01
Read the test method and orientation
Slate is a natural layered material, so specimen preparation and loading direction matter. Use results from the applicable roofing-slate method and check sample dimensions and reporting units.
02
Do not confuse laboratory strength with abuse resistance
A compliant slate can still break under concentrated foot traffic, impact, poor deck support or an overdriven nail. Field workmanship controls stresses that a material report cannot prevent.
03
Compare representative production
A hand-selected strong sample does not establish consistency across a shipment. Sampling, traceability and delivery inspection give the reported values practical meaning.