Roof tile coatings are designed to improve the appearance of the roof, but few roof coating companies will tell you how it may invalidate the guarantee offered by the tile manufacturer.
For example, Santoft provide a 60 year guarantee on their concrete tiles and Redland offer a 15 year guarantee.
Here is a statement from Redland Roofing:
Finally, it should be borne in mind that most, if not all, tile manufacturers, Redland included, offer product guarantees regarding the durability of their tiles. The use of such surface treatments will invalidate these guarantees so unless similar guarantees are being offered from the supplier of the treatment most tile manufacturers would advise caution.
RoofCoatingScam believes that a homeowner may experience difficulty making a successful guarantee claim to a tile manufacturer once the roof has been pressure washed and coated.
The pressure washing of the tiles and the application of a roof coating may also invalidate any NHBC (National House Building Council) guarantee which is often provided to owners of newly constructed houses. They currently provide a guarantee of up to 10 years for roof coverings.
Advice from Tile Manufacturers
The following statements were issued by roof tile manufacturers:
We do not recommend pressure washing roof tiles. (Redland roofing)The use of high powered jet washes is not recommended as it can damage the surface of the slate or tile, thus reducing its expected life considerably. (Marley Eternit)