Self-Levelling Compound: Where and How

Self-levelling compound does not replace screed; it finishes it for the final floor. When it is needed, how it is applied and where people go wrong.

However carefully screed is laid, its surface can still show waves, small hollows and marks left by screed rails. Ceramic tiles absorb such defects to some extent in the adhesive bed, but vinyl, linoleum, thin laminate and glued parquet reveal every bump underneath. Self-levelling compound was made for exactly this situation: it is very fluid, spreads by itself and gives a smooth, flat finished surface.

How it differs from screed

Despite its name, self-levelling compound is not a magic material that straightens a crooked floor on its own. Its job is to take a base that is already roughly flat to the level the final floor covering demands.

Screed handles large level differences, is laid in a thick layer and is levelled with rails and a straightedge.
Self-levelling compound is applied in a thin layer and smooths the surface thanks to its flow, but it is not designed to make up large differences.

Each product states its minimum and maximum layer thickness on the packaging. Going outside these limits leads to cracking, the layer detaching from the base or a weak surface. If the difference is large, correction is made at screed level first.

Types

Most compounds are based on cement or gypsum binders.

Cement-based compounds resist moisture, and there are versions suitable for kitchens, bathrooms and underfloor heating.
Gypsum-based compounds flow well and shrink little, but they are for dry rooms and are not used in wet areas.
Rapid-drying and fibre-reinforced special compounds are used when the schedule is tight or on difficult substrates such as timber.

When choosing, check which final coverings the product is intended for, whether it is compatible with underfloor heating, and when it can be walked on.

Preparing the base is half the job

Self-levelling compound cannot be stronger than the layer beneath it. If preparation is skipped, even the best material can blister or crack.

The base must be sound: crumbling, dusting or hollow-sounding areas are removed and repaired.
The surface is cleaned of oil, paint, adhesive residue and dust, ideally with an industrial vacuum.
Deep cracks and holes are filled beforehand with a suitable repair mortar.
An edge strip is fixed along the walls so the compound does not bond directly to them.
Door thresholds and pipe penetrations are temporarily sealed so the compound does not run away.

Primer is not optional

Pouring without primer is the most common mistake. A dry, porous base draws water out of the compound quickly. The compound then stiffens too soon, does not flow properly, air bubbles appear on the surface and the layer cures weakly. Primer controls the absorbency of the base and improves adhesion. Its type depends on the substrate: a porous cement base needs one primer, a dense or smooth surface may need another. The compound should be poured only after the primer has dried for the time the manufacturer specifies.

Application sequence

1. Measure the water precisely. Extra water added by eye makes the mix flow more easily but lowers surface strength and causes segregation.

2. Mix with a paddle mixer until there are no lumps, let it stand briefly and mix again.

3. Pour in strips from the far corner of the room towards the door. Each strip is poured while the previous one is still fluid, so no joint lines remain.

4. Spread the thickness evenly with a gauge rake or notched trowel.

5. Go over the surface with a spiked roller to release trapped air. The installer walks on spiked shoes.

The working time of the mix is short, so on larger areas two people and materials prepared in advance are essential.

Drying and typical mistakes

After pouring, the room should have no draughts, direct sunlight or heaters. A surface that dries too fast cracks. The time until you can walk on it and the time until the final covering can go down are different. The second depends on thickness and conditions and is confirmed by measuring moisture.

The most frequent mistakes are:

trying to fill a large screed deviation with self-levelling compound;
pouring without primer;
adding more water than the instructions allow;
mixing in small batches with long breaks in between;
using a gypsum-based compound in a wet area.

Zaferoğlu İnşaat plans floor build-ups in kitchens, dining areas and other rooms according to the demands of the final covering. We are glad to discuss floor preparation in your home at our office.

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