Rubble is a fixture of most construction sites. Rubble is a fixture of most construction sites.

Rusting concrete rebar is a hidden danger

Cracking plaster in the ceiling? Be careful the roof doesn't cave in

Second of a series entitled The Joy of Construction in Mexico, chronicling the writer’s first steps as a home inspector in Mazatlán.

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Becoming a home inspector in Mexico presented a number of unique challenges. The process of inspecting a house required knowledge of local construction methods along with understanding the causes of deterioration or failure of the building components.

So I formulated a training program for myself that included internet research coupled with visits to homes under construction. It was on the visits to ongoing construction projects where I experienced a certain measure of entertainment, which was tinged with a bit of horror.

But first let me give the reader some basic information about homes constructed in Mexico.

Homes built here in Mazatlan, along with many other parts of Mexico, are constructed with reinforced concrete post and beams with a brick and mortar infill over a concrete slab. Ceilings, roofs and suspended floors are reinforced concrete slabs approximately three to six inches thick.

An insulated roof/ceiling is fashioned with a grid of reinforced concrete with 10 to 12-inch-tall polystyrene blocks filling the spaces created by the grid. Any plumbing or electrical requires a channel cut into the brick and across the concrete posts and beams to properly bury the conduits and pipes in the finish plaster.

When I observed the first few construction sites in action, I could not help seeing them as a theater of the absurd. After all, I had only been in Mexico for a year and at that stage I retained much of my “north of the border” persona.

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I soon learned that most laborers demolish old walls, or old houses, with 12-pound sledge hammers while wearing huaraches that most people would have discarded years ago. It is not uncommon to find everyone on a construction site wading through rubble, bricks and tangled pieces of rebar because no one feels responsible for any meaningful clean-up on a regular basis.

All the escombro (rubble) is hauled in five-gallon buckets because wheelbarrows are unable to navigate the chaotic site. I soon realized that safety was not a concern in Mexican construction.

As the new construction moves forward, piles of sand, gravel, bricks and bags of cement sprout on the sidewalk or street in front of the project. From this point forward, a night watchman is on site to prevent the theft of the aforementioned materials.

When the time comes to form up the roof or second floor, a crew arrives with a large truckload of wooden pallets and small-diameter, tree trunk poles. With the poles as support, the pallets are joined to create a platform for the elevated concrete slab. Since none of the poles are the same length, small scraps of wood, or bricks, or rocks, are used as shims in an attempt to level the elevated forms.

Once this maze of poles is complete, a grid of reinforcing steel is assembled and dropped on top of the pallet platform. It is then followed by the concrete.

I am sure I could ramble on for several more paragraphs, getting into more construction detail; however, I refrain from such discourse so as to prevent my readers’ eyes from rolling back as they slip into a state of bored torpidity.

After getting the general gist of the construction procedure I spent time talking with people who had purchased homes and had dealt with a variety of problems. I also did a walkthrough of a couple of older houses that were currently on the market.

Electrical problems topped the list of severe problems, with cracking plaster a close second. Plumbing and water problems, including flooding, were also high on the list but I pass over these for the moment. Since I came from a world of stick-framed houses, and my electrical and plumbing knowledge was extensive, I needed to work to understand why almost all older houses had cracking plaster problems, which seemed incurable.

When I examined walls and ceilings where the plaster had failed and sloughed off in large chunks, the exposed rebar was incredibly rusty and flaking. Obviously, moisture was getting into the reinforcing steel inside the wall or ceiling, causing it to rust.

This rusting causes the steel to expand during the oxidation process and the expansion was cracking the plaster. This revelation meant that carful roof inspections were a critical component to any of my future home inspections.

Sure enough, after my first 20 or so it was patently clear that a poorly sealed roof or parapets could cause plaster damage in ceilings and walls. Even if a faulty roof has been fully resealed and the plaster patched, the cracks will return in time.

The persistent cracking is because the oxidation of steel is a chemical reaction, which will continue unless it is abated chemically with phosphoric acid.

Several years ago, a gringo bought an older home here in Mazatlán. It had been recently renovated by the Mexican owner. After about a year, a few small cracks began appearing in his bedroom ceiling, and slowly started growing and joining.

While he was in the States for a few weeks, his bedroom ceiling experienced an instantaneous, catastrophic failure, which relocated 1,000 pounds of plaster to the floor in less than a second. The bed, the nightstands, a dresser and a couple of chairs were completely destroyed.

While viewing the wreckage with the stunned owner upon his return to his beloved home, I noticed a number of orange spots around the rusty ceiling rebar, now exposed by the collapse. Apparently, when this ceiling had failed the first time, someone had painted the rusty rebar with rust inhibiting primer thinking it would halt the oxidation process. It doesn’t. The gringo was fortunate to have been away from home rather than in his bed at the moment of ceiling failure.

A couple of years ago a gringa friend rose from her chair under the concrete awning of an old property now hosting a popular restaurant along the malecón. As she moved away, calling for the bill, a sizable chuck of concrete took away the edge of the table where she had been leaning and fell through the seat she had vacated.

Recently, a friend showed me the remains of her cat’s food bowl after a large piece of ceiling lost its battle with gravity. Such events are common here.

As a consequence I highly recommend that anyone living in an older Mexican home in areas where building practices resemble those used here undertake the yearly exercise of using a broomstick or pole to tap as much of the ceiling as possible to find the hollow spots that could foretell future problems.

In my next column I will delve into the electrical mysteries lurking in Mexican homes, including the Case of the Toasted Geckos.

Bodie Kellogg describes himself as a very middle-aged man who lives full-time in Mazatlán with a captured tourist woman and the ghost of a half wild dog. If you wish to give him cold beer, large sacks of money or a piece of your mind, he can be reached at buscardero@yahoo.com.

Stories from our archives that you might enjoy

  • TioDon

    3rd world country…

  • DeplorableVI

    Years ago Florida had a problem with exploding rebar on many highway bridges. Apparently they used Beach sand in cement mix and the salt reacted badly with the stell rebar.

  • Andrew Green

    Thank you very much for this, and your previous article.
    I’ve been impressed at how resilient the basic technique in Mexico has seemed to be in the face of earthquake and other insults. But it does seem to be more about habit than conscious design, so if there are small changes in technique that could be suggested and encouraged, then life here would be improved.

    • 68gomat

      After my removing the roof of my Mexico house and adding 2 more floors with a family of albaniles(bricklayers) they were impressed with how I put all the electrical and plumbing into the block, cardenas (beams), castillos(posts), and bovedillas as the walls went up. Once the stucco was finished the whole house was already roughed in. I’ve seen their subsequent projects using the same ideas. The albaniles don’t like to see all the holes hammered into the block and channels chiseled into the castillos and cardenas. We all learned something.

  • daniel pugh

    I await with anticipation and horror for your electrical piece. Having lived in Maz for 4 yrs, your stories takes me back to witnessing similar construction techniques. But my favourite is propping the ladder on 2×5 gallon pails to reach just a little higher. You just have to chuckle and carry on.

  • Stylez

    Nice write up.

    Can be a very dangerous thing especially when people sleep under bedroom ceilings for 8hrs a day. Odds can get rather big for cement to fall on a person.

  • Three score and ten

    Nice to know why I might get cracks in the ceiling, but it would be better to hear about a solution to the problem if I do.

    • Bodie Kellogg

      As stated above, treat your rusted re-bar with phosphoric acid before you paint it, and re plaster, it will halt the rust for a number of years.

  • Marty Rosenzweig

    Same problem along the southern Quintana Roo coast except the reason is some unscrupulous or incompetent contractors use brackish water for the concrete (from nearby cenotes). One guy actually used sea water! Another issue is unfinished structures with rebar exposed to the salty air sucks in corrosive water through capillary action. Rumor has it that Teflon coated rebar is now available in Cancun. At a price of course.

  • Kimberly Fleitz

    I have a home built between 19982 and 1984. We have also been under the ocean twice, Gilbert and Wilma. Every year I go around tapping walls and checking for expanding rebar. I have heard that there is a new cement compound that will alleviate the expansion of rust and allow me some peace of mind. I have never found it. Yes, living in the tropics is fun, and dangerous. I take 1/4 of the house a year, chip away at the old cracks and cement and repaint the rebar with anti rust stuff, put the cement back in. I am a widow, single, and tired of trying to learn about construction. Any recommendations? jajaja!

    • Bodie Kellogg

      Treat your rusted re-bar with phosphoric acid before you paint it, and re plaster, it will halt the rust for a number of years.

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