screed Problems

Cracks in the Screed

Cracks can occur due to poor curing or rapid drying. Address these by maintaining proper curing conditions and using crack repair compounds.

Screed Not Drying Properly

If the screed remains damp, it could be due to high humidity or insufficient ventilation. Ensure the area is well-ventilated and consider using dehumidifiers.

Maintenance of Screeded Surfaces

Regular Cleaning

Maintain screeded surfaces by regularly sweeping and cleaning to prevent dirt buildup and staining.

Repairing Damaged Screed

For minor damage, use a repair mortar. For extensive damage, consider re-screeding the affected floor area.

Benefits of a Properly Screeded Surface

Durability

A well-screeded surface is robust and can withstand heavy traffic and loads.

Aesthetic Appeal

Smooth, level surfaces provide an excellent base for various flooring finishes, enhancing the overall look of the space.

Environmental Considerations in Screeding

Eco-friendly Materials

Opt for environmentally friendly materials, such as recycled aggregates and low-carbon cement, to reduce the environmental impact.

Sustainable Practices

Adopt sustainable practices, like efficient mixing and minimizing waste, to promote eco-friendly construction.

What is Bonded Screed?

how to screed surface

Bonded screed is a type of floor screed that adheres directly to the concrete sub or substrate below. Unlike other screeds, which might float or sit unbonded over an intermediate layer, bonded screed is fixed to the concrete or existing flooring, creating a strong and unified surface.

The Purpose of Using Bonded Screed

Bonded screed flooring serves several key purposes. Primarily, it enhances the strength and durability of the flooring, making it ideal for high-traffic areas. It’s commonly used in both residential and commercial settings where a robust, long-lasting floor is essential.

Ideal Applications and Scenarios

You’ll often find bonded screed in garages, workshops, and industrial spaces where heavy loads are the norm. It’s also perfect for refurbishment projects where the existing substrate needs reinforcement.

Types of Bonded Screed

Traditional Bonded Screed

This is the most common type of bonded cement screed, made from a mixture of cement and sand. It’s known for its durability and cost-effectiveness.

Polymer-Modified Bonded Screed

Adding polymers to the concrete mix also can enhance the flexibility and adhesion properties of the screed. This type is particularly useful in areas with high foot traffic or where slight movements in the substrate are expected.

Benefits of Bonded Screed

Improved Load-Bearing Capacity

Thanks to its direct bond with the substrate, bonded screed can support heavier loads compared to unbonded or floating screeds.

Enhanced Longevity of Flooring

A well-applied bonded screed can significantly extend the life of your flooring, making it a cost-effective choice in the long run.

Resistance to Cracking and Shrinkage

Properly mixed and applied bonded screed is less prone to cracking and shrinkage, ensuring a smooth and even surface.

What is Unbonded Screed?

how to screed surface

Unbonded screed is a type of floor screed that is laid over a separating layer, typically a damp-proof membrane or insulation. Unlike bonded screed, which adheres directly to the substrate, thin layer of unbonded screed sits atop this intermediate layer, providing a level surface for the final floor covering.

Types of Unbonded Screed

Traditional Unbonded Screed

This type of screed is made from a mixture of cement and sand, laid over a damp-proof membrane or insulation. It’s widely used for its cost-effectiveness and ease of application.

Fiber-Reinforced Unbonded Screed

Incorporating fibers into the screed mix enhances its strength and flexibility. Fiber-reinforced unbonded screed is ideal for areas subject to heavy foot traffic or minor movements in the substrate.

What is Floor Screed?

how to screed surface

Floor screed is a layer of material that is applied over a concrete slab or directly onto the concrete substrate to create a smooth, level surface. It acts as a base for floor coverings such as tiles, wood, or carpet, providing structural support and enhancing thermal and acoustic insulation within a building.

Screeding might seem daunting at first, but with the right tools, materials, and techniques, it becomes manageable. Whether you’re aiming for a durable industrial floor or a smooth concrete base for your living room tiles, screeding is a crucial step in achieving a flawless finish. Remember, preparation and patience are key. So, gather your tools, follow this guide, and start screeding like a pro!

 

FAQs

What is the ideal thickness for a screed layer?

The ideal thickness for a traditional screed top layer is typically between 40mm and 75mm, depending on the application and type of screed used.

Can I screed over an existing, concrete flooring anyway?

Yes, you can screed over an existing concrete floor, provided it is clean, sound, and properly prepared enough screed with a primer or bonding agent.

How long does screed take to dry?

Screed typically takes 24-48 hours to dry enough to walk on, but it can take up to 28 days to fully cure, depending on the mix and environmental conditions.

What is the difference between screed and concrete?

While both screed and concrete are made from cement, sand, and water, screed is finer and smoother, designed for surface finishing, whereas concrete is coarser and used for structural purposes.

Is it necessary to seal a screeded floor?

Sealing a screeded floor can enhance its durability and resistance to moisture and stains, but it is not always necessary depending on the final floor finish.