This one was a bit difficult for getting photos, as it’s on a sloped block and quite raised.
Nevertheless, here’s what we did and why:
This was a very straight forward job as it was all glazed, clay tiles. It was just time consuming and had a few safety considerations.
Glazed tiles are great for cleaning. As the tiles are manufactured, the clay that is used is actually a dry powder that’s compressed. Most people think of clay as being wet, but if clay containing moisture content is put into a kiln, it will violently explode and so dry clay is used. Once the tile has been fired however, a very small amount of Engobe is added to the surface. Engobe is a very runny, wet clay mix made only from the finest clay particles. Only a very thin layer is used, so there is no risk of violent cracking when extreme temperatures are applied.
Engobe is how glazed tiles get their shiny look, but it also has a functional effect. The very fine particles fill the porous surface of the tile, offering enhanced waterproofing and growth resisting properties. This is why glazed tiles are slightly faster and easier to clean.
The difference with glazed tiles is very minor and this particular roof was almost 60 years old. The amount of growth was substantial, meaning it required slow and thorough work to restore it’s look. The flip-side of this however, is that the before and after difference was great!
The safety considerations were due to the height of the roof. While it was only single storey, the sloped block meant that the front of the house was almost 3 metres higher off the ground than the back, which is not uncommon for Kalamunda. This simply meant that whichever areas didn’t have substantial fall protection from verandahs and pergolas etc. required a harness while working.
Other than the usual operating considerations, such as using certain cleaning techniques to avoid water ingress under the leading edge of tiles, we also had to be extremely careful around ridge caps. The roof had not had any re-bedding or re-pointing since it was built. Modern pointing compound is flexible and can withstand cracking from movement and thermal expansion, but this was almost 60 year old, brittle mortar. The owner hadn’t yet decided if they would be getting the roof re-pointed (we recommended that they do), so we were extra careful around ridge caps and only provided a very cursory pass over the cement pointing with the pressure washer, to avoid blasting it out.