All Points Bulletin: Be on the Lookout for Butchers Masquerading as Slate Roofers!
It is an unfortunate fact that the cause of many leaking slate roofs is not natural wear, metal flashing failures, or even cracked slates. It is, quite simply, bad work. Many unqualified people claim to have the ability to repair slate roofs. According to the Slate Roofing Contractors' Association, fully
half of the work done annually by a typical slate roofing contractor involves the removal and replacement of faulty repair work. Home owners with slate roofs often pay exorbitant sums only to have their roofs trashed by these fly-by-nighters ... they then have to pay even more of their hard-earned money to have them fixed and repaired correctly! The abuses committed against slate roofs include face-nailing, tar-smearing, repairs with non-matching slates, inappropriate coatings, or incorrect flashings.
First and foremost, a warning straight from the heart: One should NEVER tar or coat the surface of a slate roof. Such actions are aesthetically displeasing, often irreversible, and ultimately ineffective. Sadly, roofing contractors are notorious for advising homeowners to replace a perfectly good roof. Home owners will often listen to such advice when a lack of competent slate roofers makes it the only advice available. These issues, combined, have been the downfall of countless slate roofs, lost forever to ignorance, neglect, and despair. As you seek estimates and advice from other roofers, use the information in this blog to test their knowledge and screen their methods. Watch their eyes widen as they realize that YOU know more about slate roofing than they do!
It is not uncommon for a century-old slate roof to have 50 or more slates simply fail from a variety of causes. Slate contains natural faults or hairline cracks and may eventually break. A 20 square roof (2,000 square feet), with a typical 10"x 20" slate, will have about 3,400 slates. If 50 of them fail after a hundred years, then the failure rate of the roof is 1.5 percent over 100 years- or a 98.5 percent success rate over a century. That's an A+! However, just one missing slate is all a leak needs to get started. For a professional slate roofer, the solution is not rocket science. Replacement slates must never be fastened in place with visible straps or exposed nails (known as "face-nails"). If a roofer describes face-nailing to you as his preferred method of repair, you're done-you've just met one of the butchers who roams about, masquerading as a slate roofer. NEVER let him anywhere near your roof!
There are two acceptable techniques for fastening replacement slates: the "nail and bib" method or the "slate hook". The nail and bib method is the most widely used. The broken slate is removed with a slate ripper and the replacement slate is anchored with a nail in the slot between the two, overlying slates. A small square of flashing is slid under the two, overlying slates on the next course, above, and over the new nail head. The bib is bent a little so friction keeps it in place. Bibs can be aluminum, copper, or other non-corrodible metal, but shiny and reflective metals that are visible from the ground should never be used.
Oh and, by the way, all true slate roofers call themselves slaters. If a prospective roofing contractor doesn't smile and embrace the term in your initial contact when you ask, "Are you a slater?" watch out! Just might be a butcher in disguise... 