I was speaking to an architect earlier today and he had a question about the weight of slate tiles. He is designing a multi-floor building and was calculating the static loads that would be on the structural joists.
The weight of slate tiles will of course depend on the thickness. If the slate tiles are 3/8” thick, they will weigh around 5.5 lbs per sq ft. For 1/2” slate, the figure is around 7.3 lbs per sq ft and is approximately 11 lbs per sq ft for 3/4”.
When working out the upper limit that the slate floor will weigh, ensure that you always use the maximum thickness quoted, when given nominal dimensions of the tiles. And don’t forget the weight of the mortar! (The density of mortar is about the same as slate).
By the way, the information I gave the architect, other than “don’t forget the weight of the mortar!” was “0.104 lbs per cubic inch”. To calculate the full weight (in lbs) of the slate tiles and mortar, simply multiply the area of the floor by the thickness of the slate and mortar installation (all dimensions in inches). Then just multiply this by 0.104.