Plastering, screed and drying out: how long to allow before the finishes

After first fix and insulation, the walls and floors are closed and finished. This stage adds a lot of water to the house in plaster and screed, and the house then needs time to dry before most finishes can go on. The common mistake is to treat drying as a gap in the programme to be squeezed. The cost of rushing it appears later as cracked plaster, lifting floors and mould.

What happens, in order

1. Plasterboard or wet plaster. Internal walls and ceilings are lined. With drylining, boards are fixed to studs or to dabs on masonry, with the joints taped and skimmed. With wet plaster, a base coat and a finish coat go directly on blockwork.
2. Airtightness check. In a masonry house the plaster is often the airtight layer, so it needs to be continuous behind and around sockets, pipes and the edges of floors. See insulation and airtightness.
3. Screed. The floor screed is laid over the insulation or slab, often with underfloor heating pipes in it. It is levelled and left to cure.
4. Drying out. The house is ventilated and later gently heated until the plaster and screed reach a moisture level the finishes can tolerate.
5. Protection. Floors are covered, and stairs, window sills and openings are protected from damage by the trades that follow.

Plaster: wet or dry

The choice also changes the order of work. Wet plaster needs the windows in and the roof on, and the electrics and plumbing first fix finished. Drylining on studs can go on earlier but needs the airtightness layer completed before the boards cover it.

Type	What it is	Watch for
Wet plaster	Layers of plaster applied directly to block or concrete	Water in the house, cracking in the first weeks, airtightness depends on the coat
Drylining	Plasterboard on dabs or studs, joints taped and skimmed	Gaps behind boards unless sealed, joint cracks, screws or dabs visible

Either can be well done. Ask your plasterer which they are using and why. For an airtight house, ask where the airtightness layer is and how penetrations and board edges are sealed.

Check the finished surface in raking light: hold a torch parallel to the wall and see ripples, ridges and dips. Mark them with tape for repair while the plasterer is on site.

Screed

Screed is a layer of sand-cement or a flowing liquid screed laid over the floor structure. It levels the floor and covers underfloor heating pipes.

• Thickness depends on the design and the heating system. Thicker screeds are slower to dry.
• Pressure test the heating pipes before the screed goes over them, and keep the test running if the supplier asks.
• Edge insulation strips at the walls let the screed move without cracking or bridging the wall.
• Curing. Cover the screed for the first days and keep traffic off it. Tell the other trades.
• Cracks. Fine shrinkage cracks can happen. Wider cracks or lifting edges should be shown to the screeder.

Drying out

Plaster and screed hold a lot of water, and the house will not dry on its own if it is closed up. Drying needs two things at once: air movement to carry the moisture out, and warmth to help it evaporate.

• Ventilate first. Open windows on dry days, or run the ventilation system on its drying setting, if the manufacturer allows it.
• Add warmth gradually. Heat the house slowly and steadily. Rapid heating can crack plaster and curl screed edges. With underfloor heating, follow the heating installer’s start-up schedule.
• Use dehumidifiers where the supplier or installer suggests them, with water collected and emptied.
• Check the progress. A moisture meter on the walls and a floor moisture test (such as a relative humidity test in the screed) tell you more than the calendar.
• Wait for the floor. Flooring suppliers specify the maximum moisture level for their products. Timber is usually the most demanding.

If you use temporary heaters, avoid unflued gas or paraffin heaters that put water vapour and fumes into the house. They add moisture and can be a fire risk. Ask your builder what they plan to use.

Who does what

A common source of conflict is that the plasterer finishes in a week while the drying takes a month. Put the drying period into the programme and the payment schedule so that nobody is pushed to lay floors early.

The plasterer and screeder work for the builder, or directly for you if you manage the build. The designer specifies the floor build-up, and the underfloor heating installer sets the heat-up schedule. The assigned certifier’s inspection plan may include a stage inspection before plastering, which is the last moment the hidden elements can be checked. If you are unsure whether a drying approach is safe for your build, ask the designer or the suppliers.

What to check and photograph

• The walls and ceilings before and after plastering, so that you know where the services are.
• Underfloor heating pipe layouts before the screed, with the pressure gauge.
• Screed thickness at several places (the screeder can show the depth at an opening).
• Edge strips in place.
• Any cracks, with a pencil mark and date to see if they grow.
• Moisture readings, noted with the date.

What goes wrong, and what it costs

Most drying problems come from the programme, not the materials: a flooring date was fixed before anyone knew the screed thickness, or the heating was not connected until after the plaster went on. Work backwards from the flooring delivery to find when the screed needs to go down.

• Flooring laid too soon. Timber cups, vinyl bubbles, adhesive fails. The cost is replacement and delay.
• Heating too fast. Cracked plaster, cracked screed and sometimes damaged pipes.
• Wet house in winter. Slow drying and condensation. Mould appears on cold surfaces.
• Poor airtight plaster. A failed air test, or draughts at skirting level.
• Damage by later trades. Paint on a floor with tools dragged across it. Ask for floor protection.
• No access to pipes. Services boxed in without a way to reach valves or manifolds.

Payments, site risks and cover

Plaster and screed may be separate payments in your builder’s schedule, and some lenders have an “internal finishes” or “plastered” stage. Check your offer. See staged drawdown explained and the stage payment planner.

Heaters, dehumidifiers and wet materials raise two risks: fire and water. Run temporary power safely, and check that the cover in place includes accidental damage and escape of water during the build. If you are heating an unoccupied house for weeks, someone should check it daily. See insurance when you project manage and the cover checker.

Before second fix

• You have a written note of any cracks, with dates, so that a later movement can be compared with what was there on handover.

• The flooring supplier has confirmed in writing the moisture level they accept, and your tester has recorded the reading against it.

• Plaster dry and sound, screed cured and tested.

• Moisture readings within the limits for the flooring you chose.

• Heating and ventilation commissioned or running as the installer instructs.

• The next stage: second fix and finishes.