Slate Repair

Natural slate roofs can last for generations, but individual slates crack, slip or break from impact, foot traffic or failed nails. Because each slate is held by nails hidden under the course above, repairs use special tools and methods that avoid disturbing the surrounding slates.

Removing the damaged slate

A slate ripper is a long flat bar with a hooked blade. It is slid under the broken slate, hooked onto a nail, and either pulled to extract the nail or struck with a hammer to cut the shank. The National Slate Association notes that pulling the nail out is preferred. After both nails are dealt with, the slate pieces and remaining nail shanks are removed so a full-length replacement can slide in.

Choosing a replacement

The replacement should match the existing slate in size, thickness, colour and weathering. Size is the most important, because it sets the headlap and offset. Reclaimed slates of similar age are often a better match than new ones.

Fixing methods

Nail and bib flashing. The new slate is slid into place and a hole is made through the joint between the two slates of the course above. It is fixed with a copper nail, and a small piece of sheet copper, the bib, is slid up under the course above so it covers the nail. US federal preservation guidance describes a bib about 3 by 8 in (75 by 200 mm), bent lengthwise and extending about 2 in under the next course.

Slate hook. A stainless or copper hook is nailed to the deck or batten in the joint below, and the replacement slate is slid down until its tail rests in the hook.

Copper tab. A narrow copper strip is nailed to the deck and folded up over the tail of the new slate. Federal guidance warns against this method in cold climates, where snow and ice can bend the tab open.

What to avoid

Materials that will not outlast the slate, such as galvanized nails, are discouraged because they rust and stain. Federal guidance suggests that if 20 percent or more of a roof needs repair, full replacement should be considered.