How to Screed a Floor

A comprehensive guide on how to screed a floor, incorporating different methods and techniques as per professional standards.

Introduction

Screeding a floor is an essential process to ensure a smooth and level surface for flooring applications. There are various screeding methods and types of screeds that can be used depending on the requirement. Here's a step-by-step guide on how to screed a floor successfully.

Types of Floor Screeds

There are three main types of sand and cement screed:

  • Monolithic Screed
  • Bonded Screed
  • Unbonded Screed
  • Floating Screed

Monolithic Screed

Monolithic screeds are laid within three hours of the concrete slab being poured, allowing them to bond chemically with the concrete as they both set and dry. Typical thickness ranges from 12 to 25 mm.

Bonded Screed

This type of screed is laid on a hardened sub-base. The base should be scabbled for a key, and a bonding agent is often used to ensure good adhesion.

Unbonded Screed

Unbonded screeds are not attached to the base and are laid over a damp-proof membrane. Appropriate for new or renovated sub-bases.

Floating Screed

Floating screeds are laid over insulation boards or other insulating material and are often used for underfloor heating systems.

Step-by-Step Screeding Process

Follow these steps to screed a floor:

  1. Preparation: Clean the sub-base thoroughly by removing debris and dust. For bonded screeds, ensure the concrete surface is rough and damp before applying the screed.
  2. Mixing: Use the correct proportions of sand and cement. Ensure the mix is not too wet or too dry. An ideal consistency is when the material forms a tight ball in your hand without falling apart.
  3. Application: Pour the screed mixture over the prepared base. Use screed rails to form a chequerboard framework if you are working on a larger area.
  4. Levelling: Level the screed using a straight edge or a dappling bar to ensure a uniform surface.
  5. Curing: Allow the screed to cure naturally, keeping it damp for about seven days using plastic sheeting or light spraying. Avoid artificial heat to speed up the process as it needs to dry naturally.

Finishing Options

Depending on the intended use, you can finish the floor screed in various ways:

  • Trowel Finish: Achieved using a large steel trowel. Suitable for vinyl tiles or carpets.
  • Float Finish: Provides a coarser texture, ideal for tiling adhesive when laying ceramic tiles.
  • Latex Finish: Suitable for areas requiring a smooth, resilient finish.
  • Free Flow Screed Finish: Used for quick application over larger areas.

Conclusion

Laying a floor screed requires careful preparation, correct mixing, and appropriate finishing techniques. By following these guidelines, you can ensure a durable and level surface for various flooring applications.