The Contractor’s Guide to Floor Levelling Compounds - Getting the Base Right
What are floor levelling compounds? They’re high-performance, polymer-blended cement liquids designed to correct uneven subfloors. Traditional concrete mixes are too thick for this job, and rigid; compounds use polymers to run fluidly across a space, filling low spots and featheredging down to nothing. The goal with floor levelling compounds is a perfectly smooth datum line that stops LVT from showing imperfections or engineered timber from bouncing underfoot.
Whatever your floor finish is there’s no room for error. Which is exactly why contractors and self-builders bring in Collie Floor Levelling. We won’t guess the water ratios or estimate the flatness. We treat subfloor preparation as a precise science, handling the tight curing windows and chemical bonding so your finished floor looks perfect, flat and stays anchored in the long term.
Floor Levelling Compound vs. Screed - What’s the Difference?
Confusing floor levelling compound with structural screed is a mistake you’ll want to avoid; you’ll either ruin your levels or go massively over budget. Screed is the heavy lifter that builds your structural depth and buries services, while compound is the precision finisher that gives you a flawless, workable surface.
Here is how the two layers divide the work on a project:
| Feature | Floor Levelling Compound | Sand and Cement / Flowing Screed |
| Primary Purpose | Final surface smoothing and minor tolerance correction. | Structural floor layer, floor-level raising, insulating. |
| Application Thickness | Typically 1mm to 15mm (specialist mixes up to 50mm). | Typically 35mm to 75mm+ dependent on type. |
| Aggregate Size | Fine silica sand and micro-aggregates. | Coarse sand, gravel, or large crushed aggregates. |
| Drying/Curing Time | Foot traffic in 2–4 hours; floor covering in 12–24 hours. | 1 day per mm of thickness (standard sand/cement). |
Can I use floor levelling compounds with any type of screed?
You shouldn’t assume that any compound can go over screed. If you pour a standard cement-based levelling compound over anhydrite flowing screed, they’ll react chemically while still wet. A crystal layer called ettringite will form right at the interface, which destroys the bond and causes the entire floor to delaminate and lift.
To prevent this, you need to mechanically sand off the shiny surface layer (laitance) of the anhydrite screed and seal it with a grit-primer to create a barrier before pouring.
Types of Self-Levelling Compound - Choosing the Right Mix for the Job
Don’t grab whatever bag is cheapest from the pallet and hope for the best. Different substrates require different chemistries. Pick the wrong mix, and the floor will either snap over timber or pull away from concrete. You need to match the product you choose to the structural challenge on site.
Here is how the main trade options break down:
1. Latex-Based (Two-Part) Compounds
You mix a bag of powder directly with a jug of liquid latex instead of water. These compounds deliver excellent bond strength and built-in elasticity. This should be your choice for unprimed concrete or spaces where you expect minor subfloor movement.
2. Water-Mix (Single-Part) Compounds
Just add clean water on site to activate the pre-blended dry polymers. These are highly fluid and very economical, making them the best choice for large-scale concrete or sand-and-cement screed projects where you need to watch the costs.
3. Fibre-Reinforced Compounds
These are packed with micro-fibres that create an internal mesh as the mix cures. They are what you need for timber floors, old tongue-and-groove boards, or floating screeds where slight structural or thermal movement would instantly crack a standard compound.
4. Deep-Fill / Deep-Base Compounds
Formulated with larger, specialised aggregates to allow heavy applications from 10mm up to 50mm in a single pour. They are engineered not to shrink, crack, or overheat when they’re poured in thick sections.
Application Window
A spiked roller is necessary for releasing trapped air bubbles and blending your pour lines, but there is a strict 10-to-15-minute operational limit. Once the polymers in the compound begin to cross-link, the material forms a delicate surface skin. If you run a spiked roller through it after that window closes, you will tear that skin, leaving permanent track marks and ridges that won’t disappear.
The Subfloor Selector - A Quick Trade Guide
Before you buy your floor levelling compound, run through the following checklist. You’ll see the most common floor types and the exact product combination you need to purchase to prevent delamination or surface failure.
- Working on Wood or Plywood? – Use a Fibre-Reinforced Flexible Compound. Standard rigid mixes will snap along the board joints.
- Burying Electric UFH Mats? – Choose a flexible, UFH-compatible Latex or single-part mix that’s designed to efficient heat transfer without cracking under temperature swings.
- Fixing major ruts or 40mm slopes? – Pour a coarse Deep-Fill Base Compound to level the structural gap without generating high exothermic heat, then use a standard compound for the final 2mm finish.
- Dealing with old bitumen or glue stains? – Get a Two-Part Latex Compound system. It offers good adhesion to difficult, non-porous surfaces where water-mixes fail to bond.
- Dealing with an Anhydrite Liquid Screed? – Do not pour directly. Sand the shiny laitance completely, seal the surface with a specialised grit-primer barrier, and then apply your levelling compound to avoid an ettringite reaction.
Get a No Risk Dead-Level Base
Getting a floor perfectly flat needs speed, exact water-to-powder ratios, and tight timing before the polymers skin over. Collie Floor Levelling focuses 100% of our daily operations on floor levelling applications. We secure the bond, eliminate pin-holes, and deliver a solid datum line that saves you site delays and material waste.
Get in touch with our trade specialists to book your pour – 01206 648 158
