How much levelling compound do I need per m2?

A standard rule of thumb is that you need approximately 1.7kg of powder per square metre for every 1mm of depth. So, for a 5mm depth over 10m², you would need 85kg of compound (roughly four 20kg bags).

Do I need to prime the floor before screeding?

Yes, priming is essential. It seals the substrate to prevent air bubbles (pinholes) from rising through the screed and stops the subfloor from sucking the moisture out of the mix too quickly, which can cause the screed to crack or fail to level.

How long until I can walk on self-levelling screed?

Most modern 'fast-set' compounds are walk-on within 2 to 4 hours. however, you usually need to wait 12 to 24 hours before laying final floor coverings like LVT, laminate, or carpet.

What is the difference between water-based and latex screed?

Water-based compounds are standard for most concrete subfloors. Latex-based (two-part) screeds are more flexible and are often required when levelling over plywood, chipboard, or existing tiles where slight movement might occur.

How much levelling compound do I need per m2?

A standard rule of thumb is that you need approximately 1.7kg of powder per square metre for every 1mm of depth. So, for a 5mm depth over 10m², you would need 85kg of compound (roughly four 20kg bags).

Do I need to prime the floor before screeding?

Yes, priming is essential. It seals the substrate to prevent air bubbles (pinholes) from rising through the screed and stops the subfloor from sucking the moisture out of the mix too quickly, which can cause the screed to crack or fail to level.

How long until I can walk on self-levelling screed?

Most modern 'fast-set' compounds are walk-on within 2 to 4 hours. however, you usually need to wait 12 to 24 hours before laying final floor coverings like LVT, laminate, or carpet.

What is the difference between water-based and latex screed?

Water-based compounds are standard for most concrete subfloors. Latex-based (two-part) screeds are more flexible and are often required when levelling over plywood, chipboard, or existing tiles where slight movement might occur.

Screed Calculator

Estimate compound requirements for a perfectly flat floor.

Floor Area (m²)

Average Depth (mm)

Screed Requirements

Levelling Tip: Most compounds have a very short working time (usually 20-30 minutes). For large areas, always have a second person helping to mix the next bag while you are pouring and spreading the previous one with a spiked roller.

The Foundation of Finish: Self-Levelling Guide

Smooth & Level

A perfect floor finish depends entirely on the subfloor. Self-levelling compound (or 'screed') is designed to flow into low spots and create a smooth, flat surface ready for tiles, laminate, or vinyl.

Our **self-levelling screed calculator** ensures you purchase exactly enough bags to achieve your target depth, preventing mid-project shortages that can cause 'cold joints' and an uneven finish.

Depth vs Bags (10m²)

3mm Depth~3 Bags (20kg)

5mm Depth~5 Bags (20kg)

10mm Depth~9 Bags (20kg)

Surface Preparation

Before pouring, the subfloor must be clean, dry, and free of any dust or grease. Any large cracks or holes should be filled with a rapid-set mortar first to prevent the expensive levelling liquid from leaking into the ceiling below or through the floor structure.

Always use a **spiked roller** immediately after pouring. This helps the liquid to flow together and, more importantly, releases any trapped air bubbles that would otherwise leave small craters in your finished floor.

Bag Sizes

Most UK retail and trade brands (like Mapei, Arditex, or Setcrete) sell compound in 20kg or 25kg bags. Our calculator provides estimates for both to match your chosen product.

Over UFH

When screeding over water-based underfloor heating, you usually need a minimum of 10mm coverage above the top of the pipes to prevent 'striping' and ensure even heat distribution.

Pro Tip: Mixing Speed

Use a mechanical mixer on a **slow speed**. Mixing too fast introduces excessive air into the compound, which can lead to bubbles and a weaker surface. Once mixed, pour immediately—levelling compound doesn't wait!

Floor Screed FAQ

Project Disclaimer

Screed requirements can vary significantly if the subfloor is very uneven. We always recommend purchasing one or two extra 'safety bags' above the calculated amount. Unopened bags can usually be returned for a refund.