Professional Guide

Best Self Levelling Compound for Uneven Floors: 2025 Expert Review

DR Joinery

Expert Joiner & Flooring Specialist

Published 16 December 2025

If there is one thing I have learnt working across York's historic properties, it is that nothing is ever truly square or level. Whether it is a Victorian terrace or a 1930s semi, the subfloor is rarely ready for hardwood flooring straight away.

Many homeowners make the mistake of thinking the underlay will hide the dips. It won't. If your subfloor isn't flat, your expensive new oak floor will bounce, creak, and eventually fail at the joints. The solution is often a high-quality self levelling compound.

In this review, I'm comparing three distinct options I keep in the van: a budget-friendly liquid additive for standard mixes, a deep-fill compound for significant drops, and a fibre-reinforced screed essential for timber substrates.

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Specs vs. The Real World

The Spec: "The Term 'Self Levelling'"

The Theory

"The marketing suggests you simply pour the liquid out and it naturally finds a perfectly flat water level on its own."

The Reality

In practice, these are 'self-smoothing' compounds. You absolutely need a trowel to guide it into the corners and a spiked roller to release trapped air bubbles. It requires a skilled hand to get truly level.

The Spec: "Walk on in 2 Hours"

The Theory

"The bag states it is fast-drying and ready for foot traffic in a couple of hours."

The Reality

Whilst you might be able to walk on it, it is certainly not ready for hardwood flooring installation that quickly. Timber needs a bone-dry substrate. Always check moisture levels with a hygrometer before laying wood on top.

My Top 3 Recommendations

Three options to cover different needs and budgets

Bond IT 5L Flooring Compound LevelMaster Acrylic Liquid Latex

Budget Pick

ARA CHOICE

This is slightly different from a bag of powder; it is a liquid latex additive designed to improve standard levelling compounds. If you are working on a budget and using a generic cement-based powder, adding this is crucial for flexibility and adhesion.

Price£9.49 (at time of writing)

TypeLiquid Latex Additive

Volume5 Litres

Use CaseImproves flexibility of standard mixes

The Good

Excellent value for improving cheaper compounds
Increases flexibility (vital for slight movement)
Improves adhesion to difficult substrates

The Bad

Requires a separate powder component (it's an additive)
Not a standalone levelling solution
Mixing ratios must be precise

Installer Tip:

Don't skip this if you're using a basic sand/cement screed or cheap powder. The latex adds the elasticity needed to prevent cracking when the house temperature changes. Mix it thoroughly with the powder until you get a smooth, lump-free batter.

Priced at £9.49 at the time of writing

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Bostik Cempolay Deep Self-Levelling Compound Grey - 20kg

Quality Pick

Bostik

When working in older York properties, we often find floors that have dropped significantly or have deep ruts. Standard compounds crack if applied too thick, but this Bostik 'Deep' formula can handle depths up to 50mm in a single pour.

Price£22.95 (at time of writing)

Depth Range5mm to 50mm

Setting TimeFoot traffic in 90 mins

SuitabilityConcrete, Screeds, Tiles

The Good

Can fill deep variances (up to 50mm) in one go
Fast setting times allow work to continue same-day
High strength finish suitable for heavy traffic

The Bad

More expensive per bag than standard options
Sets very quickly - you must work fast

Installer Tip:

Because this sets fast (90 minutes to walk on), organise your tools before you start mixing. Have your bucket, whisk, and trowel ready. Do not try to mix more than one bag at a time if you are working alone, or it will go off in the bucket before you can pour it.

Priced at £22.95 at the time of writing

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Nassboards - Larsen Fibre Reinforced Leveller 20kg

Problem-solving Pick

Nassboards

This is my go-to product for timber substrates. The 'fibre reinforced' aspect is critical; the tiny fibres act like steel rebar in concrete, holding the screed together even if the wooden subfloor moves slightly. It is expensive, but cheaper than re-doing a cracked floor.

Price£26.99 (at time of writing)

ReinforcementFibre strands for flexibility

Application Depth3mm to 50mm

SubstratesTimber, Concrete, UFH

The Good

Fibre reinforcement prevents cracking on flexible floors
Excellent flow properties for a smoother finish
Versatile depth range (3-50mm)

The Bad

Premium price point
Requires careful priming of timber floors first

Installer Tip:

When using this over floorboards, ensure all boards are screwed down tight (not nailed) to minimise movement. You MUST seal the gaps between boards with decorators caulk or tape first, otherwise, the liquid product will leak through to the ceiling below. Trust me, I've seen it happen.

Priced at £26.99 at the time of writing

Check Price on Amazon

Frequently Asked Questions

Can I use self levelling compound over floorboards?

Yes, but only if it is a 'flexible' or 'fibre-reinforced' compound like the Larsen product listed above. Standard concrete levellers will crack perpendicular to the floorboards as the wood expands and contracts. Always secure loose boards and seal gaps before pouring.

Do I need to prime the floor before levelling?

Absolutely. Priming is arguably more important than the compound itself. It seals the substrate so the water from the mix isn't sucked out too quickly (which causes cracking) and aids adhesion. Use an acrylic primer, never PVA, for flooring jobs.

How thick can I pour self levelling compound?

It depends on the product. Standard mixes are usually 3mm to 10mm. Deep-fill compounds like the Bostik Cempolay can go up to 50mm. If you need to raise the floor higher than that, you should be looking at constructing a timber subfloor or using a dry screed system.

Why did my self levelling compound crack?

Common reasons include: too much water in the mix (weakens the structure), drying too fast (draughts or direct sunlight), lack of primer, or movement in the subfloor. In York's older houses, draughts coming up through the floorboards are a major culprit for rapid drying cracks.

Do I need professional help for floor levelling?

For small utility rooms, a DIY approach works. However, for large open-plan areas or when preparing for expensive hardwood flooring, getting a professional is wise. At DR Joinery, we ensure the levels are laser-accurate to prevent issues with the final floor fit.

What tools do I need for self levelling?

You will need a mixing bucket (clean), a heavy-duty whisk/drill, a steel trowel for smoothing edges, and a spiked roller. The spiked roller is essential—it removes air bubbles and helps blend the mixes together for a seamless finish.

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