Why Is My Floor Levelling Compound Cracking or Pinholing?

Floor levelling and smoothing compounds are designed to create a smooth, even surface ready for a new floor covering. However, problems such as cracks, pinholes or an inconsistent surface finish can sometimes appear during or after application.

There isn't one single cause. Problems can relate to the condition of the subfloor, incorrect preparation, application depth, mixing or site conditions.

Here are some of the areas to check if your levelling compound isn't producing the finish you expected.

1. Was the Subfloor Prepared Correctly?

Good results start with the substrate.

Before applying a levelling compound, the background should be sufficiently dry and strong, while the surface needs to be clean, sound and free from contaminants that could affect adhesion.

Kelmore specifically identifies contaminants such as dust, dirt, oil, grease, laitance and curing agents as materials that need to be removed before its LevelMore products are applied.

Remaining adhesive residues should also be hard, sound, well adhered and not softened by water.

2. Did You Use the Correct Primer?

An absorbent subfloor can draw moisture from a levelling compound. Controlling the porosity of the background can therefore be important for the compound's workability and surface finish.

For example, Kelmore recommends PrimeMore Universal on concrete and cement:sand screeds before applying LevelMore Pro. Although Kelmore states that LevelMore Pro can bond to these porous backgrounds without priming, using PrimeMore Universal regulates the background porosity and improves adhesion, workability and surface finish.

Different substrates require different preparation, so don't assume that the same primer is suitable for every floor.

3. Was the Compound Mixed Correctly?

Always follow the exact mixing instructions for the product you're using.

For example, Kelmore LevelMore Pro is a two-part system. One 20kg bag of powder must be mixed with 4.5 litres of LevelMore Pro liquid.

Kelmore instructs installers to gradually add the powder to the liquid while mixing thoroughly with an electric paddle mixer until a smooth, lump-free consistency is achieved.

Using professional mixing equipment, such as a Collomix mixer and suitable paddle, can make it easier to achieve consistent mixing when preparing multiple units.

4. Could Trapped Air Be Causing Pinholes?

Air introduced during mixing and application can affect the final surface.

With LevelMore Pro, Kelmore advises that where the application thickness allows a spiked roller to move freely, using one while the compound is still wet can further enhance the surface finish by removing trapped air.

Correct preparation, mixing and application should therefore all be considered if pinholes are appearing.

5. Was the Compound Applied at the Correct Depth?

Every levelling compound has a specified application range.

Using a product outside its recommended depth can cause problems. Kelmore specifically warns that using a compound outside its recommended application range can lead to cracking and extended curing.

For example:

Kelmore Product	Application Depth
LevelMore Contract	2–12mm
LevelMore Pro	2–20mm
LevelMore Absolute 30	2–20mm
LevelMore Flow	2–25mm
LevelMore Rapid 30	2–30mm
LevelMore RenoFibre	2–40mm
LevelMore Flex&Fibre	2–75mm

Measure the deepest part of the floor before choosing your levelling compound rather than assuming one product will suit every application.

6. Were the Site Conditions Suitable?

Temperature and humidity can affect both working and drying times.

Kelmore states that higher temperatures and lower humidity shorten drying times, while lower temperatures and higher humidity extend them.

Cementitious products should also only be used when the air and background temperatures are 5°C or higher. At temperatures above 30°C, setting can accelerate significantly, making the product more difficult to work with.

How Can You Reduce the Risk of Problems?

Before levelling your next floor:

• Make sure the substrate is clean, sound and correctly prepared.
• Check whether the substrate requires priming.
• Select a compound suitable for the required application depth.
• Follow the exact mixing quantities stated by the manufacturer.
• Use appropriate mixing and application equipment.
• Work within the manufacturer's temperature requirements.
• Follow the specified working and drying times.

Final Thoughts

Cracking and pinholing shouldn't automatically be blamed on the levelling compound itself. Subfloor condition, porosity, preparation, mixing, application depth and site conditions can all influence the finished result.

Selecting the correct preparation system and following the manufacturer's technical guidance at every stage can help achieve a smoother, more consistent surface.

At Floormart, we stock the Kelmore LevelMore and PrimeMore ranges, alongside professional Collomix mixers, mixing paddles and floor preparation tools to help installers complete the full subfloor preparation process.