Screed Moisture Testing: When and How to Test Before Laying Floor Finishes

Screed moisture testing is one of the most overlooked steps in any flooring project — and one of the most important. Laying floor finishes over screed that is too wet causes adhesive failure, bubbling, mould growth, and in severe cases, total floor failure requiring complete removal and replacement. This guide explains how moisture testing works and when it must be carried out.

Why Screed Moisture Testing Matters

All screed contains significant water during installation. As it cures, that water gradually evaporates. The screed looks and feels dry long before it actually is. A 50mm liquid screed may feel completely dry to the touch after two weeks, but still contain enough residual moisture to destroy a moisture-sensitive floor finish. Testing measures the actual moisture content rather than relying on appearance or touch.

The Two Main Testing Methods

Hygrometer test (RH): A plastic hood is taped to the screed surface and left for a minimum of 72 hours. A calibrated hygrometer measures the relative humidity of the trapped air. The industry threshold for most floor finishes is 75% RH or below. For anhydrite screeds, many adhesive manufacturers require 65% RH or below. Carbide bomb test (CM): A sample of screed is pulverised and combined with calcium carbide in a sealed vessel. The resulting gas pressure indicates the moisture content as a percentage. The threshold for most floor finishes is 2.5% CM for sand and cement and 0.5% CM for anhydrite screed.

When to Test

Always test before laying any moisture-sensitive floor finish including vinyl, LVT, engineered timber, parquet, carpet, and adhesive-fixed ceramic tiles. Test at the latest possible point before floor finish installation to allow maximum drying time. If the screed fails the moisture test, increase ventilation and allow more time — do not attempt to accelerate drying with direct heat, which causes surface cracking.

screeding.com provides drying guidance and aftercare notes with every completed project. If you have questions about screed moisture and floor readiness, ring us — we are happy to advise.