Retaining wall Autopsy

What we have here is 20 year old landscape masonry which has failed.  Some walls are leaning where corners have broken.  In other places they bulge where the mortar joints cracked and the visible portion of the structure is slowly sliding away from the buried half. The footing appears to be in good shape as there is no sagging or signs of settling. Overall the mortar is in fairly good condition, the wall just wasn’t up to the job.

It is my opinion that water destroyed this wall. More specifically, trapped water due to poor drainage. Freezing can cause similar damage when water freezes and expands exerting additional force. I am fairly certain that this was not the case here as the plants in the planters would not have survived. Also water can be seen seeping out of the broken spots.

The importance of proper drainage in retaining wall construction cannot be overemphasized.  A retaining wall or in this case a raised planter is a container designed to resist a certain amount of force. For example a paper bag is a container designed to hold a load, but if you over fill it, the bottom falls out.  Luckily paper bags are cheap and easy, brickwork is slightly more involved.

Back to the Rain…

So ends a beautiful stretch of spring weather. Imagine feeling like it’s July in April. But now it is back to the rain, the weather Seattle is most renowned for. This weather often reminds me of masonry problems, as many are water based.

Now imagine a bathtub full of water and you open the drain (assuming the drain is clean) that is a lot of water going through a relatively small hole in short order. This example is difficult for me because I get hung up on the fact that water weighs eight pounds and some change per gallon, pressure, velocity losses of the pipe etcetera. It just doesn’t translate well into the way water enters a masonry structure. But the fact remains that you can get a lot of water through a small hole.

So how does water get in? (and what you can do about it)

1)      Down the chimney unless you have a cap installed. Seems like a no-brainer, but it is a commonly overlooked item. Take a look around Ballard, Madison Park, or Queen Anne and see how many chimneys have caps. My own chimney went forty years before it got capped. A puddle in your chimney can soak into porous mortar, transferring moisture into your house, and also greatly reduces the service life of your chimney.

2)      Through defective, improperly installed, or missing flashing. Although flashing (and associated problems) are not unique to masonry construction alone, it is nevertheless a very important part of a masonry structure. Flashing is especially critical around chimneys (roofs are very wet places), but is also important on lintels and copings, really anywhere there is a ledge for water to sit on there should be flashing to keep water out of your house. When water gets around flashing and enters the home, it can lead to mold and mildew problems and rotting wooden framing.

3)      Water can also enter through cracked or missing mortar and bricks. Remember that bathtub? A lot of water can get through a small hole and it doesn’t just rely on gravity to get there, strong winds can blow rain sideways. That is why tuck pointing (the process of removing and replacing old, failing mortar to weatherize a structure) is such an important maintenance step to keeping your home dry. Once water gets into masonry walls it absorbs into brick and mortar leading to more cracks holes and broken bricks… and more water coming in.

4)      Porous masonry materials act as a sponge drawing water into your home. Poured concrete is notorious for letting water in, especially in poorly homogenized areas where you can see a lot of rock and gravel. It is not unheard of for streams of water to run from such spots. Concrete Masonry Units (C.M.U.) or as I like to call them “concrete blocks” also absorb water. While mortar joints have the same problem it is not an issue if they are in good repair and properly struck. Mortar joints are struck (shaped) in a generally concave manner so they are not directly exposed to rain. Because concrete absorbs water it is important to waterproof it using sealers and other means.

Stay dry.

Brick Masonry

When it comes to masonry choices, the three most popular are slump stone, new brick and manufactured alternatives.

Bricks

Brick is made of fired clay and comes in hundreds of different colors. Considered by many to be the ultimate exterior wall finish, brick contain many advantages.

Readily available most everywhere with thousands of varieties to choose, brick is one of the most durable building materials. In fact, brick masonry should last 100 years, with the first 25 years completely maintenance-free.

Brick also won’t catch fire, rot or be eaten by termites.

It can be one of the higher-priced exterior finishes; however, many homeowners prefer brick because, due to its durability, it’s less expensive in the long run.

Stone

Stone is another attractive, durable and expensive choice. An antique form of masonry, stone will last a lifetime. Just check out all the Greek and Roman monuments still standing today!

Unfortunately, stone isn’t as available as brick, and not every stone works for masonry work. Some types of stone are too soft, and others are too porous. Stone exteriors also work best when installed with old-fashioned techniques.

Water is stone masonry’s worst enemy because freeze-thaw cycles can cause cracks. Properly sealed stone masonry prevents problems.

Every year, check your building’s masonry exterior four hours after a heavy rainstorm. Any dark patches on the wall means that water soaked into the surface. This is a future problem that will need fixing.

Manufactured Brick and Stone

There is a third alternative to brick and stone which contains all of the above advantages at a lower cost.

Many times what appears to be stone or brick on a house is actually a lightweight concrete-manufactured stone veneer or cultured stone.

A mixture of Portland cement, natural aggregates and iron oxide pigments is poured into molds made from real stones. The result, available in a broad palette of colors and styles, looks incredibly realistic.

Architectural blocks are another attractive, virtually indestructible option. These are essentially the same as conventional concrete blocks, except they resemble polished granite, look like hand-hewn stone or tile or have other decorative finishes.

Concrete block masonry is more common with industrial buildings. It should last 50 to 80 years, and you’ll need to fix the joints after 25 years.

Unlike brick, concrete blocks are not waterproof. You’ll need to apply a water seal every 10 years.

The best water seals are silane and siloxane. You can apply them by spray, and they soak into the surface of the wall like stain.

Article by Service Magic
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