When Do You Need Leveling Compound?
Leveling compound is used when the floor substrate is not level enough for the planned covering. Unevenness, gradients or old adhesive residues must be leveled before tiles, laminate, vinyl or parquet can be installed.
Tolerances depend on the covering: tiles require levelness of max. 3mm deviation over 1m measuring length. Laminate and vinyl are more tolerant (max. 3mm over 2m) but react sensitively to point elevations. Carpet is most tolerant but shows unevenness most visibly.
Step 1: Check and Prepare the Substrate
Before applying leveling compound, the substrate must be clean, dry, load-bearing and free of loose parts. Old adhesive residues are removed mechanically (floor scraper). Loose areas are tapped and removed. Cracks are filled with repair mortar.
Measure residual moisture: Cement screed max. 2% CM (with underfloor heating max. 1.8%). Calcium sulfate screed max. 0.5% CM (with UFH max. 0.3%). Floors that are too moist cause blistering under the leveling compound.
Remove dust thoroughly: Best with an industrial vacuum cleaner. Residual dust prevents primer adhesion and thus leveling compound adhesion.
Step 2: Prime
The substrate must be primed before applying leveling compound. On cement screed and concrete, use deep primer; on calcium sulfate screed, a special CAF primer.
Apply deep primer evenly with a roller. On highly absorbent substrates, two passes: first diluted 1:1 with water, then undiluted. Drying time: at least 4 hours, preferably overnight.
On smooth substrates (e.g., old tiles), use bonding primer (quartz primer) instead of deep primer. The rough surface gives the leveling compound mechanical grip.
Step 3: Mix the Leveling Compound
Leveling compound is supplied as powder and mixed with water. The mixing ratio is on the packaging, typically 25 kg powder to 5.5-6.5 liters water.
Important: Always put water in the bucket first, then add powder. Never the reverse! Mix with a mixing paddle (on a drill) for at least 2 minutes until homogeneous. Let stand 2 minutes, then briefly remix.
Consistency should be thin-liquid, similar to pancake batter. Too thick = will not self-level. Too thin = sinks into pores and does not form a closed layer.
Step 4: Pour and Level
The compound is poured in strips onto the floor, starting at the wall opposite the door. Distribute evenly with a squeegee (leveling bar) or notched trowel.
Roll a spiked roller (deaeration roller) over the freshly applied compound. It removes air bubbles that would otherwise appear as craters in the surface. Roll in overlapping paths slowly across the entire area.
Maximum layer thickness per pass: 10mm. For larger irregularities, work in multiple layers, each after complete drying of the previous layer (24 hours for standard compound, 4 hours for fast-drying compound).
Step 5: Dry and Sand
Standard compound: Walkable after 4-6 hours, ready for covering after 24 hours. Fast-drying compound: Walkable after 2 hours, ready after 4 hours. Calcium sulfate compound: Walkable after 6-8 hours, ready after 48 hours.
After drying, check the surface with a scraper for nibs and irregularities. Sand individual high spots with sandpaper (80 grit). Vacuum up dust again.
Before installing the covering, check levelness with a 2-meter straightedge. Deviations over 3mm/m require further leveling.
Consumption Calculation: Formula and Example
The basic formula: Consumption (kg) = Area (sqm) x Thickness (mm) x Consumption per sqm per mm. Typical consumption values: Standard compound 1.5 kg/sqm/mm, fiber-reinforced 1.6 kg/sqm/mm, calcium sulfate 1.8 kg/sqm/mm.
Example: 20 sqm floor, average 5mm leveling, standard compound. Consumption: 20 x 5 x 1.5 = 150 kg = 6 bags of 25 kg. Water: 6 x 6 L = 36 liters. Cost: 6 bags at approx. 15 EUR = 90 EUR.
Tip: Measure the unevenness at multiple points and calculate with the average. Plan 10% reserve. For large areas over 30 sqm, a screed pump that applies the compound mechanically is worthwhile.