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7 problems with Allan Block concrete retaining walls you can’t afford not to know

December 11, 2020

DIY built retaining wall failing

Retaining walls can change your landscape from subdued to breathtaking, and can be the focal point of any space. They may seem simple in nature, but the physics behind them are way more complex than one might think. It is important to know the problems associated with retaining walls so you can be sure yours lasts for decades.

What are the biggest problems with Allan Block concrete retaining walls?

#1 Allan Block walls are usually not built correctly

It may seem like Allan block walls are easy to build, but most retaining walls you see are failing, or will fail, due to being built incorrectly. For a wall to be built up to standard, the same amount of soil that is excavated needs to be replaced. This is a lot of gravel, and can often be a step that is overlooked. Retaining walls take time to build properly, and should not be rushed to speed up the process.

So, if they are not built correctly what happens?

If a retaining wall is build incorrectly, they can have varying levels of failure, from minor separation between the blocks, to catastrophic failure where large portions of the wall fall over.

Retaining wall seperation

Bowed out retaining wall

While Allan block walls are a mortarless system, that are flexible in nature, and will not form cracks, however, poor design, installation method, or any other cost saving method will result in failure on some level.

Retaining walls are a big investment when built to best practices. Not only should they do their job of holding back hundreds of thousands of pounds of force, they should be straight, true, and an aesthetically pleasing center piece in your landscaping backdrop.

Charcoal Allan block retaining wall

#2 Cheating the excavation area – Limiting the MASS of your wall

Our 2nd problem on this list is Hardscape Retaining Walls require a tremendous amount of excavation and in most cases soil disposal.

Geogrid is used to combine the weight of the blocks, gravel and soil behind the wall.

The weight load could be as simple as soil, a parking spot, or a road. Each scenario requires a different amount of load bearing capacity.

In general, 60% of the wall height is used to determine how far back needs to be excavated to install the Geogrid.

#3 Unsuitable backfill material – Not enough gravel behind my wall

Problem number 3 is not having enough gravel behind your retaining wall, as the majority of the soil that is hauled offsite needs to be replaced with Gravel.

If 2 loads of soil are hauled out, and 2 loads of gravel are hauled in, this quadruples the backfill material costs when compared to not removing soil at all which is by far the most common INCORRECT method. This is why so many walls have been built by cheating the excavation zone, and using UNSUITABLE BACKFILL MATERIAL.

When your comparing proposals this will be very apparent in the pricing.

We tend to take retaining walls for granted, and expect them to stand forever because they are made out of concrete.

Concrete is a great building product, but if we expect them to last, we need to do what we can to ensure they don’t fail. ALMOST EVERY retaining wall you see failing is due to lack of gravel.

#4 No drainage system – Does my retaining wall need a drain?

We all know how much water can affect the weight of something. Multiply that over the length of your wall, for several feet behind your wall, for its entire life, and it's no wonder why you should want a drainage system behind your wall.

The problems most failed retaining walls see are either no drains have been installed, pipes are not protected from migration of fine materials (think clay soil plugging up the pipe), or the drains don’t drain to a good location.

Having water pool in your yard somewhere will cause you long term problems. By redirecting the water away from your wall, and getting it off your property , or at least to an acceptable designed area, you will prevent your wall from failing.

Remember water freezes in the wintertime, and will cause movement in your wall if it’s not drained away!

#5 Quality of work – How hard is it to build a retaining wall?

It takes the right training, and tools to build a retaining wall that will last! To build a structural retaining wall takes considerable effort, and skill.

To do a professional job takes the proper hand tools, gas powered concrete saw, laser level for perfect accuracy, string lines for straight and true walls, and the combined construction experience to put all this together and to address potential issues before they become a problem.

There is also a fitness requirement, ability to handle stress, and working in the elements. As well as a skill to run heavy equipment: Excavators, skid steers, dump trucks etc.

Allan Block provides courses on how to build a retaining wall properly, and we would highly recommend anyone wanting to build a retaining wall themselves to take a course, before undertaking a huge project like a retaining wall build.

#6 Upkeep – What are maintenance requirements of a retaining wall?

You love the look of your wall, and it is the focal point of your yard, but what about maintaining your wall?

Allan Block walls have relatively little yearly maintenance, however as with any excavated area, some settling is likely to take place over the first year or two. The settling will be minor if everything is properly compacted when the area is backfilled.

If there is any unusual or excessive settling, these areas should be corrected. Low areas will allow water to pool, and could make the problem worse over time.

Another thing to keep in mind is that any grade issues should be corrected,  ensuring you get a lifetime of performance from your Allan Block wall.

It is a good idea to finish your landscaping once your retaining wall is complete. Vegetation, whether that’s grass, or plants is a great way to control erosion, direct water where you want it, and generally sturdy up the soil surrounding your wall. Weeds or vegetation growing in your wall are possibilities, but if caught early, are easy to pull before they establish. Spraying them with a roundup or selective herbicide just like your lawn will be effective if done annually if needed.

#7 DIY – Should I build my own retaining wall?

Retaining walls are a large investment when built to Allan Blocks specifications, and are at least double the cost when they are not.

Yes, you read that correctly. If a retaining wall is built incorrectly and fails, not only will you need to pay for the cost of the original wall, you will need to pay to have it replaced. It makes much more sense to do it right the first time. In our opinion, a retaining wall build is better done by someone who has the training, skills, and machinery to do the job right.

If a homeowner really wants to build a retaining wall themselves, some steps need to be taken so that they can avoid their wall causing catastrophic damage to their property. As mentioned previously, Allan Block has a course on how to build retaining walls, and you can get certified right through the course. This takes time and money, and might be better if done by an expert.

Failed DIY retaining wall

Diy failed retaining wall abbotsford

If you think about it you really only get the advantages of a concrete retaining wall if it’s built well:

  • Lifetime durability
  • Increased amount of flat usable land
  • Focal point in any landscaping backdrop
  • Higher resale value if your Realtor & Home Inspector are in the know
  • And of course peace of mind

Allan Block retaining wall projects can drastically change the look and feel of your property if done correctly, and you will never regret investing in a wall that lasts, and looks great!

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Abbotsford, BC
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