Fault diagnosis
Slipped Slates: Causes, Temporary Fixes and Proper Refixing
Slipped slate on a Birmingham roof. A slipped slate has lost its fixing, not its integrity, and the correct response depends entirely on whether the fixings around it are failing too. Filter the visible signs down to slipped slate or to the fault that mimics it, then book a survey. An exposed underlay is a temporary barrier with a short outdoor life; the urgency is real and is rarely stated.
A slipped slate has lost its nail fixing and moved down-slope out of course. What matters is whether it is one slate or a pattern.
An exposed underlay tolerates weeks rather than months before the leak begins. Cement dabbed under a slate cracks within a freeze cycle and traps water behind it. It is not a repair.
Why do slates slip?
Slates slip when their nails corrode and release, when a nail was overdriven and cracked the slate at fitting, or when wind lifts a unit whose headlap was already short. Corroded fixings account for most slips on period roofs.
Slipped slate is a slate that has lost its nail fixing and moved down-slope out of its course. Slipped slate exposes the underlay beneath to wind-driven rain and ultraviolet degradation; a tingle is a copper or lead strip nailed to the batten, folded over the slate's tail to retain it.
How urgent is a slipped slate?
A slipped slate needs attention within weeks rather than months. The underlay beneath is a secondary barrier designed to work briefly under a covering, and it degrades quickly once exposed to sunlight and driving rain.
Retains one slate only, remains visible, and does nothing for adjacent fixings. Cement dabbed under a slate cracks within a freeze cycle and traps water. The method is removing a band of slates to renail properly, used where several units in one area have gone.
How is a slipped slate refixed?
A slipped slate is refixed with a tingle: a copper or lead strip nailed to the batten and folded over the slate's tail. Where several units in one area have gone, a band is lifted and the slates are renailed properly.
- An exposed underlay tolerates weeks, not months, before the leak becomes structural.
- Slips across several slopes indicate systemic fixing failure rather than isolated damage.
- Storm loss is concentrated losses on one slope on one date indicate wind, not fixing failure.
Why should a slate never be mortared back?
Mortar under a slate cracks within a single freeze cycle because slate and cement move differently. The crack then holds water against the batten, so the patch accelerates the decay it was meant to stop.
A slate falling from a two-storey roof is a public safety matter.
- Slipped slate exposes underlay which degrades under UV and wind-driven rain.
- A tingle retains one slate without addressing adjacent fixings.
One slipped slate or a pattern?
One slip on one slope is isolated damage. Slips appearing across several slopes over months indicate that the fixings have reached the end of their life across the whole covering, which no amount of individual refixing resolves.
An exposed underlay is a temporary barrier with a short outdoor life; the urgency is real and is rarely stated.
- A mortar patch cracks under a freeze-thaw and traps water behind the slate.
- Scattered slips across slopes indicate a systemic fixing failure.
A pattern is a different problem.
When refixing stops being the answer
Cement under a slate cracks in one freeze cycle and holds water against the batten, accelerating the failure. Two slips on one slope is damage; two slips on three slopes is nail sickness. The distribution is the diagnosis.
Getting slipped slates refixed
Where several units in one area have gone, lifting a band and renailing costs less than repeated tingle visits.
Tingle, and 6 more
- tingle
- batten
- underlay
- course
- headlap
- strip lifting
- nail sickness
7 symptoms route to their own diagnosis: A damp patch on an upstairs ceiling, Water coming in with no visible damage outside, Slates or tiles slipped out of line, Water spilling over the gutter, Damp in the loft with no rain, A ridge line that dips in the middle and Moss across the slope.
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