How to Fix Common Self Levelling Compound Mistakes

22/05/2025

Despite our best intentions, DIY doesn’t always go to plan! When resolving self-levelling mistakes, the good news is that there’s usually a reason for the problem and a way to fix it. Better yet, this article highlights exactly how to avoid these common self levelling compound errors, leaving you with the perfect even finish you’re looking for.

What Are the Common Mistakes with Self Levelling Compounds?

There are many common but avoidable mistakes when it comes to self-levelling. Our guide below highlights the main causes of self levelling issues, the concerns if left unresolved, and professional advice on fixing self levelling compound mistakes.

5 Common Mistakes When Applying Self Levelling Compound

1. An Uneven Finish

Why is it a problem?

Self levelling compound is designed to provide a smooth, flat, and even surface on which to lay flooring easily. If your compound layer is uneven, your flooring will be, too.

What causes it?

Uneven finishes often come down to poor preparation. If you haven’t thoroughly cleaned and hoovered the area, remaining dirt and dust will cause lumps and bumps in your compound. If you also fail to seal the edges correctly, your compound will seep out of your designated area, resulting in an uneven layer.

How to fix it?

Prioritise the subbase preparation stage, allowing more time if needed. Ensure the edges are sealed with expanding foam before applying the compound, and resolve any foundation issues. Self levelling compound naturally settles and levels itself, so help it along, let it flow, and then leave it to do its thing. This hands-off approach will also aid the use of a spiked roller, helping the compound find its level more effectively.

One of our most popular spiked rollers is the PREMTOOL spiked roller, perfect for smoothing out ripples after pouring and trowelling self levelling compound.

2. Poor Adhesion

Why is it a problem?

You may notice your compound taking longer to dry and cure, and in some cases, not drying evenly. This is because it hasn’t stuck to the subbase correctly, which will cause movement and weaken your compound and flooring.

What causes poor adhesion?

Poor adhesion of self levelling compound is caused by the primer you’re using. In many cases, you may be using the wrong primer for your type of compound, or not using primer at all, which ultimately means your compound won’t adhere to your subbase.

How to fix the issue?

Always use primer! It’s vital that you don’t skip this step, but it’s also important that you use the right primer for your type of self levelling compound. Look at the manufacturer’s recommendation for primer and follow their instructions for effective adhesion.

For example, when using Weberfloor Flex Flexible Fibre Reinforced Floor Screed, it is recommended by the manufacturers to use the Weber PR360 at 4:1 primer/water before application. Or, when using the Larsen SLC1550 Rapid Set Self Levelling Compound recommended to use the Larsen Acrylic Primer for best results.

3. Compound or Floor Cracking

Why is it a problem?

Self levelling is meant to create a smooth, flat surface to work on, with zero cracks. When cracks form, they weaken the structure and strength of your compound and shorten its durability. It can also impact the finish of your flooring and cause costly issues later.

What causes cracking?

Cracking is linked to poor subbase preparation. Failing to address foundation issues or fill existing cracks and gaps in your subbase will result in compound cracking. Cracks can also result from improper compound mixing, overwatering the mixture, or applying the self-levelling compound too thinly or too thickly. Always refer back to the manufacturer’s instructions.

The fix

Always check your subbase for cracks and gaps; ensure they’re filled, sanded and dry before applying your compound. A popular choice for filling cracks before laying self-levelling compound is the Ardex P 10 SR Repair Kit. It’s easy to use and is fast setting.

When mixing your compound, follow the manufacturer’s instructions and water ratios. It is highly recommended to use a paddle mixer for better consistency. The Bihui M14 Twist Mixing Paddle is a great choice; the gold zinc plated helps to make it more resistant to rust, extending the life expectancy.

Thin Compound

Why it’s a problem

Self levelling compound is designed to withstand high foot traffic. If the compound is too thin, it affects its structural integrity, potentially leading to cracks, uneven flooring, or bigger issues.

What causes it?

Thin compounds are caused by overwatering. This dilutes the self levelling mixture and weakens its structure. It can also be a result of spreading the mixture too thin across the area.

The fix

Following the manufacturer's guidelines will ensure you layer the appropriate self levelling thickness for your flooring. Typically, self levelling layers should be 5-15mm thick to aid drying and curing times and ensure even coverage. You can always apply another layer if needed.

Improper Curing

Why improper curing is a problem

If you fail to let yourself levelling compound fully dry and cure, you risk compromising its strength and durability. This can result in cracks, uneven surfaces, and problems when laying your flooring.

What causes it?

Improper curing is usually a result of poor time management or rushing a job. You’ve not allocated enough time for the compound to fully dry and harden. It can also be caused by exposure to high temperatures and moisture levels.

How to fix it

Patience! Curing is critical to the self levelling process and shouldn’t be rushed. Check the manufacturer's instructions, as each self levelling compound’s curing time will be based on temperature and humidity levels. Also, consider the size of the area and substrate, as this may take longer.

Premature Degradation

Why it’s a problem

When applied correctly, self levelling compound should last for years. Signs of premature degradation can impact the strength and capabilities of your flooring, resulting in cracked, weakened and uneven surfaces.

What causes premature degradation?

Although poor subbase preparation can cause premature degradation, a common cause is the use of an incorrect compound. For example, using an internal self levelling compound for an exterior patio, or using self levelling compound vertically on walls – self levelling is designed to work horizontally, making it ideal for flooring.

How to fix it

It’s important to use the right self levelling compound for your flooring project. This should include whether it’s internal self levelling compound or external self levelling compound, the type of subbase, and if there’s underfloor heating.

Tips to Avoid Self Levelling Mistakes

We’ve pulled together our top tips to help set you up for self levelling success:

Don’t skimp on proper subbase preparation
Choose the right compound for your subbase and follow the instructions
Don’t overmix or overwater the compound
Check temperature and moisture levels
Address cracks and gaps beforehand
Use the appropriate self levelling primer
If levelling over underfloor heating, allow for the minimum cure time before activation. Always refer to the manufacturer’s instructions
Use quality products and tools such as: trowels, mixers, levelling devices and moisture metres

Considerations and Best Practices

When it comes to avoiding self levelling mistakes, consider the location, weather conditions, and timeframe of your project to plan effectively. Also, remember key steps such as ground preparation and primer to ensure a professional finish.

We stock a wide range of self levelling tools, making sure you have all the tools you need for successfully laying SLC! From pin levellers and spiked rollers to flooring trowels, concrete grinders, vacuums and other floor preparation essentials.

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If you need help or advice when placing a self levelling compound order, please call 01604 859800 or email [email protected].