There are many companies on the internet advertising the fact that they can clean a roof without using a pressure washer. In some cases this is a valuable skill to have. We also offer this service – scrape off the moss with hand tools and then spray the whole roof with a cleaning product which kills the remains off the moss roots and algae. It does produce great long term results and in some cases it is the preferred method. Some concrete roof tiles have a granular coating which does wear off over time , but pressure washing can accelerate this process. However , If the tiles have already been exposed to the UK weather for a number of years then the coating will already have worn away. Pressure washing these tiles will not cause harm.
Both methods of Roof cleaning – pressure washing and manual scraping have there pros and cons. Each job should be assessed on its own merit , considering customer expectations and saftey. Whichever method is chosen , one thing is for sure – the tiles do need treating with a biocide cleaning product afterwards. This will inhibit the eventual regrowth and makes all the hard work of removing the moss and dirt worthwhile.
Another option is to ‘pre treat ‘ the roof before the cleaning process. This kills the biological growth infesting the roof tiles. Once moss , algae and in particular the very tough lichens are dead they are much easier to wash off. This means a much less aggressive approach can be taken with the pressure washer. The machines volume output and pressure can be carefully adjusted. Plus a good contractor uses correct selection of nozzles and jets .This method produces instant results.
If a manual scrape is chosen and the biocide treatment is applied after- results will show over the following months as the roof self cleans aided by the UK weather cycle. Some of the lichens are very stubborn and can take a year or more to weather off.
SO , yes – some roofs you can safely pressure wash.
