WORKING WITH SEALANTS IN COLD AND DAMP

Air temperature is not enough. On concrete, metal, stone, façade panels, external joinery and shaded façades in particular, the surface temperature can differ from the air.

If you apply silicone or PU over that layer, the sealant bonds to the moisture, not to the substrate. The joint can look perfect on the day and start debonding later.

The dew point is the temperature at which moisture in the air starts to condense on a surface. The higher the relative humidity, the closer it sits to the air temperature.

If the margin is smaller, do not rely on the surface looking dry. Wait for conditions to improve. This matters most with:

• early-morning work
• fog
• high humidity
• metal surfaces
• work after rain
• the evening temperature drop

The substrate must be clean, dry and free of ice, frost and condensation. Do not apply sealant to a frozen surface.

And do not assume wiping the condensation off solves it. If the substrate is still at or below the dew point, the moisture simply comes back.

In cold weather think about three separate temperatures — all three matter.

For many standard silicone and PU sealants the minimum application temperature is around +5 °C. That is not a universal rule — some products are designed for lower temperatures and others carry different limits.

So always check the data sheet for the minimum air temperature, the minimum substrate temperature and the temperature of the product itself.

Cold sealant becomes more viscous. That means:

• it extrudes with more difficulty
• it needs more force on the gun
• it is harder to tool
• it fills the joint less readily
• application can end up uneven

So in winter store cartridges within the conditions the manufacturer states. Do not leave them overnight in a cold vehicle, on a concrete floor, in an unheated container or outside on site.

If the product has gone cold, let it come up to a suitable working temperature gradually before use.

Do not try to compensate for a cold cartridge with:

• a torch
• a heat gun
• sitting it on a radiator
• very hot water
• any other uncontrolled heat source

Excessive heating can change how the material behaves and take it outside the permitted temperature range.

One-component silicones and many PU sealants cure by reacting with airborne moisture. The cure travels from the surface towards the inside of the joint.

Typical data-sheet figures are usually given at standard laboratory conditions, for example +23 °C and 50% relative humidity. On a winter site conditions can be entirely different — lower temperatures generally slow the cure, and in cold, dry air the difference can be substantial.

So do not automatically apply the summer schedule to:

• loading the joint
• overpainting
• contact with water
• fitting subsequent elements
• removing temporary propping

Check the actual conditions and the technical requirements of the product.

This matters most in winter. After a while the surface can look dry while the material deeper in the joint is still uncured.

Do not start external sealing if:

• it is raining
• the substrate is wet
• rain is imminent
• there is heavy fog or condensation
• there is no way to protect the fresh joint

But do not rely on a blanket rule such as at least six hours without rain. Different sealants skin over and reach water resistance at different rates.

On façade work a temporary canopy or sheet can shield the joint from rain, snow and direct wetting. But make sure the covering does not:

• touch the fresh sealant
• trap condensation on the joint
• block the air exchange the cure needs
• cause local overheating where heaters are used

The aim is a dry, controlled working zone — not just polythene laid over the bead.

Metal profiles and façade elements react very quickly to temperature change. They can:

• cool sharply overnight
• stay cold into the morning
• form condensation far more readily
• heat up fast in direct sun

With metal, measuring the surface temperature itself is therefore especially important. Dry air does not automatically mean dry metal.

One reading at 08:00 is not enough to run the whole day on. Conditions change — especially:

• in the morning
• moving from sun into shade
• with an approaching front
• in fog
• in the late afternoon
• when the temperature drops sharply

If humidity rises or the substrate cools, you can reach the dew point without a drop of rain. On long external runs, check the conditions periodically.