How to Build a Concrete Block Wall, Part 1

This post is sponsored by Sakrete. Have you ever had a seemingly small repair lead to a GIANT home improvement project? We have. Many times. In this case, it all started when some bees took up residence in our stucco landscape wall and then we had a bee rescue team remove them. Once I realized we were going to have a giant hole sawed into our stuccco landscape wall, I thought it would be a good time to demo the old wall entirely. And, once demolished, we could install a new wall further into the slope to create more yard space. The next thing you know, we were teaming up with Sakrete and a local mason and building a concrete block wall that would vastly change both the look and utility of our yard and our home. We’ll walk you through the process of how to build a concrete block wall (or what to consider if you’re hiring someone to build one for you).

Bushes, Fencing or Concrete Block Wall?

Usually, if you’re looking to define a landscape or create privacy, there is some debate over whether to plant hedges, install a fence, or a build a concrete block wall. Hedges can make excellent barriers, but in our case they also would have obstructed views. They also don’t provide much security.

Fences are an easy/inexpensive option, but aesthetically don’t work for every situation. Also, the lifespan of many fences is limited, particularly fences made of wood. A concrete block wall can last many decades or even centuries when built correctly. In our case, we also needed this new landscaping feature to serve as a small concrete block retaining wall below, and a freestanding wall above ground level. Since one side of the property already had a concrete block wall in place, and because we wanted the security and a partial retaining wall, the best fit in our case was to go with a concrete block wall.

Call Before You Dig

If you decide to build a concrete block wall, there is going to be digging involved – LOTS of digging. Whether the wall is a retaining wall or freestanding. Here are a couple scenarios you want to avoid:

1) Rupturing a Water Line.
Recreating a non-stop version of the Old Faithful geyser in your yard might make for a nifty tourist attraction, but you probably don’t want the water and plumbing bills that accompany that.
2) Rupturing a Sewer Line.
I don’t think we have to explain this one.
3) Rupturing a Gas Line.
Aside from being costly and disruptive, rupturing a gas line has the added impact of endangering your property, neighbors and anyone working in the vicinity.
4) Hitting Electrical Utilities.
Like messing with gas leaks, metal digging implements combined with high voltage can not only shut off your fridge, but also present an electrocution hazard.
5) Severing Cable / Phone Lines.
Are you still clinging to a landline? If so, you may be unflipping your flip phone to call your phone company with some explaining to do. Still using cable? When they say “cut the cord”, they usually don’t mean literally.

In California, we have Digalert and 811 services that will mark underground utilities in the area(s) you intend to dig. Simply indicate/mark your dig area boundaries, call at least a few days before you plan to start, and the various utilities in your area will circle back with you on potential hazards. You or your crew can then avoid those areas altogether or dig extremely cautiously around them if needed. Areas outside California have similar services. If you are unsure, contact your local utility company and ask what your options are for marking underground utilities.

To Survey or Not Survey

Before you break ground, you’ll want to be sure you’re breaking YOUR ground and not your neighbor’s or the city’s ground. Through careful measurements from plat maps and already-set property boundary pins, we were able to determine property lines clearly. If your concrete block wall is potentially on land other than your own, you may want to invest in having a survey done to definitively mark your property lines. Surveys are not cheap (in Southern California, they often run $1000+). Despite the cost, they are sometimes well worth the investment to avoid potential issues with neighbors, your local municipalities, or title/encroachment issues when you or your neighbor decides to sell.

Demolition

If you’re building a concrete block wall where there are no existing walls, fences or ridiculously-rooty vegetation, you’re in luck! Crack open your favorite beverage of choice and laugh with Schadenfreude as you read about our demolition process. In our case, demolition involved taking out our formerly bee-infested stucco wall, but also removing what ultimately was thousands of pounds of Bird of Paradise plants and root systems. Unspeakably evil root systems.

Demolishing the wall wasn’t so bad. The builders of the wall had thoughtfully built the wood framing in direct contact with the soil,s and termites had already taken care of weakening the overall structure. With a little extra persuasion from our Bosch SDS-Max Hammer, strategic sledgehammer blows, and dramatic, martial-arts-inspired demolition techniques, the wall came down pretty quickly and easily. We also had a small, low concrete block wall to remove. That presented more of a challenge thanks to the concrete footing that needed to be extracted.

Lastly, five giant Bird of Paradise plants that had likely been there for decades needed to be cleared. I hilariously thought I could fit ALL the debris in a Bagster or two. Five+ Bagsters and one separate dump run later, I finally extracted the plants and roots systems in and around our new wall.

Building a Concrete Block Wall – Follow the Code

Concrete block walls can last eons when they’re built well, or they can turn into leaning, multi-ton disasters when built incorrectly. For this reason, and others, it is wise to follow your local building codes and requirements. Doing so can not only help you avoid the ire of your local code enforcement officer, but it also usually means you’re following best practices for a safe and strong wall. If you’re tackling the project yourself, your local planning department often has resources you can use to plan your project. If your wall is high enough or is a concrete block retaining wall, you may also need to pull a permit as well.

We had the benefit of many years of a professional mason’s experience thanks to Chuck Locket of LM Stoneworks handling our concrete block wall build. Even so, the city’s documentation was still is an excellent resource. Here in San Diego, the city puts out several specifications for projects like fences, masonry and concrete block walls. For example, if you are building a “masonry fence” (a freestanding concrete block wall that is not retaining soil), their guide to Wood and Masonry Fences is a good document to review. San Diego’s code (as well as your own local code) likely covers important considerations for how to build a concrete block wall, including (but not limited to):

• Masonry Blocks
  Typically 6″ or 8″ which refers to the width of the blocks.
• Concrete
  Code will dictate the PSI (strength) of the concrete, along with dimensions for footings and grout
• Mortar
  In our case, Sakrete® Type-S Mortar Mix. Code will specify joint size and minimum PSI too, often referencing an ASTM standard.
• Grout
  This is the concrete that gets poured into the concrete block wall. Again, it must meet minimum PSI requirements.
• Reinforcing Steel
  aka “Rebar” – Code will specify not only the size (diameter), but also the overlap of bars, and where they are placed within the footing and wall.
• Mortar Key
  Used in some walls to create a bond between the footing and first course of block

Life will be easier for you if you’re building a freestanding wall vs a concrete block retaining wall. If your wall will be retaining any soil, then the code and requirements for a safe and solid concrete block retaining wall will vary. Aside from the items above, the code will likely discuss proper drainage, soil considerations, backfill, etc. For an example of requirements here in San Diego, check out the City of San Diego Development Services Retaining Wall Sloping Backfill and Retaining Wall Level Backfill bulletins. Again, please keep in mind, these are information bulletins for the City of San Diego at this point in time, but you should be basing your project based off of code requirements and best practices in your specific area.

Marking the Wall Location

Once we made sure we were safely inside our property line, the actual location of the wall was marked off at its corners, as well as along the radius of the curved portion of the wall. Because the wall was running parallel to two of the home’s exterior walls, the crew carefully measured out from the walls to make sure the straight portion of the wall was square with the home. As with just about anything curved in construction, expect to have a more expensive, complicated and time-consuming project if you are incorporating curves into your concrete block wall.

When determining the radius portion of the wall, a garden hose was a convenient tool for playing with different curves before marking a line on the ground to mark the final location of the curved wall. I wanted to follow the curve of a nearby corner of the lot to help the curve blend in well with its surroundings and help soften the overall look of the wall.

Digging Out the Footings

Often the most grueling and frequently short-cutted aspect of the build, digging out the footings is an absolutely critical step in how to build a concrete wall correctly. Consult with your local code for the depth and width of your footing. The footing is much like the foundation of your house – without a solid one it doesn’t matter how well built the rest of the structure is. Getting a nice, solid footing is absolutely key to the strength and longevity of the wall. Having a level footing also makes building the rest of your wall easier.

The type of soil you are digging can have a direct impact on how many expletives are vocalized during the excavation of your footings. If you have sandy, easy to dig soil, consider yourself very lucky. If you have rock-hard, clay soil, consider yourself not nearly as lucky. I also suggest contracting out for this portion of the job if you are not already. Regardless of the type of soil, using a demo or breaker hammer equipped with a clay spade bit makes the dig a lot more manageable. Most likely you’ll be using something with a 1-1/8″ hex shank bit, or an SDS-Max device. While I used a Bosch SDS-Max tool for the demolition, Makita was the popular choice for the footing excavation on this project.

How wide and how deep you’ll be digging for the footing will depend on your local code, which might also factor in considerations such as type of soil and frost line considerations. Here in San Diego, we worry more about earthquakes than frost.

Relocating / Capping Irrigation and Sprinklers

Since you carefully read our advice to “call before you dig” hopefully you will avoid digging through anything you’re not supposed to. One thing the utilities won’t mark for you is your sprinkler lines. One of our first steps was to mark individual sprinkler heads. That first step often gives you a clue on where you might run into sprinkler lines. We managed to locate a couple of the lines early in the digging process to be removed, capped and re-routed where needed. We also managed to completely sever one sprinkler line, which didn’t become apparent until after our automatic sprinkler kicked on and partially flooded our beautiful new footing hole. PRO TIP – Turn off any automatic sprinklers before and during your entire wall build project (except for brief manual tests)!

Forming For Your Footing

After what seemed like several dozen cubic yards of dirt were extracted from the line designating the outer boundary of our wall, it was time to form the footings. Much of the “form” is simply created by the area being excavated, so it pays to have a neat and tidy hole for your footing. That hole should also match the code requirements for the overall size and shape of the footing.

In our case, a portion of the wall was not only in a radius, but it also had a substantial elevation change. Since the concrete block wall was going to be built plumb and level, the footing needed to be level as well. If you start off with a footing out of level, correcting that when you start stacking and mortaring blocks can be an unnecessary pain. By creating multiple heights for each section of sloped footing and then forming a sturdy dam at the end of each level, our mason Chuck was able to keep all the sections of footing level and still adapt to the elevation change on the left, sloped side of the wall.

Chuck and his crew defined the top of the footing with a 2×4 which was carefully checked for appropriate height and for being level. It was then nailed in position with steel forming stakes and duplex nails. The bottom of the 2×4 represents the top of the footing pour. The 2×4 in this case is there to make the pour efficient. When the concrete is being pumped the crew isn’t having to reference a transit level and the depth of the concrete throughout the pour. The 2×4 also provides support for the initial rebar. Numerous kerfs were cut into the 2×4 so they could bend it along the curved portion of the footing.

Prepping Rebar – Rebar Placement & Number of Bars in the Footing

Rebar doesn’t do nearly as much good if the sections of bar butt up against each other. That’s why overlapping the ends of rebar is critical. As always, check your local codes, but per our mason, 40x the rebar diameter is a common rule of thumb for overlap. So if your steel is 1/2″, then (1/2 x 40) equals 20″ of overlap. See, your math teacher told you this stuff would come in handy at some point!

Code will also have something to say about how much rebar is used. For this project, three bars were run lengthwise in the bottom of the footing. The footing also needs to tie in to the wall itself. Since the wall isn’t built yet, this is done with L-shaped rebar that will go from the footing up into the lower part of the wall. The interval varies per code but in ours they start the verticals about 4” in from corner and then 2’ on center to avoid the edges of blocks. The trick with vertical placement is to avoid having a vertical come up where an edge of a block will be. Those vertical lengths of rebar can be “persuaded” a bit if they run into obstacles when stacking the blocks, but with some careful measuring much of that can be avoided.

Once the horizontal and vertical rebar was in place and the form was finalized, the LM Stoneworks crew even vacuumed loose soil and debris from the trench prior to pouring the footing. If there is a lot of loose soil settling can occur. PRO TIP: a nice, tidy trench tends to give a favorable first impression to most inspectors too!

Calculating the Quantity of Concrete for the Footing

Figuring out how much concrete you’ll need for your footing is vital, whether you’re trying to figure out how many bags of concrete you’ll need to mix by hand, or especially if you’re ordering concrete delivered by truck. In the case of this wall, it was definitely more concrete than anyone would want to mix by hand. Googling “concrete calculator” will give you many different options for calculating what you need, however if you prefer to flashback to grade-school math, the main stat you’ll need to know is 27 cubic ft equals one yard of concrete.

Since we were ordering the concrete by truck, calculations are all the more critical. Generally, you want to order a bit more than you calculate so that you avoid the financial pain and humiliation of running out of concrete part way into your pour. However, the flip side to that is that the overage from the concrete in our case is pumped back into the truck. They then take the concrete back to the yard for it to be recycled in some fashion. Although the overage doesn’t truly go to waste, you’re still paying for it. Speaking of paying, it’s worth touching on costs for the concrete, which can vary quite a bit depending on where you are.

In San Diego, if you’re having a truck deliver it ready to go, concrete will set you back about $130-$150 per yard. If your pour location is further than the concrete chute can reach, you will also need to hire a concrete pumper. Here in San Diego, that costs about $350 (more if the pumper is pumping really long distances). For this wall, we needed about 7-8 yards of concrete for the footing and a pumper to get it from the truck to the pour.

Pouring the Footing

Preparation is key, and hopefully you or your contractor will have taken steps to prep the form as we discussed above. You’ll want to make sure the form is solid, the rebar is secured and in the appropriate place, and all that’s left is for the concrete to be poured. Concrete is HEAVY, so avoiding blowouts is important! In our case, the pour is also time sensitive as the concrete companies only give you a certain window of time to pump. Once you exceed your allotted minutes, then you start getting billed by the minute!

For this wall, the pour went smoothly, and we quickly went from having a massive trench to having a much smaller trench with a massive concrete footing. Given that the footing looked like something that would support the Berlin wall, it was reassuring to know this wall wasn’t going to go anywhere once it is completed.

Now that we’ve done the planning, demolition, digging and footing, stay tuned as we dive into Part 2 of How to Build a Concrete Block Wall. We’ll take you through the process step by step as the blocks are mortared into place, more rebar is added, concrete grout is poured into the wall, the retaining portion is waterproofed, drains are added, a fancy cap is added to the top, and we finish the concrete block wall with stucco to match the house!

More Info - via Sakrete

This is a sponsored conversation written by me on behalf of Sakrete. The opinions and text are all mine.