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Are concrete roof tiles porous?

Are roof tiles porous?

If you have been told that your roofing tiles are porous, someone is either trying to sell you a new roof, or talk you into an expensive painting scheme. Roof tiles do not leak because they are porous. Read below to find out why your concrete tile roof may be leaking. 

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Concrete roofing tiles are manufactured from a mix of sand and cement. For aesthetic reasons only, the surface is then coated to provide different colour options. As with all concrete constructions, roof tiles become stronger as time passes. Due to age and weathering, the surface coating may well fade. However, this will not affect either the strength of the concrete tile, or its ability to shed water.

During construction of roofing tiles, water is a necessary part of the cement hydration. It also facilitates the mixing of the cement and fine aggregates. As the tile hardens the water is evaporated and the concrete becomes non pervious.   

Concrete is not susceptible to water related damaging affects, providing there is little or no moisture left after the drying period. In other words, providing the roofing tile was manufactured correctly prolonged exposure to moisture will have little or no effect.

 
 Double roman concrete roofing tiles, showing non porisity

The porosity of concrete roofing tiles has been measured. Roof tiles were subjected to prolonged water submersion under laboratory conditions. The maximum recorded absorption after prolonged submersion was ten per cent of the tile bodyweight. On the roof after prolonged heavy rain, absorption will increase the tiles weight by five per cent. This will not diminish the concrete tiles ability to shed water in any way. (Division of Building Research CSIRO Victoria)

Painting Concrete tile roofs

As mentioned previously, concrete tiles are coated immediately after construction for aesthetic reasons. After years of ultra violet light and weathering the concrete tile colour may fade. For aesthetic reasons only, you may wish to paint your roof. However painting the tiles will not stop roof leaks. If the roof is leaking, look for broken or dislodged concrete tiles, faulty flashing or degraded roofing mortar. Broken or blocked tile channels can also be a source of leaks. Written by    

 
Further reading: Porisity of concrete.