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Quite often when I’m working on a slate roof – be it a repair or a new installation, neighbours or passers by, often have a question or two about their own slate roof .
Sometimes they just have a simple question that can be easily and quickly explained. Sometimes they’re looking for a more in depth answer to a more complex issue they’re having or going to need an answer to in the future.
What qualifies me to answer these questions you may be asking.
Well …. I completed a formal apprenticeship which finished in 1981 and culminated in being awarded outstanding apprentice of the year in roof slating and tiling. But I feel more importantly than this, I spent about 8 years during the early to mid 80’s working with a true master slate roofer who had spent his first 40 working years roof slating in Wales and Scotland. After immigrating to Australia in his latter years, he became the teacher for slate roofing at Collingwood Technical Trade school which is where I met and became great friends with him. The knowledge this guy had regarding slate roofing was truly astounding. Every weekend or holiday period we’d be up on a slate roof somewhere around Melbourne. I’d like to think I learned a little something during the years we spent as friends working on all those slate roof repairs, restorations and re-roofs.
Here’s the list of probably the most asked questions and their answers
What exactly is roofing slate ?
In short…roofing slate is a thin sheet of argillaceous sedimentary rock that has been split along its natural lines of cleavage. The rock has been formed over many thousands of years of being subjected to great geological pressure. It is a completely naturally made product.
Slate roof tiles
What is a good roofing slate for Melbourne’s conditions ?
Good roofing slate suitable for Melbourne would be classed as a good slate almost anywhere in the world. Good
quality slate could be defined as being hard, finely grained, compact and almost completely impervious to all substances. Good quality roof slate is not affected by damp, heat or frosts, unlike some concrete and terracotta roof tiles. Due to these outstanding qualities it really deserves its place as the premier roofing material in use in Melbourne.
Now what’s a poor quality slate for roofing you may be wondering. A poor quality slate, always presents itself in Melbourne by being relatively cheap compared to the good ones. The physical characteristics can be all or just one of the following:
- Calcium Carbonate in the slate – If present in the slate causes the roof to fade when exposed to the sun. This fading continues on to different degrees giving it an unsightly chequer board appearance. If there’s a lot of the Calcium Carbonate in a lot of the slates, the roof can almost turn to a white colour. As well as the colour change these slates are now usually very soft and water absorbent.
- Pyrites in the slate – Whether visible or not visible to the eye, pyrites are small particles of an iron ore type substance. When exposed to the weather over a short period of time, the particles begin to rust and cause streaks of a rusty red colour stain down the roof. If there’s large particles of pyrites present in the slate, they can also completely rust out leaving holes through the slate.
- Soft or not dense enough slate – Some slate available for roofing is simply not hard or dense enough. This type of slate allows too much moisture to seep below the surface. What then happens is that this moisture below the surface can freeze and expand causing the slate to begin to ‘delaminate’, or slowly fall apart over time if you like.
- Thickness variations and lumps in the slate – All roofing slate comes in slightly varying thicknesses to some degree. It’s the job of the roof slater to sort through these slates and grade them accordingly. These grades can then be laid together on the roof, however the slater feels is the best way to get a nice tight flat sitting roof. However ….. slates of a poorer cheaper quality will often have a large variation in thickness as well as thicker and lumpier spots on the individual slates. What does this mean ? It means try as hard as you can to sort and grade them, they still won’t sit flat, or tight down on the roof. They never look as good as the good quality slates.This slate has small amounts of pyrites and Calcium Carbonate
Are there different colours of roof slate available today?
It is true that after being exposed to pollution for probably over 100 years, most of Melbourne’s Victorian and Edwardian era homes slate roofs have changed colour to a browny-grey shade. These original slates would have been many different colours when first installed, not the one colour that most people assume slate roofs to be today. This pollution staining can be removed with a bit of hard scrubbing with a diluted caustic solution and apart from removing the staining has no other effect on the slate.
If you want proof of original different colour slate roofs, venture out to a country town like Kyneton, or Kilmore, and look at the slate roofs. You’ll see virtually pollution free different colours of slate roofs.
These days there are a few different colours of slate available… not the large selection that the Victorian era home builders had available to them but still a fair range. These are the colours available at present that I consider to be a good quality slate. Remember slate colour is completely natural… not man made.
- Cupa – Slate from the North West region of Spain. Deep blue in colour.
- Del Carmen Ultra – Spanish slate. A very deep blue, charcoal, almost black colour
- Bugail – Welsh slate. A grey- blue colour. Slightly lighter than Spanish
- Penryhn – Welsh slate. A light purple plum type of colorOriginal slates showing some different colours… the grey ones are soft.
How long do slate roofs last ?
A good quality slate roof in Melbourne can last well over 100 years; even a lot longer. There are still original slate roofs around Melbourne that are around the 150 year mark. Some of these are definitely in varying stages of needing a bit of restoration but overall they’re still performing. Others the same age have been maintained and had restorations over the years and are in excellent shape.
On the other side of the coin you’ve got the real cheap poor quality slate roofs. We’ve come across some slate roofs around the 15 – 20 year old mark that can’t be saved and simply need to be re-roofed. Probably the worst I’ve seen and replaced was about 11 years old; and it was causing problems for a few years before being replaced.
We believe that a good quality slate roof in Melbourne should easily last in excess of 100 years.
Should I have my slate roof inspected even if it’s not leaking ?
That really depends on how old the roof is. If its less than 10 years old and was installed properly and with good quality slate, I’d probably say no, not really at this age. Unless there’s something that’s bothering you, or you’re unsure about, there’s usually not much that goes wrong.
On the other hand, if your roof is a Victorian or Edwardian period home and has never had any restoration type of work done to it , then yes, its a good idea. I would say annual or at least biannual would be a good starting point. An honest and real slate roof specialist should be able to suggest a time schedule for you to have check-ups after an initial inspection.
Just as an example here. We have customers whose roofs we check twice per year. Their roofs are old and in ordinary to poor condition. These roofs have done a fine job for over 100 years but they now need a full restoration, or if the slate is no longer any good, a complete re-roof. Mostly these people are just keeping their roofs water tight until they decide what they’re doing. Sometimes they’re not sure if they’re staying in the house for long, or they’re going to extend soon, so want to wait to have the roofing done all at the same time… which is a good idea. Sometimes its quite simply the cost of restoring or replacing.
We’ve also had customers whose roofs were restored 20-30 years ago. Each individual inspection can reveal different things that may need to be watched over the years at varying time intervals.
Slate roof inspection time frames can vary greatly. If you haven’t had one and don’t really know the history of the roof on your home, it may be a good idea to get one and follow the recommendations of the roofer. Just be sure to use a properly qualified slate specialist.
What we’ve found over the years is that its easy for our customers to just forget about their roof until it’s too late. By the time a leak is noticed, its already done quite a bit of damage which can add up to being expensive to repair.
With smaller leaks, the water can often be absorbed by insulation and even plaster to a certain extent. While the damage isn’t huge, they can still cause mould and damp smells in the rooms. We’ve also seen small leaks cause power to trip off at safety switches.
An inspection found this gutter rust problem before it began leaking
Can or should you walk on slate roofs ?
Unlike most tile roofs, the pitch, or steepness if you like, is generally a lot greater on most slate roofs. The old original slate roofs on the majority of Melbourne’s Victorian and Edwardian period homes have a pitch of around 28 – 35 degrees. This itself makes walking on these roofs quite difficult. Add the moss that’s nearly always present on the slates and it’s not only difficult but dangerous as well.
Where it is possible to stand and walk on the roof, you also need to take into consideration the condition and quality of the slates themselves. If the slate is soft, your foot may go straight through leaving a gaping hole. If they’re brittle it’s easy to snap and crack them… both scenarios requiring repairs.
So to answer the question… you can, but it may be difficult and dangerous and probably best left to an experienced slate roofer to avoid injury or damage.
Does the lichen and moss on my slate roof harm it in anyway ?
In Melbourne you’ll find that most of the mosses grow on the South facing sides of your roof. The other faces do get moss also but not to the extent as the South, with very little on the North side. Some people find the look of the moss unsightly but I’ve never seen it do any damage to the slates themselves or affect the functioning of the roof.
The one thing that sometimes happens on very low pitched roofs which have a lot of moss, is that it blocks the water flow forcing it sideways and into the roof.
This only happens where there is a large volume of rain water coming down from a steeper and larger area above the flatter one. Usually this area is a verandah or skillion that’s facing the North.
Typical moss coverage on a shaded South side old slate roof
Can moss and lichen be removed from the roof
There are a few different ways to remove moss from slate tiles but none will be long term. A few years later and the moss will be back just like before.
Methods used are pressure cleaning, chemical spray and hand scraping. I don’t see it done very often and I’m certain, if not careful,there’d also be a bit of damage to the roof in the process.
If it really is causing a leak, as in the question above, the best method would be hand scraping. What we’ve done in the past to stop these low pitch slate roof leaks is this:
- The area of slate that’s leaking is stripped from the roof
- The slate battens are removed also
- Heavy duty sarking is applied to the top of the rafters and carefully turned up at any abutments
- New oregon slate battens are then installed on top of the sarking and rafters
- All the removed slates are cleaned of moss by hand with a paint scraper
- The slates are the relaid on the roof
This method always stops the leaking, but as you read above the moss eventually grows back. Now however, in the heavy downpours when the moss causes the low pitch area to leak a little, the water is picked up by the sarking and carried to the spout.
If you’ve got any specific questions regarding your own slate roof and need help or just advice… Call me John 0403022137
It doesn’t matter where you live, our slate roof services in Melbourne are carried out in all suburbs.
Here’s a recent project we completed. The job entailed alterations and installation of slate roofing in Kew
Abardeen Roof Slating & Tiling 66 Eglinton St Moonee Ponds VIC 3039