Slate Roof Delamination

Surface delamination on slates.

Slate roof delamination. Slate is a compact metamorphic rock geologically formed from fine grained sedimentary rocks of poor quality. 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. Also ask how many of the roof slates are delaminating at all note the neighboring slates on this roof are sound. You can also check for gaps in the mortar joints along the ridge line.

Other causes of slate roof deterioration include. Such repairs are not only unsightly. Delamination is caused by the reaction of certain minerals to long term moisture cycles. You can spot a sloped slate roof tile more easily from the ground.

When it is used as a headstone zones of residual internal stress can result in the partial detachment of vertical planes. Worn slates at or near end of life in the upper roof above left. One example of this is chasing a leak with the black goop used by contractors unfamiliar with slate roofs. This problem is known as delamination.

Because slates are most likely to absorb moisture along their edges that s where delamination is often most obvious. At above right is a slate roof in poor condition on a poughkeepsie new york home. Note the efflorescence on some slates and the delaminating slates. 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.

The most common defect i encounter on slate roofs is inappropriate repairs. Notice the surface delamination on some of these slates. Over time these minerals expand causing layers to separate along cleavage planes. This leads to a roof that is less sturdy and more prone to leaks and breakages.

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. Delaminating roofing slate if the delamination is only in the upper surface layer of the slate the material may have substantial remaining life. They can conceal easily repairable defects such as bad flashing or isolated broken slates. Towards the end of its useful life these layers may begin to split apart in a process called delamination.

If the tiles look to have a powdery surface this means the tile is deteriorating and you ll need to replace it. We see numerous broken slates slates with holes delamiated thin slates loose slates sliding down a few temporary repair slates.