Slate Roof Delamination

You can spot a sloped slate roof tile more easily from the ground.

Slate roof delamination.

Notice the surface delamination on some of these slates. This problem is known as delamination. Delamination occurs when impurities contained within the slate primarily calcite and iron sulfides such as pyrite and marcasite react in association with hot cold and wet dry cycling to form calcium sulfate gypsum molecules that take up slightly more volume than the original minerals. Delamination is caused by the reaction of certain minerals to long term moisture cycles.

This leads to a roof that is less sturdy and more prone to leaks and breakages. Note the efflorescence on some slates and the delaminating slates. They can conceal easily repairable defects such as bad flashing or isolated broken slates. You can also check for gaps in the mortar joints along the ridge line.

Surface delamination on slates. When it is used as a headstone zones of residual internal stress can result in the partial detachment of vertical planes. Other causes of slate roof deterioration include. Installed properly slate roofs require relatively little maintenance and will last 60 to 125 years or longer depending on the type of slate employed roof configuration and the geographical location of the property.

Over time these minerals expand causing layers to separate along cleavage planes. Worn slates at or near end of life in the upper roof above left. Slate is a compact metamorphic rock geologically formed from fine grained sedimentary rocks of poor quality. Towards the end of its useful life these layers may begin to split apart in a process called delamination.

We see numerous broken slates slates with holes delamiated thin slates loose slates sliding down a few temporary repair slates. Slate is a naturally occurring resource that forms in strong but distinct layers. Also ask how many of the roof slates are delaminating at all note the neighboring slates on this roof are sound. The delamination of poor quality slates where they split into layers mechanical damage like wind lift bad slating practice for example the use of thin nails that eventually cut through slates.

If the tiles look to have a powdery surface this means the tile is deteriorating and you ll need to replace it. The most common defect i encounter on slate roofs is inappropriate repairs. At above right is a slate roof in poor condition on a poughkeepsie new york home. Some slates have been known to last over 200 years.

Because slates are most likely to absorb moisture along their edges that s where delamination is often most obvious. Delaminating roofing slate if the delamination is only in the upper surface layer of the slate the material may have substantial remaining life.