![]() Cohesion is when molecules that are the same cling to each other, for example a water droplet exists because the water molecules inside it stick together.Adhesion happens when particles that are not the same are attracted to each other, read more here.They are adhesion, cohesion and surface tension. There are three main forces at play in capillary action. A century later Irish chemist, Robert Boyle performed experiments to investigate it further. Leonardo da Vinci first observed and recorded capillary action in the late 15th century. The Science of capillary action explained in more detail Surface tension is produced by the proximity of the overlapping roof sheets driving the water upwards. This is due to the cohesive forces of the water molecules that are attracted to the opposing solid molecules of the steel roof sheet. Capillary action will now draw the water upwards into the tight space. In the diagram above you can see how water will flow downwards until it reaches the gap where the untreated roof sheets overlap. ![]() Accumulating moisture in a steel roof will eventually cause rust and leaks. With global temperatures increasing and climates becoming more humid, capillary action in untreated steel roofs will increase. However it decreases when temperatures are cooler. The process increases in warmer more humid environments. Water will always travel into a roof space by capillary action when its allowed. This is caused by the forces of adhesion, cohesion and surface tension. Water in tight spaces, such as the gap between steel roof sheets, will flow in any direction, even defying gravity. This is due to constant movement in the roof system caused by external weather conditions like wind, heat, the weight of water or the build-up of snow. Rubber or mastic seals are applied when the roof is first constructed in between the roof sheets, on each side of the fixings. Capillary action is sometimes referred to as capillary draw. What is Capillary Action in a Steel Roof?Ĭapillary action occurs on steel roof sheets when water travels in the narrow spaces (capillaries) between where they overlap. In this post we’re going to focus primarily on the affects of capillary action in steel roofs and cladding. Capillary action causes the water in the thinnest tube to rise to a higher level than it does in the wider tubes.
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