Maintenance and repair
How to find and repair the cause of a leak in a metal roof
In brief
Before sealing a metal roof, find out where water actually gets under the covering – the drip may show up well away from that point. Check drainage, flashings and roof penetrations, and the underside of the roof if you can reach it. Weather can mislead: a leak that shows up in windy conditions has a different cause from a stain during a thaw. Also consider condensation. Only then choose a material to suit the coating and joint type.
Why must the cause be found first?
A visible drip may emerge far from the point where water entered beneath the covering. Before repair, the path of runoff, the flashings and the penetrations through the roof surface are checked. Weather matters too. A leak that appears in wind may have a different cause from a stain that forms during a thaw.
The inspection should include the underside of the roof if it is accessible. It is worth checking whether the moisture comes from condensation. Sealing the external laps will not repair a leaky layer on the inside. In such a case, an analysis of the layer build-up and ventilation is needed, not another product applied to the steel sheet.
When can sealant be used?
A sealant makes sense in a detail intended for such a solution, on a stable and suitably prepared substrate. It should be compatible with the coating, resistant to external conditions and able to perform in the given joint. The information “for roofs” alone does not confirm suitability for every steel sheet and every location.
The requirements for temperature, substrate moisture and curing time must be checked. Applying the compound onto water, dirt or loose rust usually weakens adhesion. A thick barrier should not be formed across the drainage path. The seal is meant to close the actual gap, not create a new pocket for water.
What are sealing tapes used for?
Tapes are used, among other things, in specific laps and connection details. They may have a different construction, width and method of adhesive activation. Their position relative to the fixing and the direction of water flow is important. A tape pressed into a random gap does not automatically become a durable repair.
On an exposed surface, solar radiation and temperature changes must be taken into account. Not every material intended for an internal lap is suitable for leaving on top. The possibility of later removal should also be assessed. A wide adhesive strip may hide corrosion and make it harder to replace the actual component.
How is the area around a screw repaired?
First, the condition of the screw, the seal and the substrate is checked. An over-tightened washer may be deformed, and a loose fastener will not provide a seal. Tightening alone does not always help. If the hole is damaged or the support weakened, an appropriately selected repair method is needed.
A replacement fastener must match the support material and the load conditions. It should not be selected solely on the basis of a larger diameter. It is worth checking the adjacent fixings at the same time, but without blindly tightening the entire roof. A correctly functioning seal is not improved by compressing it to the maximum.
When does a flashing or sheet need to be replaced?
Replacement is sometimes necessary in the case of perforation, extensive corrosion, cracking or permanent deformation. The same applies when a flashing has the wrong shape and directs water under the covering. A sealant may temporarily limit the symptom, but it will not change the geometry. It is worth removing the cause before moisture damages further layers.
The new element must work with the old profile and coating. With tile-effect metal roofing, the height of the pressing and the module length matter. A similar colour does not mean the sheets are compatible. Before ordering, the actual dimensions and the method of connection must be established so that the repair does not create another weak point.
How should the surface be prepared for repair?
Contamination and loose fragments are removed in accordance with the requirements of the selected system. The coating should not be sanded or treated with solvent without checking that it is approved. It is worth assessing the adhesion of the preparation on a small area. The work should be carried out under conditions that allow the material to cure properly.
Access to the repair location must be safe. Wet steel sheet is not a suitable place for do-it-yourself experiments. Temporary protection may be needed before the actual repair, but it should have a clearly defined purpose and replacement date. A makeshift patch should not be presented as a permanent solution.
How can the result be checked?
Record the type of repair and take photos of the prepared detail. Observe the location during subsequent rainfall, especially similar to that which previously caused the leak. The drying of the interior must also be monitored. Residual moisture may still leave a mark even though the ingress of new water has been stopped.
If the problem returns, do not apply further layers without a diagnosis. It is possible that the source lies higher up or that the flashing requires rebuilding. A reliable repair should be describable: what was damaged, why it leaked and how proper functioning was restored. Choosing a stronger adhesive alone does not answer these questions.
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