Freshly laid screed looks solid within a day or two, but looking dry and being dry are very different things. Lay flooring too soon and trapped moisture can lift tiles, cup timber and ruin adhesives. Here is what to actually expect, based on the screeds we lay in homes across Edinburgh, Fife and the Borders.
Most traditional sand and cement screeds can be walked on after 24 to 48 hours and take light site traffic after about a week. Full drying is much slower. The usual rule of thumb is 1mm of thickness per day for the first 40mm, then 2 days per millimetre after that. So a standard 65mm screed needs roughly 90 days to dry fully in good conditions, not the fortnight many people expect.
Anhydrite (calcium sulphate) flowing screeds, which we often use over underfloor heating, are walkable in 24 to 48 hours too, but they dry at a similar overall rate and are more sensitive to moisture, so they cannot be rushed either. Fast-drying modified screeds are the exception and can be ready for flooring in as little as 3 to 14 days, at a higher material cost.
Screed dries by moisture evaporating from the surface, so it depends entirely on the air around it. The drying rule assumes about 20C and 65 percent relative humidity. A damp autumn in Fife or a cold winter in the Borders rarely gives you that, and an unheated extension in January can take half as long again, sometimes double.
Good practice is to keep windows closed for the first week so the screed cures properly and does not dry too fast at the surface, then ventilate and gently heat the space afterwards. A dehumidifier makes a real difference from week two onwards. If the screed covers underfloor heating, the system should be commissioned slowly, typically raising the water temperature in stages from around day 7 for anhydrite or day 28 for sand and cement, which also helps drive out moisture.
The only reliable way to confirm a screed is dry is to test it, not to guess from the calendar. Flooring manufacturers generally require below 75 percent relative humidity (measured with a hygrometer box or probe) before laying vinyl, timber or carpet, and anhydrite screeds usually need 0.5 percent moisture or less by weight before tiling.
Ceramic tiles are slightly more forgiving on cement screeds because they breathe a little, but wood and vinyl are not. If a floor fitter or tiler asks for a moisture test result before starting, that is a good sign, not an obstruction. Anhydrite screeds also need the surface laitance sanded off before tiling, which is best done between 7 and 10 days after laying.
The most common problem we see is a renovation programme that allows two weeks between screeding and flooring when the screed genuinely needs two months. If your timescale is tight, tell your screeder before the pour. Options include a thinner screed where the build-up allows, a fast-drying additive, or a proprietary rapid screed, each of which trades cost against time.
On a typical extension or renovation in this part of Scotland, we would suggest screeding as early in the build as possible so it dries while other trades work elsewhere, keeping some background heat on through winter, and booking a moisture test a week before flooring is due. That small amount of planning avoids the expensive job of lifting a failed floor.