Floor screed in an apartment: when to pour it and how to check it

When the screed is poured

In the app route, the “Floor preparation and screed” stage comes after rough finishing: plastering brings water and debris, and once it's done it can no longer spoil the floor layers. After the screed comes waterproofing of wet areas, then ceilings, tiling and wall finishing.

Before pouring, everything that will end up inside or under the screed must be ready:

• pipes and cables the plumber and electrician laid across the floor;
• the floor drain or channel body - connected to the sewer and set at a height to suit the slope;
• water underfloor heating or a heating cable, if they go under the screed;
• floor sound insulation, if the design includes it.

If there will be no new screed and no underfloor heating under a screed either, the app survey will remove this stage from the route. An old screed is usually removed only if it's defective or the floor level changes.

What to do before pouring

1. Clean and dedust the base and check that it's sound: neither primer nor sound insulation will stick to a dusty base.
2. Prime and wait until it's completely dry - the drying time is on the packaging, don't shorten it.
3. Lay the sound insulation. A single rigid link between the screed and a wall cancels it out.
4. Check and protect the pipes and cables in the floor - fix them so they don't shift or get damaged during the pour.
5. Install the floor drain or channel body. The screed creates the slope to the drain, and afterwards the drain can't be moved.
6. Underfloor heating. Water heating - not under the bath or wardrobes, pressure-tested; in an apartment building, water heating from the shared heating or hot water system only with approval. Cable heating - not under the bath or wardrobes, the sensor in a conduit, resistance measured before and after laying.
7. Edge strip around the perimeter of every room: without it the screed will crack from thermal expansion.

What to photograph

Everything that goes into the screed is photographed before the pour: pipes, cables, underfloor heating, the drain. Photograph the whole room with a tape measure from the wall in the shot, and label the room. Separately - the sound insulation layers and the perimeter strip. A photo of the heating layout with a tape measure and the recorded cable resistance are required by the manufacturer's warranty.

Then the owner or designer checks the photos and the preparation - in the route this is the item “Accept the work before the screed is poured”. After the pour the pipes and cables can't be seen. More in Photos of hidden work.

Pouring and drying

The screed is poured along guide rails, allowing for the level of the finished floor covering in each room: tiles, laminate and boards need build-ups of different thickness. Work it out in advance, including adhesive and underlay, or there'll be a step where two coverings meet.

Screed takes weeks to gain strength - build that into the schedule. The app route gives drying guidelines:

• a semi-dry screed before waterproofing - 3-7 days;
• a wet one - from 14 days;
• before laminate and boards - about 28 days.

These are guidelines, not a guarantee: it all depends on the mix, the thickness and the weather. That's why the moisture is measured and the figure recorded before waterproofing and laying the covering. Don't speed up drying with heaters. Laying on a damp screed will ruin any covering.

How to check the screed

Take a 2 m straightedge, a level and a torch.

• Flatness. Lay the straightedge in different directions across the whole area. For a screed under piece materials laid on cement-sand mortar (tiles), the deviation from flat is no more than 4 mm under a 2 m straightedge (SP 29.13330.2011, cl. 8.13).
• Floor level. Compare with the finished floor level marked on the walls: the screed must reach the planned height in every room.
• Slope in wet areas. Where a lot of water reaches the floor, a slope is made: 0.5-1% for seamless coverings and tiled coverings (cl. 4.5). 1% is 1 cm per metre; in a shower without a tray the slope runs to the drain. Test with water: it should flow to the drain.
• Cracks and the edge strip. The strip is visible around the perimeter, the screed doesn't touch the walls rigidly.
• Moisture - measured and recorded.

The finished floor covering has stricter requirements than the screed: under laminate, parquet and linoleum the gap under a 2 m straightedge is no more than 2 mm, under tiles and stone no more than 4 mm (SP 29.13330.2011, cl. 5.18). If a screed for laminate came out with a 4 mm gap, the base will need further levelling.

These are Russian norms; other countries have their own. It's best to write base flatness requirements into the contract as well.

Stage acceptance checklist

• Pipes, cables, the drain and underfloor heating photographed and accepted before the pour.
• Edge strip around the whole perimeter.
• The screed is at the planned height in every room.
• Gaps under the straightedge are within what was agreed.
• There's a slope to the shower drain.
• Moisture measured before waterproofing.

How to track it in the Doma app

In the “Floor preparation and screed” stage the items go in the same order. The contractor attaches photos to the “Record the result” item and sends the work for review; you look at the photos and accept the item “Accept the work before the screed is poured”, and after the pour and the moisture measurement - the whole stage. The photos can later be found on the “Documents” tab → “Photo records”. The previous stage is Rough finishing, and how to accept work stage by stage in general is in How to accept a crew's work.