Traveling around Belize during the last couple of years, I have seen many concrete buildings – homes, churches, and
commercial buildings – being built using a concrete post and beam structural framework, with “fill in” concrete block
walls. This is an excellent construction technique, particularly in Belize – concrete building construction provides
protection from hurricanes, it is not affected by termites or rot, the materials are readily available, and Belizean
contractors are reasonably skilled in working with concrete and concrete blocks. But, more often than not, the “fill in”
concrete block walls in these buildings were not property reinforced. The walls were not tied into vertical structural
columns, did not have any of the cell cavities in the blocks filled with concrete, and did not contain horizontal or
vertical steel bar (rebar) reinforcement. While concrete block wall construction is an excellent building technique;
improperly installed, the wall may require costly future repairs and may put the building’s occupants at physical risk.
I live near a house that was built a few years ago. The rain water cistern providing domestic water for this house
was built using concrete block walls on an above ground concrete slab. The concrete block walls containing the collected
rain water were not adequately tied to the cistern’s floor slab with vertical rebar nor were the block walls built with
adequate horizontal or vertical reinforcement. So what? Water is heavy and when stored it exerts pressure horizontally,
as well as vertically. What this means is that water wants to escape its container, anywhere it can. In the case of this
cistern, the builder initially wrapped the exterior of the cistern with steel bands to hold the concrete block walls
together. In less than three years, these same block walls needed to have additional exterior steel bands installed to
prevent the cistern from “exploding”. If the concrete block walls had been properly installed at the start – adequately
tied to the concrete cistern floor, properly tied at the building corners, and installed with adequate vertical and
horizontal reinforcement – the walls would not have required the additional costs of exterior banding to keep it from failing.
OK, you agree that cisterns might require special consideration but why worry about normal building walls? We have
neighbors who are adding a second story master bedroom to their home. Prior to Hurricane Dean, they had the structural
concrete column corners and some of the concrete block “fill in” walls raised. These concrete block “fill in” walls were
neither adequately tied to the floor slab or corner columns, nor did they contain adequate vertical or horizontal reinforcement.
After Hurricane Dean passed many of these block walls had been blown down. Had these walls been installed properly the owner,
most likely, would not be paying twice for the materials and installation of these walls. Worse, had these walls been completed
and if people had been in the room during the hurricane it is possible that there may have been injuries to the occupants.
The solution to these problems is fairly straight forward. All concrete block walls must be properly anchored to the foundation
beam or floor slab upon which they are installed. To accomplish this place a rebar “L” in the rebar cage of the foundation beam
or floor slab where the cell of the first block is to be placed and continue placing L’s in the location of every third or fourth
cell in the wall being installed. As the wall is raised, each cell with an L anchor should have additional straight rebar lengths
placed in the cell and secured to the rebar below it and the cell filled with concrete. If not otherwise located as described,
vertical core-filled cells with rebar should also be placed immediately adjacent to all vertical structural columns and all window
and door openings. Concrete block walls for cisterns and septic tanks should have every cell filled with concrete, in addition to
properly designed vertical reinforcement. Vertical reinforcement is intended to resist flexural stress on the wall, as well as
impede propagation of small cracks that inevitably form in concrete. Horizontally, every second or third layer of block should
have rebar or wire mesh or other horizontal joint reinforcement placed in the mortar layer between the blocks. Like the vertical
reinforcement, this horizontal reinforcement is intended to resist flexural stress on the wall and impede crack propagation. At
the junction of each block wall with a concrete column the wall should be tied into the column with the wall horizontal rebar
extending through the vertical rebar cage of the column. Similarly, if the concrete wall abuts a steel column or wood pier,
the horizontal reinforcement of the block wall should be properly tied to the column or pier with properly designed connection
details appropriate for the vertical structural material involved. Finally, at building corners that do not involve columns and
at wall-to-wall interdivs, the horizontal reinforcement of each adjoining block wall should be tied to the abutting block
wall with horizontal rebar extending from the reinforced horizontal joint of the joining wall.
Don't Build Your Cistern Out Of Block!
I have to take issue with a couple of items in the Building With Concrete Block article. First, IMHO, building a cistern out of block, no matter
what reinforcement that is used, is nuts! It is a particularly bad practice here in Belize, given the suspect quality of the blocks available. In ground or above ground, it is cheaper and easier to just build the damn things
out of 6" steel reinforced concrete!
I also haven't seen any advantage to horizontal reinforcement of non-bearing block walls, except at the corners and columns. I've seen a
lot of hurricane damage, and horizontal steel in the walls made little or no difference.
I agree with you totally that a poured, reinforced concrete wall for the cistern is a much better way to build. Unfortunately, it is not
the typical approach here. You have a valid point regarding horizontal steel...definitely at corners and columns as you point out.
The primary benefit in non-hurricane loading is that horizontal steel helps mitigate the cracking at mortar joints and stucco surfaces
during normal weather related wear and tear. Its use is a cost trade off with long term maintenance.
A reader has other issues:
I have just read your article "Block Construction" published on John's "Consejo Belize" website.
I am sure that the following paragraph refers to my master bedroom and, if it is, would like you to have it deleted from the
article in its entirety as it infers that I do not have any consideration for the safety of my family and have no knowledge
of block construction.
"We have neighbors who are adding a second story master bedroom to their home. Prior to Hurricane Dean, they had the structural
concrete column corners and some of the concrete block “fill in” walls raised. These concrete block “fill in” walls were neither
adequately tied to the floor slab or corner columns, nor did they contain adequate vertical or horizontal reinforcement. After
Hurricane Dean passed many of these block walls had been blown down. Had these walls been installed properly the owner, most
likely, would not be paying twice for the materials and installation of these walls. Worse, had these walls been completed and
if people had been in the room during the hurricane it is possible that there may have been injuries to the occupants."
Vance, I am a DYI enthusiast, not a professional construction engineer - although during my time as Plant Engineer for the Belize
Estate and Produce Company one of my responsibilities was for the maintenance of all the Companies buildings.
If you look at the picture below, taken immediately after Hurricane Dean passed, you will notice that, contrary to your article,
there are no columns. You will also notice that the walls are 6 blocks high and that there are saw cuts in the tops of all the
blocks, which were to be knocked out to accommodate 1/2" rebar. You will also see that the centre column concrete would also fill
into the half blocks on either side of the wall. The walls were tied into the corner columns with 1/4" hooks at every second block.
R.F.Greenwood, probably the most famous Civil Engineer in Belize, shows, on page 70 of his "Hurricane Resistant Construction" * book,
an alternative method of reinforcing concrete blocks, which makes block laying a lot easier than your method.
However, whatever method is used it cannot be effective until it is completed and it was just unfortunate for me that my construction
was subjected to 120 - 160 Mph winds before it was ready to withstand them.
I am copying this email to John to make him aware of the situation.
* Alan has a copy of this out of print book that he graciously has agreed to lend to anyone in Consejo Shores who is interested.
I have no interest in getting into a confrontation with you. The article I wrote was intented to be and was written as a compendium
of concrete block construction problems I have seen over time in various parts of Belize. I made no specific reference to your house
or any other building structure in the article. In fact, as you note, the building described in the paragraph you cited is not a
structural description of your house.
The article that appears on John's website was previously approved and published by the Association of Professional Engineers of Belize.
I have no intention to alter the article. However, I have forwarded this note to John and if you and he wish to delete the article from
his private website that is John's perogative.