Screed vs. self-leveling compound: which one you need
By Michał Białas · Last updated
Self-leveling compound is for thin layers, from about 1/8 in to roughly 1 in (3–30 mm, depending on the product), over a floor that is close to right. Screed (sand-cement or liquid screed) is for thick layers and big height differences. When the floor is far out of level and the finish needs a smooth surface, the usual answer is both: screed to take up the slope, then a thin self-leveler skim on top.
What each product does
| Self-leveling compound | Sand-cement screed | Liquid (anhydrite) screed | |
|---|---|---|---|
| Typical layer | About 1/8–1 in (3–30 mm) | About 1–4 in (25–100 mm) | About 1 1/4–3 in (30–80 mm) |
| Typical use | Smoothing, small dips, under vinyl and large tile | New floors, deep slopes, floating floors, radiant heat | Large areas, radiant heat, fast placing |
| Sold as | Bags, about 50 lb / 25 kg | Bags of sand mix, or cement and sand | Ready-mix, delivered by volume |
| Coverage | About 1.6 kg/m² per mm | About 2.0 kg/m² per mm | About 2.0 kg/m² per mm |
| Surface | Smooth, ready for most finishes | Rougher; may need a skim for vinyl | Smooth; needs laitance removed |
Values are typical. The minimum and maximum thickness of your product are on its data sheet, and the calculator warns when your numbers fall outside them.
When self-leveler alone is enough
Use self-leveler alone when the floor is basically sound and the height difference is within the product’s maximum thickness. It is the standard fix under click vinyl, glue-down vinyl and large-format tile, which all need a flat, smooth surface. It flows out on its own, so you pour it, spread it with a gauge rake and roll it with a spiked roller to release air.
Example 1 (feet): 12 × 10 ft room, 1/4 in of self-leveler
- 120 sq ft = 11.15 m²; 1/4 in = 6.35 mm.
- 11.15 m² × 6.35 mm × 1.6 kg/m²/mm × 1.05 waste = 118.9 kg = 262 lb.
- Bags: 262 ÷ 50 = 5.2 → 6 bags of 50 lb.
- Primer underneath: 0.46 L of concentrate → 1 quart.
When you need screed
Use screed when the layer gets thick: deep slopes, building up a floor to meet another room, covering radiant heating pipes, or a floating floor over insulation. Self-leveler in thick layers is expensive, and above its maximum thickness it can crack or fail to cure properly. Sand-cement screed is much cheaper per inch of thickness, but it takes longer to dry and its surface is rougher.
The calculator warns when the deepest point exceeds the product maximum, and suggests a two-layer build-up when the height difference is more than about 2 in (50 mm) under self-leveler.
Two layers: screed plus a self-leveler skim
The screed takes up the slope and the bulk of the thickness; the self-leveler layer, often only about 1/8 in (3 mm), gives the smooth, flat surface. In the floor renovation calculator this is the “self-leveling layer on top of the screed” switch under the screed card. It adds the leveler and its own primer.
Example 2 (meters): 5.0 × 4.0 m floor sloping 60 mm
- Self-leveler alone (3 mm minimum at the high point, even slope): average 33 mm, deepest 63 mm — over a typical 30 mm maximum. 1,108.8 kg → 45 bags of 25 kg.
- Two layers instead: bonded sand-cement screed, 25 mm minimum, average 55 mm → 2,310 kg → 93 bags of 25 kg.
- Plus a 3 mm self-leveler skim: 20 m² × 3 × 1.6 × 1.05 = 100.8 kg → 5 bags.
- Plus primer before each layer: 0.825 L each → 1 × 1 L each.
- More bags in total, but sand-cement typically costs a fraction of leveler per bag, and both layers stay within their thickness limits.
Example 3 (feet): 15 × 12 ft floor sloping 2 1/2 in
- Bonded sand mix, 1 in minimum, even slope: average 2 1/4 in → 4,425 lb → 56 bags of 80 lb.
- Self-leveler skim of about 1/8 in on top: 186 lb → 4 bags of 50 lb.
- One quart of primer before the screed and one before the leveler.
Decision checklist
- Measure the height difference (see how to check if a floor is level).
- Check the finish: vinyl and large tile need a smooth surface; laminate and small tile tolerate more.
- If the deepest point fits within the leveler’s maximum, use leveler alone.
- If not, screed the slope first and plan a leveler skim if the finish needs a smooth surface.
- Check the weight: about 2 in of sand-cement screed weighs roughly 20 lb per sq ft (100 kg/m²). On wood floors and upper stories, ask whether the structure can take it.
- Plan drying time before the finish goes down (see screed drying time).
Frequently asked questions
Can I pour self-leveler 2 inches thick?
Only if the product says so. Most standard levelers stop at about 1 in (30 mm), some deep-pour products go further. Above the limit, use screed first.
Is self-leveler stronger than screed?
Not necessarily. They are made for different jobs. Self-leveler gives a smooth, flat surface in thin layers; screed builds height and strength in thick ones.
Do I need primer for both layers?
Usually yes. Bonded screed needs a bonding primer or slurry on the slab, and self-leveler needs primer on the screed to control suction and prevent pinholes.
Which dries faster?
Self-leveler: most are walkable after about a day and ready for finishes in days. Sand-cement screed often needs weeks, roughly a day per millimeter for the first 40 mm.