01
Do not diagnose from age alone
Inspect the removed fastener and slate hole where possible. Copper nails, steel nails and hooks fail differently. A broken slate head can mimic a corroded fastener.
02
Look for a pattern
Scattered isolated slips suggest a different problem from repeated rows or whole elevations. Orientation, moisture exposure, deck type and past replacement work can help identify the cause.
03
Repair the cause and the opening
Replace or secure the slate with an accepted method and examine surrounding pieces. If systemic fastening or deck problems exist, a larger repair plan may be necessary.