Excess moisture in warehouse slabs can lead to serious problems; from coating failure and surface blistering to frost damage, joint movement, and long-term slab degradation. Whether you're pouring a new slab or finishing an existing one, controlling moisture is essential for durability and safety.
This guide explains the key methods for moisture management in concrete slabs, including prevention during construction, testing before finishes, and long-term control in operational warehouses.
For ground-bearing slabs, a high-performance vapour barrier (typically 1200 gauge DPM or higher) must be placed beneath the insulation or directly under the concrete. This prevents rising moisture from the subgrade migrating into the slab. Joints and overlaps should be taped or welded to form a continuous seal. Vapour barriers are critical in any warehouse where finishes like polish or resin are applied; they protect against blistering, bubbling, and long-term humidity issues.
Concrete slabs retain significant moisture after pouring. Even once they look dry, internal moisture can remain for weeks. A typical 150–200 mm slab requires at least 28 days to cure, but full drying can take 2–3 months depending on temperature and humidity. Applying coatings or polish too early can trap moisture below the surface, causing delamination or cloudy finishes. Always test moisture levels before applying any sealer or coating system.
Moisture testing is the only reliable way to know if a slab is ready for finish work. Relative Humidity (RH) probes inserted into the slab give a percentage reading; anything below 75% RH is usually acceptable for coatings. Calcium carbide (CM) testing is faster and also widely accepted. Don’t rely on surface dryness alone; deep moisture can still cause problems. Test multiple locations, especially in thicker or slow-drying sections of the floor.
Some coating systems seal the surface completely, locking moisture into the slab. If that moisture builds up under pressure, it can cause bubbling, peeling, or blistering. In older or moisture-prone slabs, consider breathable finishes like polished concrete or low-perm primers. If a high-build resin is required, apply a moisture-tolerant primer or surface DPM first to control migration. Always match the finish to the slab’s moisture condition.
Moisture doesn’t just come from below; surface water from cleaning, spills, or condensation can enter through damaged joints or cracks. Make sure all slab joints are sealed with flexible, waterproof joint fillers. In cold storage or damp environments, this prevents water ingress and microbial growth. Periodically inspect joints for shrinkage, cracking, or movement and reseal as required.
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