This post is sponsored by Sakrete. In part one of our How to Build a Concrete Block Wall Project we covered the less glamorous side of masonry – the prep work. From demolition, to site preparation, and ultimately, A LOT of digging. Now that you’re up to speed on the initial phases of your project and you have a nice, solid, level footing in place, you’re ready for phase two! In this article, we’re going to walk you through the remaining steps of how to build a concrete block wall (or what to be aware of when you’re hiring someone to do it), touching on materials & tools needed, how the concrete block is laid, building code considerations, incorporating rebar, handling elevation changes, concrete grout for a rock-solid wall, waterproofing, drainage, whether to add a wall cap, and finally, finishing your concrete block wall. Phew! Whether you’re considering building a concrete block wall yourself, or you plan to contract out, this article covers many of the key aspects to making sure your wall project is a success!
Type of Mortar
Although there are certain walls, and even some specialized concrete blocks that are laid dry (without mortar), most typical concrete block walls are laid with mortar between the blocks. Ours was no exception. However not all mortar is created equal. And even within the same brand of mortar, you will find different types of mortar for different applications. For our project Sakrete sent us Sakrete® Type-S Mortar Mix, which is engineered for both above and below grade usage. Its specifications include, “High Strength (>1,800 psi), meets property requirements of ASTM C1714 and ASTM C270, ideal for projects requiring structural strength for brick and block foundations, applications from 1/4” to 1/2” and can be color pigmented with the Sakrete Cement Colors.”
Sakrete® Type-S Mortar Mix Uses
- Laying brick or block
- Scratch and brown coat in stucco applications
- Above and below grade applications
- Masonry parge or finish coating
- Interior or exterior
- Brick and block tuck pointing
In our case, the intrepid team from LM Stoneworks was using the mortar for laying the concrete blocks of our wall, and to install wall caps (more on that later). Despite this content being sponsored by Sakrete, my assumption was that the masons working on the job would not be able to tell the difference between the mortar they normally use (another brand), and the Sakrete® Type-S Mortar Mix supplied to us for this job. I asked the team of masons if the Sakrete mortar behaved any differently and the only feedback they gave was that the mortar did a better job of sticking to their trowels and to the concrete block. Score one unexpected win for the sponsor!
One important calculation is figuring out how many bags of mortar you will need for your project. Sakrete has a handy online mortar calculator on their concrete calculator page (click the “Mortar Mix” option on the left, and then enter the number of blocks you will be using). In our case, our Mason estimated roughly 500 blocks which equated to just under sixty 60 pound bags of Sakrete mortar. That’s a lot of mortar to sling!
Mixing to the Right Consistency
Mixing mortar may seem intimidating to the non-pro, but once you do it you will realize it’s not rocket science. Sakrete advises putting the dry mix in a wheelbarrow or mortar pan and adding water via a depression in the mix. Our crew’s approach was a little more seat-of-the-pants. Although a mortar hoe is recommended (this a short-handled hoe with a couple holes in it that help more evenly mix the mortar), the guys working on our project did it all via shovel.
The LM Stoneworks crew like the mortar at a consistency that when you scoop a small layer onto your trowel it won’t be runny or slide off when you turn the trowel sideways. It’s a Goldilocks scenario – not too dry and not too wet. Chuck and his team would regularly backbutter one side of the concrete block edges before installing the block. When doing this, the mortar should stick to the side of the block as the block is positioned into place.
Essential Masonry Tools for the Job
Thankfully laying block for a wall doesn’t require a vast arsenal of tools.
- Mortar Hoe
- Mortar Board Stand
- Block / Brick Trowel
Our mason favors a 12″ Brick Trowel for laying block. He has a much shorter brick trowel when laying brick. The margin trowel can be handy for working in tight spaces and scooping away concrete or mortar that is tucked in a corner.
- Margin Trowel
- Grinder with Masonry Blade
- Line Stretcher
- Line Blocks
- Mason’s Line
Laying the First Block
This is where the fun begins and the wall starts to take shape. Our project has some elevation change, so the first block was laid in the lowest corner. As you might imagine, starting on the high side of the wall would present some challenges since eventually your wall would need to defy gravity. Start at the low point if there is one and work your way up. The first block is pretty critical and you’ll want to make sure it, and all its friends, are installed level. Once you’re at this point, serious visual progress kicks in!
Applying the Mortar as the Blocks are Laid
Chuck and his crew made applying mortar to the blocks look easy. They usually had one of the crew mixing mortar and replenishing the supply on the mortar board. From there, one mason was loading the two end edges of each block and staging them. The mason at the wall had already laid a generous bead of mortar running on the top edges of the block that’s already in place. He would then grab a block from the staged blocks and tap it into place.
Filling in the Middle
As the corners of your wall begin to build up, you’ll start to work your way inward, ideally meeting in the middle of your wall. Chuck and his team made regular use of a Mason’s Line strung between the outer blocks via a line block and line stretcher. The line provides a visual reference for maintaining a consistent and level course of blocks.
Don’t Forget the Rebar!
Remember all that rebar we talked about in the first article on this project? There’s more rebar fun in building a rock-solid concrete block wall beyond the vertical bars coming up from the footing. The LM Stoneworks crew continued to lay rebar per the code requirements in our area – horizontally on every other course. Once the cavities of your wall are filled with concrete (“grout”), all that horizontal and vertical rebar makes for one robust structure.
Ideally, you or your contractor will have a discussion on the type of blocks to order when you’re getting prepped. In our case, the supplier forgot to mix in blocks with notches cut out for the rebar. Rather than dealing with returning and re-ordering, the crew notched them out on the jobsite and progress continued unthwarted by the mixup.
Handling Those Mortar Lines
How the mortar between blocks is tooled (if at all) depends on how you plan to finish the wall. For this wall, the block was going to be covered by stucco, so not much attention was paid to the lines beyond a quick scrape of the mason’s trowel to trim of the excess mortar. For a block wall that will have exposed blocks, the mortar is tooled smooth either with the rounded, handle-end of the trowel or with a specialized tool. The excess mortar on the faces of the blocks would be sponged off as well. Chuck said the stucco guys actually prefer the wall is not sponged off, which helps the surface stay more rough and creates a better bond with the initial stucco (brown) coat.
Sloped vs Steps for Elevation Change
One tricky aspect of our concrete block wall build was the amount of elevation change. We had mild elevation change on one side and pretty dramatic elevation change on the other side. For the portion of the wall that tied into an existing wall, we elected to do a step down. This step is created simply by omitting one course of block over that distance.
On the other side of the wall, we had a return leg going into the house and then a sloped portion that would eventually meet up with the level part of the main face of the wall. We contemplated doing steps there, but there would have been several steps and it would not have looked very graceful. Instead, we opted to create a gentle slope that would parallel the general contour of the existing terrain. This of course made the work on that part of the wall more complex.
Thanks to the radius of the wall, snapping a chalk line to determine the slope isn’t feasible. Instead, the LM Stoneworks crew built block higher than the expected cutline. Pro tip: using a length of PVC pipe held along the radius of the wall helps to define a smooth slope. Chuck then ran a pencil along the pipe to mark where the Husqvarna concrete saw was going to do its thing.
Plan Ahead for Lighting and Irrigation
If your wall stands between stuff you want to water or illuminate and the source of that H2O or low voltage electricity, plan ahead by creating a chase for those. Our crew managed this by cutting a square access through the base of one section of the wall and running a four inch pipe through it. Document the location of the chase if you’re not running sprinkler or low voltage lines through it right away so you can get to it later if needed.
Concrete Block Wall Grout
Some concrete block walls are built without rebar and without grout (grout is the concrete you pour into the cells of the concrete block after the wall is built). Without grout, you’re relying on gravity and your mortar to keep the wall intact. Even with a reputable mortar like Sakrete, this is NOT a good plan for most walls. The rebar you carefully installed throughout the wall will be useless without the concrete grout surrounding it.
Just when you thought you saw your last concrete truck, it’s time to call in another load. In case you need a refresher, 27 cubic feet is 1 yard of concrete. Believe it or not, our “little” wall project needed another eight yards of concrete to fill all those cavities! For a budgeting reference, concrete in San Diego runs about $130-$150 per yard, plus around another $350 for a pumper (not needed if your project is close enough for the truck’s chute to hit it).
PSI Isn’t Just for Pressure Washers
According to our mason, code here in San Diego requires at least 2500 psi for the concrete grout. Chuck likes 3000 PSI because it is a little richer and less likely to clog up in the pumper’s hoses. Trying to hammer jammed concrete out of the hoses is something you apparently want to avoid.
Double Check Before You Start Pumping
When the concrete truck showed up, the first thing the pumper did was climb up the ladder and visually inspect the concrete in the truck. It’s worth noting, this was concrete from a local supplier, NOT a Sakrete product. What he saw concerned him. The mix looked (and sounded) nothing like what the mason ordered. Instead of a nice, rich, smooth mix, this batch was filled with large aggregate likely to clog the hoses in a heartbeat. Without throwing the concrete company completely under the bus it appeared that they “accidentally” sent us a load that was supposed to go somewhere else, but then was returned. It made for a long day and a lot of phone calls, but that chunky batch of concrete was rejected, and was eventually replaced by a concrete truck filled with the proper 3000 PSI mix. You can’t just vacuum the wrong concrete out, so it’s worth making sure you are pouring or pumping the right mix.
Start Feeling Those Good Vibrations
Always an easy target for jokes at the World of Concrete show in Las Vegas, concrete vibrators are a key part of of this process. Once the cavities of your concrete block wall are filled with concrete, it is important to make sure the concrete is evenly filled into those nooks and crannies, and around all that rebar. Having bubbles in your wall is not a good thing. The crew here dropped the lengthy business end of a concrete vibrator into the grout and shimmied any stubborn voids away.
Concrete Block Wall Waterproofing
When it comes to concrete block retaining walls (and homes in general), water is enemy number one. Water building up on a wall underground can definitely cause problems over time and the last thing you want is all the hard work failing because you skipped a step or two. Our crew used a waterproofing material rated for below grade to line the entire portion of the wall that would be below the ground.
This is thick, messy stuff, that goes on like you’re rolling tar. Probably because it basically IS tar. If you’re applying below grade waterproofing yourself, wear your worst clothes and footwear for this one, or maybe some disposable coveralls. And don’t sit down in your car or truck until you know you’re not coated in the stuff (some tips from the crew here that might have made that mistake at one point in their careers). Follow your local code and manufacturer’s recommendation for applying the waterproofing.
Once the waterproofing is on, don’t make the mistake of backfilling right away. Some gravel will be going in the base of your retaining wall soon (more on that below). Between the sharp gravel and abrasive soil from backfilling, if you don’t protect your waterproofing, it won’t be so waterproof. For that reason, our crew applied a protective board to the entire section of wall that will be below grade. This board keeps gravel, rocks and anything else sharp you might have lurking in your backfill from scraping and puncturing your waterproofing.
Concrete Block Wall Drainage
If you look at some retaining walls in your neighborhood, chances are you’ll find quite a few that are failing. Sometimes that’s from an improper footing, inadequate reinforcement within the wall, soil movement, or (worst of all), NOT reading Home Fixated. In many cases the root cause is improper or non-existent drainage from the wall. As a result, water builds up behind the wall and can exert tremendous pressure on it. It turns out water is heavy!
On the somewhat sloped lot here, a significant amount of rain can accumulate inside our newly walled-off area. Granted we don’t get much rain here in San Diego, but it doesn’t take much to start causing problems. You’ll see a variety of approaches to drainage ranging from omitting the mortar between every other block on the bottom course, to pipe drains spaced regularly, to perforated drain pipe which is what was used on our project.
Step one for the drainage was to put a small layer or gravel around the base of the retaining portion of the wall – the below grade portion. A perforated drainage pipe (sleeved with mesh to keep out debris) is then laid at the bottom of the footing and backfilled with gravel. Although you will find heated disagreement on whether the the holes should be oriented downward or upward, it’s our position the holes should be aimed down, allowing the pipe to more quickly fill with water and begin draining. Most perforated pipe has two rows of holes, so you want those situated at roughly 5:00 and 7:00 rather than 11:00 and 1:00.
In our case we were also concerned about surface drainage so we could try to catch most of the water at the top before it percolates down to the perforated drain line. A series of vertical pipes tying into a 4″ drain that exits from the wall will eventually divert surface water before it has a chance to really build up. We left the 4″ pipes long so we can cut them down to the appropriate height once grade and landscaping get finalized. We also plan to add several more surface drains on another leg of the wall and what used to be the previous backyard.
Creeping Elegance – Adding a Wall Cap
A mentor of mine would use “creeping elegance” to describe the tendency to upgrade materials or features in a home improvement project. This creeping elegance is very sneaky, and will bust budgets quickly if you’re not careful. Originally, my intent was simply to slightly round over the top of the new concrete block wall. That gives the wall a bit more finished look and helps to shed water better than a flat surface. I considered doing a wall cap, but not very seriously until a neighbor suggested it. That sent me on a deep-dive into the far reaches of the google term “wall cap.” Two portions of our walls had different block widths, making a suitable wall cap all the more challenging to find.
Ultimately, I settled on some beautiful terracotta wall caps from Pacific Clay. I lucked out in that these particular wall caps come sized to fit both 6″ and 8″ wide concrete block walls. This bit of creeping elegance provided a second opportunity to put the Sakrete mortar to work. Pro Tip: our mason Chuck would mark his cut line in pencil and then spray a little clear lacquer to preserve the cut line as he ran the caps through the (wet) tile saw.
The Capella wall caps from Pacific Clay didn’t come with end pieces. As a result, the install was even more labor intensive because Chuck had to cut a triangle out of a sacrificial tile, and then fill that in to a triangle he cut out of the actual tile to be installed.
Despite the budget-busting qualities of adding this wall cap, it made a huge and positive impact on the look of both our house and the wall. In fact, I added it to two sections of existing walls to help tie it all together. Long story short, a nice wall cap should protect the top of your fancy new wall from the elements, and add a beautiful finishing touch in the process. Creeping elegance be damned – if you think a wall cap will enhance your project, go for it!
The Finishing Touch – How to Stucco a Concrete Block Wall
Our stucco contractor Dennis Stovel of Stovel Plastering advised us to wait at least a week before applying stucco so that the concrete on and in the wall can more fully cure. He also recommended we install the wall cap prior to his work, which we did as well. Thanks to some color-matching delays, we waited several weeks for the concrete to cure, rather than just a week or so. Our goal was to match the existing stucco on our home. . . what we failed to realize was how much color variation there was between an newer and older portion of the house.
Stovel Plastering grabbed a chunk of failing stucco from one wall (not hard to find!), and when we got the color sample back we realized it matched that wall perfectly, but was way too dark for the rest of the home. So we grabbed a chunk of stucco from the older, more sun-bleached portion of our house, and a week or so later we had a nice match for it. The color matching system they used not only was very accurate, but the 1’x1′ sample we got back (with our same heavy texture) made evaluating the color against existing walls a breeze. We solved our color differences by ordering a small amount of the darker color for a minimal amount of patchwork the darker area needed, and a larger amount of the lighter color to use for the color coat of the new concrete block wall.
Dennis and his crew mixed up the brown coat and spread that onto the concrete block wall. The first pass is pretty rough, but they then use a plaster darby to smooth out the coat and make it more uniform. After the brown coat cured, the color coat or finish coat was applied. This coat was applied in a thin layer that was then tooled with a float by a second crew member to give the color coat a rougher texture.
From there, the color coat is loaded into a hopper which then shoots the more heavy sand finish onto the wall. The Stovel team did a great job of matching both the texture and color to the existing home and existing wall. If you’re stopping short of the heavy sand finish, then the spray gun may not be needed at all.
Now You Go Build One!
Thanks to our sponsor Sakrete for helping making the project possible. We hope you enjoyed walking through how to build a concrete block wall, and that you’ll feel empowered to pursue your own concrete block wall project. Sakrete has great resources, tutorials, tips and videos available for both DIY’ers and pro’s alike on their website. If you have a wall project you’re proud of, or if you decide to tackle one of your own, please let us know about it the comments below. Happy mortaring and wall-building!