Wednesday, November 8, 2017

Making a small concrete block masonry building

This material is based upon work supported by the National Science Foundation under Grant No. 1660075 ("Topological interlocking manufactured concrete block").  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author, and do not necessarily reflect the views of the National Science Foundation.

Today I'm taking a look at the construction of a small building assembled from manufactured concrete block.  This particular building was made to serve as a kiln room.  A kiln is a high temperature oven or furnace used to heat (fire) ceramic material.  Kilns may also be used to melt metal, or glass, or for any heat-treatment of materials, such as drying green wood.

This building has a footprint of around 14 feet by 12 feet, or around 170 square feet.  There is a trend today toward "tiny houses" where people are attempting to live in such small spaces.  Personally, I don't mind living in a small house (under 1,000 feet is OK) but I would not care to live in such a small space as this: it is appropriate for a shed, or a safe room, or even a kiln room.

A "safe room" is an appropriate use for a building this size.  A safe room like this would be appropriate to survive a tornado, or hurricane or wildfire.  The need for an affordable, high-strength, fire-proof safe room has been brought into sharp focus over the past few months, with the arrival of hurricanes Harvey, Irma and Maria; and also with the devastating wildfires in California and across the American West.  A building such as the one shown here would allow people to survive any of these disasters, providing safe refuge in the face of any of these natural disasters.  Many residents of Texas, Louisiana, Florida, Puerto Rico, US Virgin Islands, and California would have benefited from one of these structures during the hurricanes and wildfires which impacted these areas.  A structure such as this provides an affordable solution to these natural disasters, and gives people a safe place to survive these devastating type of events.

Following are some photographs showing the construction of this building.  The vertical walls were made with standard 8 inch x 8 inch x 16 inch concrete blocks, or "cinder blocks" as they are commonly known.  The side walls of this building include blocks which are oriented with their long dimension oriented at a right angle to the wall, creating a series of vertical buttresses, or pilasters for additional strength and reinforcement.  These blocks have hollow core holes which were subsequently poured with grout and also contained a series of vertical rebar for additional reinforcement.

Here is the building site before construction began.

Construction has begun, a few hours into it.

Vertical walls almost completed, this took 2 days to build.

There were 450 regular 8 inch x 8 inch x 16 inch block used to make all of the vertical walls.  These block cost $1.20 each.  There were 30 8 ft. pieces of rebar used in the hollow vertical cores of the walls, which were poured with grout.  I used "gatorbar" rebar, made by Neuvokas Company.  This rebar is made from basalt, which has a very high tensile strength and will never rust20 foot long pieces of this rebar cost around $5.50.  The grout cost around $30 for the entire structure.  Mortar for the entire structure cost around $45.00.  The material cost of these vertical walls (including block, mortar, rebar and grout) was around $700.

This shows wooden forms used to make arches between the vertical buttresses or pilasters.

Here are wooden forms used to make a concrete skewback, from which the masonry arch roof is built, or 'sprung.'  

This shows the arch assembly as it begins.  Note the use of 'gatorbar' rebar used to help create the arch.  This block is described in more detail here.

Here is the masonry arch being constructed.

This shows threaded anchor bolts (3/8") which were used to attach a wooden covering to the roof.

This is the 3/8" anchor bolt, which is inserted into the mortar beds between blocks of the arch.

Here is the building with a completed masonry arch.  This could have been made waterproof with any number of techniques, including waterproof paint, rubber roofing, etc.  I try to use the most common construction practices, methods and materials: so I used a wooden surface, covered with tarpaper and then finally covered with shingles.  Any of these methods will work.

Here is the wooden roof surface, covered with tarpaper.  Note the stainless steel chimney for the kiln in the back.

Here is the shingled building, more or less complete.  I will still install a door, and I may paint the building with a waterproof masonry paint, such as (for example) Drylok(TM).

This building represents a simple, high-performance, inexpensive approach to providing a very safe structure capable of withstanding wildfires, tornadoes, hurricanes, and other extreme weather events.  The cost of materials for the vertical walls was around $700.  The cost of the masonry arched roof was $644 in block, around $70 in mortar, and $77 in rebar for a total material cost of $791.  The total material cost of this building was $1,491.  This material cost does not include labor, and labor costs vary widely.  This was built by two masons working for 5 days, 8 hours each day.  By comparison, a smaller shed made of flimsy wood sheathing which is much smaller (8 ft. x 12 ft. vs. 12 ft. x 14 ft.) costs $2,199.  This wooden shed will burn, rot, suffer from insects, and is not nearly as strong: it would not survive a direct encounter with a hurricane or tornado.  There is really no comparison!  The wood shed costs $22.90 per square foot, the concrete building shown here costs $8.77 per square foot.

Upon completion of work funded by the National Science Foundation (Phase II, Small Business Innovation Research, SBIR) within the next 2 years, this technology should be accepted into the International Building Code and is expected to be available for sale internationally.  This small building is just another example of what this innovative masonry technology makes possible.  Better, stronger, safer buildings at a lower cost. 


  1. Arches should be for structural support, right? I'd like the whole idea but the design would be a bit better if the arches in the buttresses were above the concrete columns. As it was designed and built the arches are actually just hanging rather than supporting anything.

    1. Hi David, Thanks for your comment. Those little arches are part of a concrete skewback, from which the masonry arch roof is sprung. So those little arches between the vertical buttresses are actually supporting the masonry arch roof itself. They are not just hanging, they support the main masonry roof. They are poured with rebar in the concrete.