Screeding questions

Screeding is priced per m² from your drawings: the area, the depth, the screed, access, the programme and what's included. Send the job and you get a written rate.

Area, depth and volume, screed type, labour and output, joints and preparation, access, the programme and what's done after the pour.

A 25 kg bag of sand and cement screed is about €11.90 without VAT, €14.64 with it.

Sand and cement: about a day per mm to 50 mm (BS 8204-1), 75 mm about 100 days. Liquid: 1 mm a day to 40 mm, then 2 days a mm.

Calcium sulphate from day 7; cement-based liquid screed from day 14 at no more than 45°C.

In a closed, heated building. A cement-based liquid screed is laid with the air inside between 5°C and 20°C.

Sand-and-cement is preferable for small extensions under 40 square metres, garage floors, wetrooms requiring steep falls to a linear drain, and staggered room-by-room renovations where a full-house pump setup is impractical.

Minimum depth depends on the build-up: 25 to 40 mm when slurry-bonded to a clean concrete slab, 50 mm when laid unbonded on a polythene membrane, 65 mm when floating on insulation boards, and 75 mm when covering underfloor heating pipes.

Under BS 8204 rules of thumb, traditional sand-and-cement dries at roughly 1 mm per day for the first 50 mm and 0.5 mm per day beyond that, meaning a 75 mm bed takes around 100 days in good drying conditions unless a rapid-drying binder or surface epoxy DPM is used.

SR2 is the standard domestic flatness class under BS 8204. When a 2 metre straightedge is rested anywhere on the cured floor, the gap beneath it must not exceed 5 mm. Microcement or thin commercial vinyl often needs SR1 (3 mm maximum gap).

Poor compaction in the lower half of the bed, insufficient water during mixing, soft building sand instead of washed 0/4 mm sharp sand, or frost and draughts drying the top crust before the cement hydrates are the main causes of friable, crumbly screed.

Ceramic and porcelain tiles can often be laid after 3 to 4 weeks using a flexible cementitious adhesive and decoupling mat, provided the underfloor heating has completed a full commissioning cycle and been turned off for 48 hours.