Chris' Corner: Here a crack, there a crack (part 6)

Here a crack, there a crack (part 6)


Russel Ray is a very professional, knowledgeable and experienced home inspector from San Diego CA and fellow Active Rain blogger.  Over the last while, he has written a series of posts on the subject of cracks in a property.  If you have a crack and are unsure of the impact on your property, consult with a professional, such as a structural engineer, however, as a primer, and to gain general knowledge, I have found Russel's information very helpful.  This is Part Six of the series and here Russel discusses cracks in raised foundation that start at an opening in the foundation.  There are many excellent examples with photos of different foundations with different issues ...


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Here a crack, there a crack....
(part 6)

DISCLAIMER: This discussion is based on several decades of experience in real estate, including as a home inspector and general contractor. I am not now a concrete professional or licensed structural engineer, so if you are not comfortable with common concrete cracks and our discussion here, hire one of those two professionals to help you. This discussion, however, should help you be a little more knowledgeable about cracks so that you don't just automatically assume the worst. Cracks happen, kind of like ActiveRain blogs.

I'll presume that you have read previous lessons.


Lesson Six

So far, we've discussed

  1. curing and shrinkage cracks in the foundation stem wall in the garage (Lesson One and Lesson Two),
  2. cracks in the garage floor (Lesson Three),
  3. cracks in the foundation stem wall of the house proper, the living area (Lesson Four), and 
  4. cracks in raised foundations with crawl spaces (Lesson Five).

Let's continue with raised foundations with crawl spaces, particularly the effects of water and ventilation of the crawl space.

Figure 1 shows a crack on the outside of the foundation, at a crawl space vent.


Figure 1. Raised foundation crack at vent


You can find similar cracks at the access opening to the crawl space. That type of crack is extremely common and, all other things being equal, is not of a structural concern. One would want to double check the interior of the foundation, as well as the interior floor, wall, and ceiling in that location, to make sure that all other things are equal — 99.9% of the time they are.

When you put a hole in a hard material, excepting perfectly round holes, the stresses in the surrounding materials will be focused at the corners. That's why round holes and semi-circles are so structurally sound and why you see them in arches that are thousands of years old and still holding up very well, all other things being equal.

Figure 2 shows a crack on the interior of the foundation wall that is a little more problematic.


Figure 2. Cinder block wall


We learned in one of our previous lessons that cracks like to follow the path of least resistance. Normally the path of least resistance in a cinder block wall (concrete masonry units, or CMU's) will be the filled-in mortar joints between the blocks, so if the crack blasted through the  the mortar and the blocks, well, "Houston, we have a problem."

Note that the crack in Figure 2 is a vertical crack, and it was a vertical crack in the garage foundation stem wall that started this whole discussion (see Lesson One). That crack in Lesson One was not a problem due to its location. The crack in Figure 2, though, is a problem. The important point here is that not all vertical cracks are equal. Where you are (garage or crawl space) and what the cracked material is made out of (concrete or cinder blocks) are also important.

Figure 3 shows a wall that is not only cracked, but excessively deteriorated.


Figure 3. Cracked and deteriorated foundation wall.


Deterioration such as that in Figure 3 typically comes from an excessive amount of exposure to water, and since we don't have a lot of rain here in San Diego, the logical culprits are lack of gutters on the roof and a lawn irrigation system that is either watering the foundation or overwatering the property so that the soil near the foundation becomes constantly waterlogged.

Figure 4 shows the interior a foundation crawl space, the same foundation shown in Figure 3, although a few feet away.


Figure 4. Exposed concrete aggregate.


As you can see, it does not look as bad as the exterior. See the difference that water makes?

However, when you can see the aggregate (rocks) in the concrete, you've got problems that need to be addressed, especially before you go remodeling the interior of the house, and double especially if you plan on putting tile on floors or bathtub/shower walls. A significant exception is over in the East where many buildings have rock foundations. The difference is that those rocks tend to be huge whereas aggregate rocks are small. Does anyone reading this have a picture of one of those eastern rock foundations that you can leave in a comment?

Just about anything thrown into a pool of concrete will make the concrete stronger. Dare I say that the foundation on my uncle's house in Riviera, Texas, has a lot of Schlitz, Pearl, and Budweiser beer cans in the foundation? We built his house in 1973, and it has successfully made it through several hurricanes (Allen, Gilbert, Bret) and tropical storms that roared through South Texas.

Figure 5 shows a foundation that pretty much doesn't exist anymore. That whole corner of the house was sloping with multiple interior wall and ceiling cracks.


Figure 5. Failed foundation.


The type of water damage shown in Figures 3, 4, and 5 will result in sloping floors, cracked floors, squeaky floors, cracked walls, and cracked ceilings. That I can guarantee you.

There are basically two ways to prevent excessive water damage to a raised foundation:

  1. Provide ventilation for the crawl space. Very good ventilation. If you walk around a house built on a raised foundation, you'll vents every few feet like that shown in Figure 1. Adequate ventilation allows the interior of the foundation crawl space to air out, so to speak, preventing moisture from becoming trapped in the crawl space.
  2. Protect the foundation from moisture. Remember the luxury crawl space in Lesson Five? Here it is again:


Figure 6. Protected crawl space


What the homeowner of the property shown in Figure 6 did when he renovated the property was to replace the foundation walls, enveloping them in 52-mm polyethylene to protect them from the soil. Then he laid more polyethylene on the ground and installed a concrete slab on top of it. Next he sealed the foundation vents, plastered and painted the interior of the crawl space, and installed an air removal system (the silver duct, top middle). That provided an interior crawl space that is almost completely sealed and should make the foundation last many, many years longer. Odds are that it will never look like the foundations in Figures 3, 4, and 5.

Figure 7 shows a homeowner repair of a foundation.


Figure 7. Homeowner repair


I use the term "repair" very loosely. Generally, a bunch of rip-rap around a deteriorated foundation isn't going to do anything other than simply ugly.

As always, if you are not comfortable discussing common cracks, hire a professional to help you.

Join us soon for Lesson Seven. 


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Comment balloon 0 commentsChris Smith • April 20 2011 02:29PM