Skip links

Astonishingly Crude

That’s a close-up, obviously, of a street facade of a New-Law Tenement. The arch in the lower right is a window head, and is actually four courses of brick, with the top course being headers that cantilever out to create a hood over the window. It’s a nice detail, creating architectural effect without changing material. And the iron-spot brick is, depending on your taste, either quite beautiful or looks like it’s being attacked by a robot fungus. 

Two issues jump out from this photo. The first is that the mortar joints are badly eroded and therefore badly need repointing. That’s not really a surprise, although the extent of the issue is. The second is how sloppy the original construction is where the field of the wall meets the arch.

It’s bad enough that the arch bricks – the voussoirs – are ordinary bricks with rectangular-prism shapes. That means the mortar joints are wedge-shaped, which is not particularly good for weathering or load performance and is, at this close range, unsightly. More unsightly, where the bricks in the field of the wall abut the arch, they were saw cut at, apparently, a guess as to the angle. The brick on the lower left shows three separate kerfs where someone started sawing that brick. It is embarrassingly sloppy work, except that it was performed about 110 years ago, so I suspect the mason is beyond embarrassment.

The punchline is that it doesn’t matter. As far as appearance goes, this joint cannot be seen from the street and can barely be seen from neighboring buildings. As far as load transfer goes, the compressive stress in the front (non-joint-bearing) wall of this low-rise building is quite low and the forces can adjust around a defect. And as far as weathering goes…solid brick walls are a bit of magic. Bricks are porous, mortar is porous, and the geometry is regularish but full of small defects, but the walls taken in their entirety are quite waterproof. The (more or less) solid nature of the wall eliminates internal air-pressure differentials that can accelerate water entry, so water can only get in through by capillary action with pores and whatever gaps (like the ones in the photo) exist. Given enough time, every brick wall would leak, but rain eventually ends, and the water stops getting pushed in and starts getting pulled out. There weer no leaks associated with the cut-brick gaps here.