[Expert advice] Using PU foam sealant in winter conditions

Problems that come up when PU foam sealant is used in winter, what causes them and how to deal with them

The foam does not come out of the can, or it comes out but does not expand and stays liquid

Causes

1. The can valve is faulty. In this case the can has to be replaced.
2. The can is too cold. The propellant inside it has cooled below its boiling point and no longer builds enough pressure. Excessive cooling can also freeze the prepolymer in the can. To bring the can up to temperature, move it into a heated room or put it in warm water. Never heat a can with a heat gun or an open flame — this may cause an explosion.
3. The gun has no pre-chamber and the bore of its barrel is too narrow. This is typical of low-quality guns. The foam then cools very quickly as it passes through the gun and leaves the nozzle too cold, even when the can itself is within the allowed temperature range. The best answer here is to replace the gun with a better one. You can also try to insulate the barrel. If that is not possible, warm the can up as described above so that the foam does not have time to cool below the critical temperature on its way out.
4. The foam itself is of poor quality. Such foam behaves the same way in a heated room.

The can does not empty completely

Causes

1. Propellant pressure in the can is too low. The pressure may have dropped because a leaking valve has gradually bled off part of the propellant, or because the can is too cold. In the second case, warming the can up solves the problem.
2. A clot inside the can has blocked the valve. Clots form either because of a manufacturing defect or because the can was stored or handled at too low a temperature.

The foam does not expand after it leaves the can

Causes

1. The ambient temperature is too low. Check that the air temperature is within the limits printed on the can. A conscientious manufacturer always prints accurate figures there.
2. The can is too cold. Here it is enough to warm the can up in a heated room or in warm water.
3. The can was not shaken enough before use. The liquid components have not mixed properly with each other and with the propellant, so once out of the can they do not react as they should. Shake the can thoroughly again.
4. Air humidity is too low. The chemical reaction in PU foam sealant needs a certain amount of moisture, and frosty air may not hold enough of it. In this case the opening must be misted with water before the foam is applied, and the joint again immediately after. So that the water does not freeze in the opening and get in the way of proper adhesion of the foam to the surface, mist the sides in small sections and fill each section with foam right away.
5. Poor foam quality or a defective can.

The foam sags or falls out of the installation joint

1. The can is overheated. The propellant, now quite hot, boils as it leaves the can and expands the foam very effectively. But the gas cools quickly, its pressure drops sharply, the foam collapses at once and can no longer hold in the gap. A can that is too warm is therefore just as harmful as one that is too cold. To keep the foam from falling out of the gap because of an overheated can, use the table that matches the can temperature to the ambient temperature. The table was developed for KUDO^® PU foam sealants.

1. A strong draft through the installation gap in windy weather blows the foam out. The joint then has to be shielded from the wind, at least until the foam starts to set and gains its initial strength