Floor Screed Types: Wet, Semi-Dry and Dry

How wet, semi-dry and dry screeds are built, the strengths and weaknesses of each, and which flat and floor finish each one suits.

Screed is the hidden layer of a floor that carries everything else. However good the parquet, tile or laminate, if the base underneath is uneven, cracked or not dry in time, trouble will eventually surface. Choosing the type of screed is not just a matter of the crew's habits: the load capacity of the building's slabs, the renovation schedule, underfloor heating and the final finish all bear directly on the decision.

What screed is for

Screed does several jobs at once. It evens out level differences in the structural slab, creates a solid, smooth base for the final finish, provides a layer for pipes and underfloor heating, and where needed covers a layer of sound or thermal insulation. Knowing which of these jobs matters most makes the choice of method easier.

Wet screed

This is the classic method: a mix of cement, sand and water is poured between screed rails and levelled with a straightedge. Reinforcing mesh is often added for strength.

Strengths:

• the technology is simple and widely known;
• laid correctly, it gives a strong, load-bearing base;
• it conducts heat well around underfloor heating pipes.

Weaknesses:

• the mix contains a lot of water, drying takes a long time and holds up the schedule;
• it is heavy, and a thick layer puts extra load on the slabs of older buildings;
• rapid or uneven drying brings a risk of cracking;
• the surface often needs additional levelling.

Semi-dry screed

Here less water goes into the mix and fibre is usually added to resist cracking. The mix is often prepared in a special machine and pumped through a hose, then the surface is levelled and power-floated.

Strengths:

• with less water, it dries faster than wet screed;
• the risk of shrinkage and cracking is lower;
• a power-floated surface often needs no extra layer under laminate or vinyl;
• pumping reduces mess and dust in the apartment.

Weaknesses:

• it requires equipment and an experienced crew;
• if the mix ratio is off, the surface can turn out weak;
• bringing in machinery is not always worthwhile for small areas.

Dry screed

A dry or prefabricated floor involves almost no wet process. A moisture barrier film is laid on the slab, graded expanded clay granules are poured and levelled on top, and then gypsum-fibre or similar boards are laid in two layers, bonded and screwed together.

Strengths:

• the next trade can start without waiting for drying;
• it is light, which suits older buildings and timber floors;
• it makes up large level differences without a heavy mix;
• it adds some sound and thermal insulation.

Weaknesses:

• in wet rooms it needs special waterproofing and strict adherence to the manufacturer's system;
• concentrated heavy loads, such as a heavy bath or a stone island, need additional calculation;
• if there is a leak, the fill absorbs water and part of the floor has to be taken up;
• combining it with water-based underfloor heating requires a dedicated solution.

Which one to choose

The choice follows from a few questions:

• How much extra load can the building's slabs take? A thick, heavy layer can be risky in an old building.
• How large is the level difference? For big differences, a thick wet layer is both heavy and slow to dry.
• How tight is the schedule? Dry and semi-dry methods shorten it.
• Will there be underfloor heating? Wet heating systems usually go with a cement-based screed.
• Which rooms are involved? Bathrooms and kitchens bring moisture risk into play.

Different solutions in different zones of one flat are possible, but layer heights must be calculated in advance so that no steps appear between rooms.

Whatever the method

Lay a compressible edge strip around the perimeter so the screed is separated from the walls and can expand. Screed rails should be set with a laser, and on underfloor heating or large areas movement joints should be cut according to the design. The finished screed must then be accepted for flatness and moisture before the final floor goes down.

Zaferoğlu İnşaat plans floor build-ups together with the final finish, underfloor heating and door heights on apartment and villa renovations. Unsure whether a wet, semi-dry or dry screed suits your flat? Ask us.