Forums > Specific Focus > Home, Garden & Construction in Mexico

D.G.

Sep 9, 2003, 1:19 PM

Post #1 of 6 (3599 views)

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Cracks

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Since masonry construction is the dominant type of building in much of Mexico, and since I come from houses made of wood frame construction, I was just wondered what is the recommended method of fixing a wall with cracks in it. If we buy a house that has (or develops) cracks, I'd like to know what to do.

Thanks.

Rolly / Moderator

Sep 9, 2003, 2:40 PM

Post #2 of 6 (3591 views)

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Re: [D.G.] Cracks

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Plaster cracks in wood frame construction are fairly common due to the flexing of the wood frame. That is why gyp-board has largely replaced plaster walls. Masonry construction is much stiffer, so cracks caused by structural flexing are uncommon. Hair line cracks sometime occur in the plaster on a ceiling/roof because of thermal flexing of a thin roof. Generally, any serious cracking is indicative of a structural problem which probably needs to be examined by a professional.

It is very likely that plaster cracks are not going to be a problem in your home in Mexico.

Rolly Pirate

TomG

Sep 10, 2003, 9:25 AM

Post #3 of 6 (3573 views)

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Re: [Rolly] Cracks

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Rolly, I was in an newly built (one year old) owner-built adobe house in a pueblo outside Oaxaca which was stucco outside and plastered inside (I assume the these were the materials and were in that order). What I noticed inside is that the plaster finish was riddled with an equally distributed craze of tiny hairline cracks (1 -2 feet in length maybe) that were all open about the same amount - maybe a few thousands of an inch, pretty tight. I thought they maybe were stress pattern cracks resulting from material shrinkage after construction. The coefficient of expansion of plaster is rather close to nothing compared (which is why it is a good molding and pattern material). My assumption was the fault was in the adobe (clay has a great amount of shrinkage). Even if the adobes were quite dry the bedding mud would introduce a lot of moisture. But that would all lead to shrinkage - not expansion. If the plaster were put on too soon, the direction of the force should have been toward compression of the plaster (pulling it together so to speak).

Anyway, my thoughts were that the craze cracks were representing the opposite of what forces I could imagine could have been in play. Nothing was structural, but I thought it presented a construction materials problem I would not have thought of.

Whaddaya think?

Rolly / Moderator

Sep 10, 2003, 11:50 AM

Post #4 of 6 (3562 views)

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Re: [TomG] Cracks

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Interesting question.

I don't have any experience with adobe, so I don't know why the cracks formed as they did.

Rolly Pirate

Esteban

Sep 27, 2003, 3:48 PM

Post #5 of 6 (3516 views)

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Re: [D.G.] Cracks

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Personally, I've never seen anything built of concrete that doesn't have cracks. In the US, I have used a combination of concrete impregnated with chopped fiberglas for garage floors so that the cracks don't appear. Concrete cracks aren't necesarily structural in nature. The steel in the concrete expands and contracts at a different rate than the concrete itself as does the rock in the concrete as does the ground under slabs and footings as well as walls at different levels. All this expansion and contraction causes mostly surface cracks because the finish on concrete walls is made of a substance of virtually no structual value. I have determined, from experience in this field that having a good roof, good surface drainage and with the proper finishing techniques, including sellador and a plethora of other typical Mexican alchemy by a good maestro, your cracks will be kept at a minimum. I am not saying that all cracks are benign but that I wouldn't worry too much unless you see a large separation or a crack enlarging quickly.

TomG

Sep 30, 2003, 7:45 AM

Post #6 of 6 (3492 views)

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Re: [Esteban] Cracks

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I'm a believer in using fibers in the concrete, as well. But I have long been of the belief that the marriage of concrete and steel is one of the most compatible and complimentary combos in construction materials. That they expand and contract at the same rate, and that concrete prevents steel rust except were sea water is used in the mixing.

Your emphasis on good roofs and good drainage is wise construction advise in all environments.

I had no idea that the aggregate in the concrete expands differently than the mix. Although I can see where the ground, footing and walls might act independently.

These construction questions are interesting. The sad part is how a faulty analysis of the these interactive conditions can permanently compromise a building. Yet on the cheery side how many compromising conditions a house can have and still serve faithfully for generations.