Historic bricks are too soft for modern mortar

Recently, while visiting a client’s house we looked at these side facade. The houses is an end lot so there is a yard beside the house and that side wall is a largely contiguous uninterrupted brick wall. Along the bottom of the wall there are a few spots where bricks have spalled. Upon closer examination, we could see that the fracture line in the brick was directly coincident with where the brick had been pointed in reason years by some other contractor before the client of mine bought the house. The previous contractor used a modern mortar instead of a softer motor.

The bricks are historic and they are a common brick so they are particularly soft and have a low PSI strength. In this case the new modern mortar is much harder then the bricks and it in the case of the picture below you can see that the brick has spalled directly in line with where the new mortar entered into the mortar joint.

Buildings move. Sometimes that movement is very small and just the tiniest about. Imagine over a 30′ tall wall the building moves just a millimeter in the time that it takes the building the heat up an additional 50゚. It doesn’t have to be that much but the wall is so hard and heavy overall that when the soft bricks move with new hard mortar between them it can cause the face of the brick to crack and in this case the brick face spalled or cracked directly off. It’s a perfect example because the remainder of that face of the brick stayed completely in tact.


One example of an old worn brick chimney

The chimney the pictures below is probably well over a hundred years old and looks as if it’s never been repaired or pointed.

The mortar joints are deteriorated so bad that the bricks themselves are almost loose.

Also, you can see this chimney has no spark arrestor or cap. So essentially rain water or precipitation will just go straight down inside of the inside of the house and there’s nothing to keep rodents out such as a rodent guard, and leaving the top flue is missing.

The remarkable part is that if you know Capitol Hill and DC houses well then you know that this is actually not uncommon. This particular chimney is overdue for some restoration though at this point.

Wood grain left in a concrete wall

The formboards used to build the wall in the photo below left a natural wood grain, just like the original historic formboards did about 50 to 100 years ago.

Concrete is poured into a form in a wet consistency similar to a slushy wet mud. The concrete hardens quickly and within a few days to about a month the country forms can be removed from the new concrete construction.

In modern times we have several materials we use to build our form and walls, including: plywood, melamine veneers, PVC, and more. But in the old days, in historic construction wood planks were used.

This building wall, shown above was built to resemble the Historic style and methods of construction, but in reality there is a sauna to that indicates the Historic effect is actually artificial and not actually historic:

1. If you look very closely you can see there are round spots in the concrete of the wall face that are approximately the size of a quarter or half dollar, about 1.25 inches in diameter. These spots look like a snap ties used in modern forms, not used in historic forms. The snap ties have a plastic collar that prevents the form sides from being squished together.

2. The building above the base wall shown is a high rise building. It’s very unlikely that historic foundation would have been built to the standards required for a modern high rise building.