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Problems with Slate Roofs - Nail Sickness

There are a surprising number of properties with slate roofs. One of the problems we often encounter is dislodged and missing slates caused by what is known as "nail sickness”. Nail sickness is a term used primarily with iron nails which were used to fix roofing slates to the roof battens beneath. As iron nails age, they corrode resulting in slate becoming dislodged and when it slips it can break and allow the ingress of rainwater.

This can be potentially dangerous to staff, customers, and patrons, as well as increasing the chances of leaks and property damage. One of the halfway hose fixes is called Turnerisation. This was a process first dreamed up by an American Henry Turner in 1897. It involves the laying of a mesh over the roof and then the application of a thick layer of bitumen and Hey Presto! The slates are stabilised and the roof fixed.

All very well for maybe even 10-15 years, sometimes even as early as 8-10 years, until sun and frost damage take its toll. Cracks appear in the bitumen and the state of the roof is back to as it was and many times harder to put right. Compared to a full roof overhaul, Turnerisation is seen as a cheap fix. More often used by Pubco roofing contractors with the sometimes seen result of no mesh underlay and a thin coat of bitumen. Once it is on there, there is no turning back and the ‘fix’ stays.

Another problem with Turnerisation is that a normal slate roof “breathes”, in that there is natural ventilation through the tiny gaps in the slate into the roof void. If there is a layer of bitumen there can be no ventilation and condensation can easily build up leading to a gentle increase in the decay of the roof timbers. Some buildings may not be affected at all and others the opposite.

It is worth noting that 'turnerising' or 'torching' is an alteration requiring listed building consent, which is unlikely to be granted, and that undertaking such work without consent would be a criminal offence punishable by a fine and, possibly, a prison term.

The first and correct way to fix the problem of ‘nail sickness’ is to strip the section of the roof and replace the corroded nails with modern copper nails. The second, perhaps the more temporary method is to keep the slates in place until the first option can be carried out. This temporary fix is carried out using a tingle or clip to keep the slate in place. These are usually formed from lead and nailed to the roofing battens, taken underneath the loose tiles and then neatly folded around the tail or lower edge of the slate. 

If you need your roof fixed linked with a Schedule of Dilapidations or need advice on a Listed property, get in touch with us and one of our experienced surveyors will create, on an initial free of charge basis, a bespoke plan of action for your property.

If you would like to know more about how we can assist further and anything else linked to your next move, please feel free to contact Morgan & Clarke on either 020 8103 3904 or by email on in order that we make an introduction to James Slater & Co.


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