[log in to unmask] waxes nostalgically (about observed installations on high-end
1920's terrace and penthouse roofs):

<< Now yer talkin! The quarry tile (that is what it is called) is set on a
 mortar setting bed, usually 1.5 to 2" thickness. >>

So, Ken, am I getting the impression that you like such quarry tile
installations for penthouse roofs?  Or do you think the maintenance
requirements are unrealistically high?  And I didn't quite follow - do you
think the original 1920's installations meant to allow for "flow through"
(captured by a membrane underneath)?  Or is that a later development?  And
two inches of mortar in a setting bed - yikes, isn't that a lot?

And, most importantly, why don't they call it "furnace tile" instead?

Sign me,    Dated a Penthouse, but Married a Parlor Floor

PS Just heard from a client about a penthouse roof collapse in a 1920s
Manhattan building.  There was no steel left, but the tenant had built the
perimeter walls in about 2" deep.  That was enough to support the X mega-tons
of rust and concrete from squishing two people.