Avoid Slate Roof Problems

How to Avoid Problems with Slate Roofs

Jim O Donoghue, Director, Killoran Slate & Tile.

Fibre-cement roofing slates look best when new!

The colour of most painted (Man-made ) roofing products will fade from day one as a result of ultra violet degradation. The paint layer will eventually wear off.

I have been selling fibre cement slates for 30 years and it is my personal experience. The loss of colour will be accelerated in coastal areas, in my opinion, lasting less than 10 years despite what some manufacturers put down on paper.

Problems with Poor Quality Natural Roof Slates

I have seen poor quality natural roof slates which have faded from a blue/black colour to grey/white within 3 years. Those slates are sub-standard and certainly NOT in conformity with the T1 – S1 – A1 categories laid down in the European Standard for natural slate BSEN- 12326-2:2004. 

I have also seen natural slate roofs which had to be reslated within 5 years because the slates were either cracking, disintegrating or badly fixed. Leaching of unstable “ pyrites “ can result in holes in the slate leading to leaks.

Some slate sales men have been promoting  HOOK FIXING in addition to nailing slates in recent years. Hooking natural slates is being put forward as if it is performing the same function as the copper (storm) crampion at the tail of Fibre-cement slates. This is “concealment” to put it mildly. Cross grained slates and “mud” slates are far more susceptible to cracking below the nail holes and they fall off the roof. Then you see the slate missing so you replace the slate without delay to prevent water getting into the roof. If a hooks are also used, then the broken slate is retained in position, water entering the crack over a prolonged period of time will eventually rot the breather membrane and after perhaps many years you see the leak after a lot of damage has been done.

Hook fixing THIN natural slates in areas of SEVERE EXPOSURE is bad practice. A Heavy Grade slate can be 50% thicker than a Premier grade slate from the same quarry, therefore the Heavy Grade slate is much stronger and more appropriate for use on severe exposure sites. Visit to Killoran Slate & Tile Depot  (bring your Slating Contractor also) and you will see the slates in the crates BEFORE we despatch to your site.

Crates of 50×25 slates from the same quarry will have about 700 Premier Grade or 600 Standard Grade or 450 Heavy Grade in each crate.

HOOKING is not the solution for severe exposure, the proper solution is to specify the appropriate best quality natural slate and have it fixed with 2 copper slate nails (40mm x 3.35mm dia) to a TREATED batten size 50mm x 38MM. We recommend that slate roofs should be counter battened to further reduce the risk of interstitial condensation. The thicker slating batten allows you to use a longer copper slate nail for increased grip and reduces the risk of protruding nail points damaging the breather membrane.

Counter battening allows unobstructed air-flow from EAVES to RIDGE and prevent slate chippings being trapped between the slating batten and the Breather Membrane.

Roofing Contractors must be Experienced with Natural Slates

To get a good slate roof you need best Quality natural slates AND you also need a professional Slating Contractor who has long experience with natural slates.

Natural roof slates are not flexible. Slates damaged during the slating process must be replaced. Lack of proper sorting and grading results in poor appearance and may lead to slates being blown off in severe storms. Nailing too tight leads to slate failure on the roof.

Experienced SLATERS will always carry out a final check for any damaged slates on the roof BEFORE taking down scaffolding and roof ladders. Broken or damaged slates can easily be replaced immediately with purpose made copper strips which we have in stock. Many cracked slates occur as a result of roof traffic – the message is “ NEVER WALK ON A SLATE ROOF “.

Dirt will accumulate on a slate roof. The sheltered side of a roof will accumulate more dirt especially if near high trees or in a dusty environment. Dirt will encourage the growth of moss and lichens. Natural slate roofs can be power washed to remove dirt.

High pitched roofs (over 45 degrees) will remain much cleaner than low pitch (say 25 degrees). Very high pitches are less likely to suffer foot traffic from being walked upon. Careful use of power washers will remove dirt from natural slate roofs.

All elements of buildings require routine care and maintenance. Natural slate roofs are no exception.

  • Keep gutters and valleys clear of debris.
  • Check lead work around chimneys, gables, flashings  and abutments etc.
  • Make sure that ridge tiles are firmly bedded and that the joints are keeping water out.
  • Make sure that all lead or copper work is free from cracks or holes. Middle valleys are particularly prone to damage from loose slates sliding down into the valley. By the time leaks display internally serious water damage will have occurred.
  • Replace any cracked or broken slates. Use a ripping iron to remove damaged slate and replace with sound slate and using either a slate hook or the copper slate strip fix to retain slate in position.

Choose the Best Option – Best Quality Spanish Natural Slates fixed by a Professional Slater.

New natural roof slates from Killoran Slate & Tile are colour durable and require little maintenance over a life span of 100+ years. We have been supplying best quality natural slate and tile roofs for 30 years. We can give reference sites locally if anybody wants to see how the roof slates have aged with time. Best quality natural slates, properly fixed by an experienced Slater, in accordance with the Codes of Practice for Slating & Tiling, should remain in position for many decades in normal weather conditions. Dirt will not damage or shorten the life expectancy of best quality natural slates.

Appoint a professional Slating contractor who will sort and grade the slates properly on site – using the heavy slates in courses near the EAVES – medium thickness in the centre and light slates nearest the ridge. The Slater should also mix slates from at least 3 different crates when stacking the roof to achieve an even dispersal of shades throughout the roof. Use wide slates at verges, around roof windows and abutments etc.

The Slater is best positioned to prevent any damaged slate going on the roof as he can examine and tap each slate while fixing . Remember it is the final covering ( the slate ) which most influences the long life of the roof.

All other materials such as membrane, battens, and copper nails are usually the same irrespective of the life span of the slate chosen. The fixing labour for natural slates is the same . We strongly recommend upgrading to the best quality natural slate to increase the longevity of the roof.

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