The Usual Suspect: Bangor Slate
Owners of Bangor Slate roofs:
This is US quarried slate still in production but its also called builder grade slate. In 1900-1950 it was builder choice slate as it was the cheapest and still was called slate. The problem with this slate is that the life span is roughly 80 years only. The characteristic signs are grey with color streaks, flaking and golden hues. The slate have a tendency to fall off the roof. The main cause of this short life span is its very high moisture absorption. The slate, with time, will progressively absorb more moisture and become very soft and fragile. There is a fine line, as we tell to each potential customer of ours, when the repair of such a slate roof will still be productive and when the most sensible decision is to replace it. Unfortunately, the slate quality deteriorates so quickly that many times we feel it's wasting our client's money to try to replace each slate that falls or slides off. We believe taking care of the leak at the specific source if necessary, and, only when needed, replacing the affected section of roof. Any Bangor Slate in even slightly bad shape can't be ever properly fixed without an entire roof replacement. This is a very unique situation because all other slate species will not have this problem.
Bangor Slate is a notoriously poor quality slate quarried in Maine between 60 and 100 years ago. These slates will only last half as long as a proper slate.
Tin Flashing issues
For owners with badly maintained slate roofs or rusted out original tin flashing:
Broken or missing slate can only be properly fixed by correctly replacing the slate with a new, undamaged piece of slate(salvaged slate of same species is also OK).
Many homes built around 1920 were built during a copper shortage and copper flashing was used only on the most expensive roofs; the alternative was to use tin flashing. This weaker flashing rusts out eventually and will degrade even quicker on the areas that are hidden under the slate because it takes longer to dry and will be exposed to the water even longer.
We do offer complete and complex flashing replacement with all-new copper flashing on all valleys, chimneys, dormers, pipe boots, and anywhere else that is flashed.
Slates should always be nailed near the top end, where the hole will be covered by the next slate up. Face nailing is when a roofer deviates from this simple, crucial rule and nails through the front or "face" of a slate.
Face nailing only solves your roofers problem, not yours. When a roofer repairs a roof this way, he is not only doing a bad job of repairing your roof but he is damaging it further! A nail through the exposed face of a slate, as with anything you put a hole in, is no longer waterproof; however, he is not only ruining one slate, but also the one below it, making a hole straight through your roof.
Another issue with face nailing is when new snowguards are installed. As demonstrated below, the snowguard installer might just put a face nail through to get the job don quickly, despite it being an incorrect and damaging "repair".
If you think your home may have issues with face nails, give us a call and we'll happily come out to inspect any potential damage and give you an estimate!