Who Invented Hollow Bricks?

I have no idea where this fits but ... here's my rant:

My 1975 house has a massive two-storey brick chimney -thing extending from the basement through the roof. It was designed for two poorly-drawing wood fireplaces meant to impress rather than add heat.

In the days before cheaping out, this would have been a colossal thermal mass waiting for the right person to make use of it.  Unfortunately, except for the directly heat elements, it is constructed of thermally useless hollow brick. It's a waste of space, nothing more. It would cost a fortune to rip it out and replace. For this place, the numbers don't work, so it won't happen.

The designer has not left a forwarding address, which is probably just as well. Some days I am inclined to look him up.

End of rant. Thanks for listening. Argh!

Douglas,   We could probably re-create a journey of your chimney builder down through central North Dakota and ending up at our place south of Fargo......where he built the west wall of our house foundation.  The south, east, and north walls are all made of standard 8" thick cinderblock.  But the west wall.....the one that gets all of the hydrostatic pressure....was constructed, for some bizarre reason, with 6" thick blocks!  Even the iron girders installed after the flooding of 1997 to support the 4 walls are of little help and the wall is buckling between the supports.  Someone needs to create a web-page entitled "Home construction disasters.....and the people who live in them"... :-/

Douglas said, " massive two-storey brick chimney

Maybe this is the mass as in a rocket mass heater waiting to happen.

Ouch! You have the massive size, without the mass.

Sadly, way too many houses are built for appearance and minimal cost, with no thought for functionality.  We live in one, as well. :(

If you can open up the top of the chimney enough to gain access to the hollow cavities, you may be able to fill them with sand, then recap.

I have a similar mid 70s ranch with a wood burning FP in the basement and LR.   Fortunately, I do have the mass from solid brick. Unfortunately both are built around prefab  metal Heatalators (not stove type Inserts) that are too small to be truly effective. The FP openings need to be a foot larger in all dimensions.   Of course, the space is there. My gawd, the brick wall is 12 feet wide by 16 ft tall and 3 ft deep. The problem is, it was designed for pretty and not function. Of course, it could have been designed for both.

I asked Mr. Google:

Who invented hollow bricks?

the guardian said, "What is the hollow in a brick called?
'Frogging' – the familiar (usually pyramidal) indentation in bricks – originates from the ancient Egyptian custom of creating hollows in their Nile-clay bricks, in which they interred live animals (usually infant) as building work progressed.

seattle times said, " 1. Holes save raw materials for the manufacturer. · 2. The holes make the bricks weigh less. · 3. Holes allow a consistent heat distribution

Do you have a fireplace that goes with that chimney?

This sounds like the perfect place to set up a Liberator (rmh.)

My understanding is the holes allow rebar to be placed.

My grandfather was a bricklayer for most of the 20th Century stopping only for a few years during WW2.  He really liked talking about it when I was a kid.  This is the information I got from his ramblings - note, I don't have personal experience with this so I don't know what parts are just his opinion and what parts other bricklayers would agree with.

When he started, bricks were made locally as transporting something that heavy and bulky didn't make sense.  

The frog - one company local to him had the frog in the shape of a frog - had a depression on one side of the brick so the mortar had something to grab hold of and the wall will find it more difficult to fall down.  

Solid bricks are hell for radiating cold into the house and were extremely expensive to heat.  They grab the chill and the damp and they put it right into the people trying to live in the house.  So most houses he helped build had two walls with an air gap between them.  This made a huge difference and according to my grandmother took less than 1/3rd the amount of coal to heat the same size house.

The hollow bricks have little pockets of air, so they were a huge game changer in reducing the worst part of living with bricks - the cold.  Like how fluffy insulation has a higher R-factor than the same insulation compressed flat.  Air is a huge helper in insulating.  

The hollow bricks were also lighter and with improvements in transportation, they could now ship bricks all over the world and places without the right sort of clay could have brick houses.


As time progressed, he began to specialize in fireplaces and chimneys.  These require a different kind of thinking to walls.  They had to be built to allow some expansion and contraction from temperature change.  He would often use different kinds of bricks in the same chimney/fire palace depending on the needs and locations.  Where is going to get the most heat, where isn't, what's going to be visible... all that stuff.  

Thermal mass wasn't a big consideration in the parts of the world where he trained, insulation was the bigger concern.  The goal was to prevent the heat or cold from transferring into the living space and since fuel was rationed for the first half of his life, the idea of having a fire hot enough or long enough to heat up a mass like a chimney was impossible for him to imagine.  You had the fire for cooking and heating up cleaning water, and the rest of the time you wore layers in the house to keep warm.  If you wanted to write a letter in the winter, you put the ink bottle inside your vest (like a tank top worn next to the skin) until enough of the ice crystals melted.  In those conditions, having hollow bricks wasn't such a bad idea.


But you live in a different time and place.   Your needs and resources are different.

for reference, this is what I mean when I say frog.  It's the hollow impression on a 'solid' or hand moulded brick.  


from here

and here are even more details in case you want to go down that rabbit hole

I can think of several types of brick that might be described as "hollow".

These are common bricks in the UK. They have a "frog" which, as R Ranson explained, is to allow the mortar to key into something.

r ranson wrote:The frog - one company local to him had the frog in the shape of a frog - was a hollo on one side of the brick so the mortar had something to grab hold of and the wall will find it more difficult to fall down.

Old, factory bricks often have interesting-shaped frogs and the name of the makers stamped into them. I have quite a large collection that I have been salvaging with a mind to build a big pizza oven.



Then there are these bricks, with several holes that go all of the way through them. This would serve as a key, of sorts, for mortar but I suspect there is a different use for these (such as rebar, suggested by Thomas). I think this type of brick would have reasonable insulation properties too.

thomas rubino wrote:My understanding is the holes allow rebar to be placed.

The final kind of brick that I am familiar with is this, truly hollow variety. I've seen these used in Portugal and in India. They are super lightweight and feel very strange to pick up and move around. They offer quite a lot of insulation but very little in the way of thermal mass. They are also much weaker than solid clay bricks, as you might expect.

My grandfather would refer to the bricks with a hole all the way through as 'hollow'.  The mortar does go into the holes a bit but there are still air pockets in the wall.  The air pockets are the 'hollows' or what we would say in current day vernacular, the holes (a hollow was a type of hole).  (it also means the walls are lighter so the foundation needs are different)

Frog bricks were moulded bricks where each brick is cast in a mould by hand.  These aren't hollow as the frog - or depression - only goes in a fraction of an inch and is filled entirely with mortar.  So there aren't any hollows (air gaps) when they are in the wall.

Wire-cut bricks usually didn't have a frog and although they took less labour to make, my grandfather hated these as they made it more difficult to get the wall to not fall down.  

(again, this is according to my grandfather's opinions which may or may not agree with opinions of other bricklayers)  

Luke Mitchell wrote:Then there are these bricks, with several holes that go all of the way through them. This would serve as a key, of sorts, for mortar but I suspect there is a different use for these (such as rebar, suggested by Thomas). I think this type of brick would have reasonable insulation properties too.

Thanks, Luke. Those are the type of bricks I'm talking about. I think mine have even more holes, like the image here.

Anne Miller wrote:Do you have a fireplace that goes with that chimney?

This sounds like the perfect place to set up a Liberator (rmh.)

The upstairs fireplace was retrofitted with a natural gas insert. It's not all bad, since it keeps the sitting room cozy without the need to run the big natural gas furnace for the whole upstairs.

The downstairs fireplace is original. I plugged the flue with insulation to keep it from vacuuming heat out of the house. I have considered installing a high quality wood insert, but insurance is giving me a big hassle about it. And unfortunately, the location is lousy for heating the house on a continuous basis.  

I do keep an old wood stove and piping in the garage in case I need to adapt it for emergency heat to protect against freezing.

How would those hollow bricks work as pavers? A recent landlord had paved his garden walkway with those, but placed them on the side for some unfathomable reason. When I took over the area a decade later they were flaking away like crazy, little clay shards all over making it a pain to be barefoot. I wondered if these were somehow formed to withstand compression when the holes were upright and might not break up if placed in the path that way. They could make a good porous surface to allow quick drainage (as long as the earth in the area wasn't heavy clay) while providing a solid surface for foot traction...

Coydon Wallham wrote:How would those hollow bricks work as pavers?

I tried that once, with a flat of free hollow bricks.

In no time, the bricks were covered in weeds, moss, grass, growing through the holes. It was impossible to maintain a grippy brick path.

Based on my experience, I think they may be ideal for a hydroponic greenhouse operation.

Bricks are made out of clay and firing techniques to be in walls.  Up off the ground away from moisture.  

Bricks for the ground are made differently.

I don't know how differently.  But I imagine moisture plus freezing and thawing would make them crumble much faster than paving bricks.  

I distinctly noticed they all flaked off in sheets parallel to the holes. I figured they were produced by being extruded or compacted in such a way to have greater strength in the direction they were supposed to be stacked to support weight. I guess even if that were so that they wouldn't necessarily be strong enough to take much traffic.

Despite being in the ground, I didn't notice many of them that had cracked at the holes like it was from freeze thaw cycles, they were mostly flaking off at the top (side) as they were being walked on.

thomas rubino wrote:My understanding is the holes allow rebar to be placed.

I was hoping this would be the case with the free bricks I just picked up. They are what I've seen in the past with three big holes roughly centered across the brick. Unfortunately when I stack them up, the holes do not align in a helpful pattern. I'd assume if holding rebar was a primary consideration, the holes would be placed to line up when in a normal overlapping pattern.

As I intend to use these as walls on a 'pebble style' RMH, I'm now hoping the ~1/2" gaps between bricks needed to have the holes line up for rebar will be small enough to retain the fill...