Why is there moisture on a sandwich panel wall?

Look beyond the most visible droplet. Water may run down from higher up or travel along the profile. Record the weather, heating and door positions. Observations under several conditions tell you more than a single visit to a dry building.

Keep a simple log of time, temperature, humidity, door positions and the location of the water. If a damp strip keeps appearing along one support, compare its temperature with the adjacent panel area. A regular pattern suggests local cooling but needs measurement to confirm it.

Condensation can occur when the surface falls below the dew point of the surrounding air. At 18°C and 70% relative humidity, the dew point is about 12.4°C. Steel at 11°C may then become wet. This illustrates the physics; it does not diagnose any particular wall.

Measure air temperature, relative humidity and surface temperature at the affected location. Allow for instrument accuracy. Non-contact readings on shiny metal can be misleading; if necessary, use a specialist who can account for the surface and its surroundings.

Washdown, wet goods, a new floor slab or a high occupancy can release moisture. Note when these sources are active and check ventilation capacity. Heating changes relative humidity but does not remove water: without air exchange or dehumidification, it stays in the building.

Temperature distribution matters. Warm, humid air from an adjoining room can reach a cold warehouse wall. Opening a large door can change conditions within moments. A distant sensor may not reflect what is happening at the facing.

Metal facings strongly resist vapour diffusion through the panel face. Joints and openings also determine enclosure performance: an air leak can carry moisture into a cold part of a joint. Trace the seals at panel joints, plinths, windows and service penetrations.

Do not add a membrane without assessing its position and how it joins existing layers. Vapour may move in a different direction in refrigerated buildings than in heated halls. The detail must suit actual temperatures and humidity on both sides.

If measurements indicate excessive indoor humidity, tackle the source and ventilation. For local cold spots, examine thermal bridges and insulation continuity. For rain ingress, check flashings, drainage and joint seals. Let the cause determine the order of work.

Assess the panel if water may have entered it. A sealed surface does not prove that the core is dry and sound. Determine how to deal with a damp area before covering it with a new facing. The repair should stop the cause and restore the entire detail.

After repair, repeat the measurements under comparable conditions. If the wall used to get wet during washdown, monitor a wash cycle. If droplets formed after cold nights, check after another cold night. A warm, dry day cannot establish success on its own.

Document the work and observations. Agree on operating temperature and humidity limits. Persistent symptoms may call for a hygrothermal analysis of the whole wall to assess the layers and conditions that a surface inspection cannot reveal.