Over the past couple of months I have had occasion to inspect two or three houses with structural problems, which may be more common than I had ever imagined.
One house I visited had a crack up an outside wall, which stretched out onto the roof. The crack up the wall was visible from both inside and outside the house. When we removed the plaster on both sides of the wall, we saw that the brick in the wall was broken and the wall had separated from one column by the width of a pencil lead. The crack on the roof was much smaller, but large enough to allow water in.
At first I suspected that the column had settled over the years and had simply broken away from the rest of the house. However, this was not the case. What had really happened was that the house had been remodeled several years ago and when a new room had been added to the original structure a new dala (beam) had been poured. When the albañil tied the new dala into the old column he had not been so industrious as to open up the existing column enough to actually tie the new rebar into the old. What he did instead was to make a hook with the new rebar, and place that around the old rebar in the column. With time, the cal in the concrete mix deteriorated or washed out leaving room for the hook to "slip". The slippage gave the dala room to move which caused the bricks in the wall to crack and the roof to start to leak.
The solution was to simply weld the rebar in place so that the dala was once again an integrated whole. Once that had been accomplished, we could replace the plaster and patch the roof. Fortunately, this problem was discovered before it got any worse. The wall was still plumb and the roof could still be patched. If the problem had been let go for another year or so, the solution would not have been so simple and way more costly.
If dalas in the form of rebar embedded in concrete or I-beams do not form a complete unit with columns, both at the top and bottom of a wall, then post-and-beam construction will develop structural problems. It's the steel in the structure, which holds the whole thing together.
Another problem I have encountered recently is the I-beams in a roof not setting on some sort of steel, but rather just setting on a brick in the wall. When a boveda roof is formed, I-beams are set approximately one meter apart, then the brick is arched between the I-beams to form the boveda. Those beams actually carry a fair amount of weight and are, at the same time, subject to certain horizontal stresses from the arch in the brick. In other words, those I-beams want to move. For this reason they should be welded to another I-beam, or to the rebar in the dala. They should not be stuck through a brick wall without steel support of any kind. If they should rest on a brick in the wall, you can be sure that they will move over time. It is most likely that they will move straight down. It takes time, but the movement is unstoppable. As the beam moves downward, a crack will develop in the roof and water will find its level.
To solve this problem it is most usual to chisel out a portion of the wall and install another I-beam under the errant roof beam. The new I-beam needs to be welded into columns on both sides of the beam to provide support. Then, the whole site can be plastered over and forgotten.
Anytime new construction is being added to old construction, care must be exercised to assure that the new is tied or welded into the old. Failure to do so will result in non-integrated wholes, which run the risk of becoming rubble.
Mr. Worthington is a long-time resident of the area, a builder and landscape architect. You can contact Mr. Worthington at: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
