Floor Levelling (up to 2.9 cm thickness)

Levelling compound evens out smaller irregularities. Depending on the product, it goes on in a layer from a few millimetres up to roughly three centimetres. The manufacturer states the exact thickness range on the bag, and you should stay within it.

Some problems are beyond a levelling compound. If the height differences are larger, the subfloor crumbles, has sunk, or is cracked deep down, the screed needs repairing first with a repair mortar, or a new, thicker screed has to go down. The compound is only as strong as what lies beneath it. If the base breaks up, the compound will come away with it.

Why does a level surface matter so much? Thin, rigid coverings, especially vinyl and laminate, show every little bump on the surface. When low sunlight comes through the window, dips become visible. A floating floor flexes over them, and over time the joints get damaged.

• Cement-based compounds are the all-rounders. They suit concrete and sand and cement screeds, and you can use them in bathrooms, kitchens and utility rooms.
• Gypsum-based (anhydrite) compounds flow very well and give a very smooth finish. They belong in dry rooms such as living rooms and bedrooms. They are not suitable for bathrooms or laundry rooms.
• Rapid-setting compounds shorten the wait before the floor covering can go down. They are useful when time is tight, for example when you are renovating a flat you are still living in.
• Compounds suitable for underfloor heating cope better with changes in temperature. A thin layer warms up quickly, so the heating responds faster.

The compound has to match the subfloor. On an anhydrite screed, use a compound and primer that the manufacturer explicitly approves for anhydrite. If you are unsure what your subfloor is, a floor layer can check it on site and decide.

The pour itself is quick. Most of the time goes into preparation, and the preparation decides whether the compound lasts.

1. Assessing the subfloor: the floor layer checks strength, cracks, hollow spots and moisture. A damp screed is a common cause of later problems. Both the compound and the floor covering manufacturer state the permitted moisture level. For anhydrite, the limit is much stricter than for cement.
2. Removing old layers: leftover adhesive, paint, bitumen and tar-based layers are ground or scarified off down to a sound base. If you want to reuse old parquet, it is worth taking it up carefully.
3. Local repairs: deep holes and broken patches are filled with repair mortar, and cracks are treated.
4. Vacuuming and priming: the surface is vacuumed thoroughly and coated with a primer suited to the subfloor. Primer evens out how absorbent the surface is and improves adhesion.
5. Edge strip: a foam strip goes round the edge of the room and around pipes. It keeps the compound separate from the walls and takes up movement in the material.
6. Mixing: the powder is mixed with the exact amount of water using a slow-speed paddle mixer until there are no lumps.
7. Pouring and spreading: work starts in the corner furthest from the door and moves towards it in strips about a metre wide. The mix is spread with a gauge rake or spreader, and each strip is joined to the last while both are still liquid.
8. De-aerating: a spiked roller is run over the fresh layer to release air bubbles.
9. Curing: the room is kept at a steady temperature, usually somewhere around 15 to 25 °C, with no draughts and no direct sunlight.

• Condition of the subfloor: clean, sound concrete only needs vacuuming and priming. Thick layers of old adhesive, tar or bitumen mean grinding or scarifying and a lot of dust.
• Shape of the room: a large, simple area can be poured in one smooth run. Small rooms with lots of corners, alcoves and doorways slow the work down.
• Layer thickness: where height differences are bigger, the compound is sometimes poured in two layers, with a waiting time in between.
• Type of mix: rapid-setting and specialist compounds give you less time to work, so the team has to be quicker.
• Access: on an upper floor with no lift, carrying bags and water takes longer. In a block of flats, plan noisy grinding around the building rules. The building management or owners' association can tell you what applies.

In older houses and flats, old vinyl tiles, adhesives or black tar-based layers can contain asbestos or harmful tar compounds. If you suspect this, do not grind them yourself. Have the material tested first. Only a contractor licensed for asbestos work may remove it.

You can handle a small room with a sound, dry subfloor yourself. For a larger area, get a helper: one person mixes while the other pours and spreads.

1. Read the technical data sheets for the compound and the primer, including the layer thickness and working time.
2. Remove leftover old floor covering and adhesive, then vacuum the subfloor.
3. Fill larger holes and cracks with repair mortar beforehand.
4. Apply the primer and let it dry as the manufacturer specifies.
5. Fix the edge strip around the whole room and around pipes.
6. Get buckets, a paddle mixer, a spreader, a spiked roller, a measuring jug for the water and spiked shoes ready.
7. Tape off the threshold and door so the mix cannot run into the next room.
8. Mix the compound with the exact amount of water until there are no lumps.
9. Pour in strips from the furthest corner towards the door and spread with the spreader.
10. Go over the surface with the spiked roller in both directions.
11. Close the windows, let the compound cure without draughts and stay off it until the manufacturer says it can be walked on.

• Missing or wrong primer: the subfloor draws water out of the compound, which then bonds poorly, cracks and may start to peel.
• Inaccurate water dosing: a mix that is too runny loses strength and can separate on the surface. A mix that is too thick will not flow out.
• No de-aerating: once the compound hardens, small pinholes are left on the surface.
• Layer too thick: an overly thick layer dries unevenly and can crack.
• Gaps in the edge strip: cracks then appear in the corners and around pipes.
• Laying the floor too soon: a covering laid on damp compound can warp, and adhesive does not hold well. Before laying wood or vinyl flooring, it is sensible to have the moisture measured.

• The surface is level, with no visible gaps under a long straightedge
• There are no cracks, pinholes or sharp ridges between the strips
• Tapping the floor gives no hollow sound anywhere
• The surface does not crumble or dust when you scratch it with a key
• The edge strip runs unbroken round the whole room, and the part that sticks up is trimmed only when the floor covering is laid
• The height works with thresholds and doors once the planned floor covering is added
• Before a sensitive covering goes down, the surface is lightly sanded and vacuumed
• The moisture level of the subfloor meets the floor covering manufacturer's requirements