Many thinks for many comments. 

Generally I agree and hold the same concerns. These joints have long
been a source of water infiltration. The assembly is actually guastavino
tiles, with a bituminous coating on top of the tile layers and under the
grouted terra cotta roof tiles. Water that leaks in at failed joints
hits this coating and runs to the bottom and weeps out large openings at
the base intended for this purpose.

I don't know the original mix, as it's been replaced many times,
alternating between mortar and sealants. I think one purpose of the
additive may be to improve bonding to the glazed sides of the terra
cotta units, but this doesn't address movement across the entire dome
surface. Type N or S are just your standard options. Type S was used
back in the early 90s, but Type N is being proposed now, with the
additive.


QUINN EVANS | ARCHITECTS 
Ilene R. Tyler, FAIA, FAPT, LEED AP
v 734.663.5888

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