Does Pressure Washing a Roof damage roof tiles?
Firstly I should state; this article is about roof cleaning in the UK, concrete or clay tiles and not ‘Shingles’ as used in the States.
There seems to be a lot of mistruths on various websites at present about the subject of pressure washing roofs.
Without a doubt, in the wrong hands, a pressure washer can damage roof tiles. An incorrect nozzle, extreme pressure or high flow rates, or a combination can remove the granular surface of a concrete tile.
However, an experienced professional roof cleaning company would know what lance/nozzle to use, set sensible water pressures and water flows, and, as a result, would not damage the roof tiles. The key point is to use ‘controlled pressure washing’, set pressures and flow rates to remove the weathering from the tile without causing any damage to the surface of the roof tile. Please click here to view photos on our Facebook page which shows close-up images of roof tiles, it can be clearly seen that there is no surface damage to the roof tiles.
Several major tile suppliers have recommended not to use a pressure washer. The reason for this is quite simple; by stating this they are protecting their products from inexperienced or the DIY enthusiast from possibly damaging their tiles. Similarly, the majority of paving manufacturers state not to pressure wash their paving slabs. What do you do when they become dirty and slippery, you can’t apply chemicals, as again manufacturers do not recommend them, and do you replace them? No, you clean them by pressure washing!
The NFRC (National Federation of Roofing Contractors) does not recognize the discipline of roof cleaning, they do not see moss as a problem. If the roof is heavily infected with moss they suggest a complete replacement. However, in the real world heavy deposits of moss on the roof is a problem. Moss falls from the roof tiles into the guttering system which can cause blockages and possibly dampness. The cynic in me wonders if they have adopted this stance to protect their members i.e. roofers
Incidentally, the main reason that we get approached by homeowners to clean their roofs, is not a concern of the condition of their roofs. It is simply that the moss is falling from the roof onto their new conservatory or patio, which is understandably a nuisance and a problem. Hence, it needs to be removed to protect their investments!
In contrast to the NFRC, all roof coating/roof tile coating suppliers require the roof tiles to be pressure washed before coating to validate their guarantee!