Slate Roof Delamination

Over time these minerals expand causing layers to separate along cleavage planes.

Slate roof delamination.

Towards the end of its useful life these layers may begin to split apart in a process called delamination. You can also check for gaps in the mortar joints along the ridge line. Because slates are most likely to absorb moisture along their edges that s where delamination is often most obvious. This leads to a roof that is less sturdy and more prone to leaks and breakages.

Other causes of slate roof deterioration include. Worn slates at or near end of life in the upper roof above left. They can conceal easily repairable defects such as bad flashing or isolated broken slates. The most common defect i encounter on slate roofs is inappropriate repairs.

This problem is known as delamination. Such repairs are not only unsightly. 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. One example of this is chasing a leak with the black goop used by contractors unfamiliar with slate roofs.

Delamination is caused by the reaction of certain minerals to long term moisture cycles. Notice the surface delamination on some of these slates. Note the efflorescence on some slates and the delaminating slates. However the geological makeup and orientation of the slate can over time be responsible for delamination.

When it is used as a headstone zones of residual internal stress can result in the partial detachment of vertical planes. Slate is a naturally occurring resource that forms in strong but distinct layers. 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. Surface delamination on slates.

Some slates have been known to last over 200 years. Slate is a compact metamorphic rock geologically formed from fine grained sedimentary rocks of poor quality. You can spot a sloped slate roof tile more easily from the ground. If the tiles look to have a powdery surface this means the tile is deteriorating and you ll need to replace it.

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. At above right is a slate roof in poor condition on a poughkeepsie new york home.