SERIES QUICK LINKS
PART 1: PROJECT PLANNING
PART 2: FOUNDATION AND BASE STRUCTURE
PART 3: LAYING CONCRETE BLOCKS
PART 4: PAVERS
TENTATIVE SCHEDULE FOR FUTURE POSTS:
PART 5: WOOD BENCHES
PART 6: PREPARING ELECTRICAL AND PLUMBING
PART 7: COUNTERTOPS
PART 8: FIREPLACE FINISHING
PART 9: EQUIPMENT INSTALLATION
PART 10: PERGOLA
FOUNDATION AND BASE STRUCTURE
In Part 1 we covered the basics of coming up with the design, rough planning materials, and determining space. In Part 2 we covered how to prepare the ground for foundations, running any underground conduit needed, and pouring foundations. Now we’ll talk about how to lay the concrete block that forms your structure.
As a recap, for our outdoor living space we settled on an outdoor kitchen, gas fireplace, two sitting walls, and a pergola. The fireplace top serves as the 4th pergola post and sitting walls link the fireplace to the two adjacent posts. The three posts are then wrapped in decorative stone a little higher than each seat. See Part 1 for the rough drawing.
Calculating the materials you’ll need is the first step of this process. You’ll need concrete blocks, rebar, mortar, and concrete. The rebar goes inside some blocks then most of the blocks are filled with concrete, adding significant strength and rigidity to the structure. For ours we filled all blocks on the ground with concrete then were more judicious on any floating ones – those on some kind of raised platform – in order to evenly space the weight out and get the best possible weight to strength ratio, which we’ll talk about below.
There are a few choices in mortar. After doing a bit of research I decided to try a relatively new (at least to me) product on the market, 1-2-3 Mortar. This product is intended to make laying mortar beds similar to applying cake icing – simply mix in the bag, squeeze out of a tube, then lay the blocks.
As is the case with many products it wasn’t quite as simple as the video made it seem. I bought a few cases of this but ended up only using two boxes before giving up and moving to regular mortar. There were four main problems I ran into with this product:
- It was very hard to get the mix to squeeze out. Even after adding more water than the instructions called for I was finding it very hard to keep a steady stream of mortar flowing from the bag.
- Once the bag was nearing an empty state there was a ton of left over mortar that was very hard to get out. I ended up cutting open both bags I used and scraping out the excess, which covered about another block, per bag.
- The bags did not cover as many blocks as advertised, even when mixed exactly per the instructions.
- The consistency was not tacky enough to stick the sides of blocks – it was a speed/timing act to get the block down before mortar fell off the side.
If you are only doing a small area this product is absolutely fine. I’d shy away from it if you have 20,000 pounds of block to lay.
What we ended up using was regular Type S Mortar mix – high strength and intended for load bearing use.
As for concrete blocks, they come in a number of sizes and you can also find custom shapes out there, though you’ll pay a premium for them. The standard sizes are 8x8x16 (hollow), 4x8x16 (hollow), and 2x8x16 (solid). You can use other sizes but most of what you should need to do can be accomplished with these standard and readily available sizes.
Note that there are a few different shapes of the 8x8x16 blocks. If you really care about all the types you can read about them here.
- Stretcher blocks have protrusions, called stretchers, along the lengthwise walls, making them ideal for non-corner applications. These are smooth on the long faces but do not make for a smooth and nice looking short end face.
- Corner blocks are smooth and make for a good corner appearance. These are smooth on all outward facing sides.
- Sash blocks are just like corner blocks only they have a groove, called a sash groove, running down one of the short ends. This is intended for metal from a door, window, or other structural detail to slide into during the construction process.
Most big box stores will ship pallets of blocks to you for a small fee.
DRY STACKING BLOCKS
The next step is to lay out your blocks to ensure that your measurements and planning actually make sense. Nothing worse than getting to the end of a course only to find out your measurements were off and you have to adjust everything mid stream. During this step focus on getting the perimeter laid out how you want it, keeping in mind any conduit that you ran will need to run either to the inside or through a block.
Once you have the perimeter run you can start filling in the center, if that is what your design calls for. In our case the first course is also supplying the base for the fireplace. We chose to put a few cinderblocks in there then surround them with concrete mix, then top with a mortar mix.
Once you have blocks laid out roughly where you want them mark the ground using a chalk line, spray paint, chalk, or some other means so that you can follow the lines when laying the first course.
Now you can figure out the height you want and get a true estimation for how many blocks you need. This is simple math at this point – the first course times the number of rows high you want it. We were able to order all blocks ahead of time and be within 10 blocks when we were done – out of a 20,000 pound load.
Before you move on to the next steps measure, measure, measure! Make sure that anything that is supposed to fit inside your blocks will fit as expected. I’d also recommend making wood, cardboard, or foam templates that match the size of the gaps you will need. We’ll discuss my horror story and my lesson learned below…
THE FIRST COURSE
The first course of blocks is your base and it is extremely important that these be level and solid. Take your time to lay a solid mortar bed then place each block into it according to the layout you marked in the previous step. After the first block put a layer of mortar on one end of the next block. I found that I had to somewhat sculpt this by hand to keep it in place while I laid the block. Once laid, tap lightly with the end of your trowel to set them into place, both horizontally and vertically. Finally, place a level on top of the block and make sure that it is level in all directions. If it is not, lift up, add mortar as needed, then re-set. Do this for every block. For every block after the first it is good to also use your level or some other straight edge to ensure that the block faces are on the same plane.
As you start laying your course you will inevitably end up with pieces that just don’t fit right. Or perhaps your design calls for this from the outset. You can fairly easily break blocks with relatively clean lines using a hammer and a chisel. But if you have a need to expose any of the edges you are breaking you’ll want something cleaner. In our case we used a 4″ wet circular tile saw fitted with a diamond blade. Simple mark, cut, then tap gently with a rubber mallet and the block will split.
The remaining courses should be staggered in such a way that the joints are overlapping, as shown in the image below. This adds strength to the walls. It is still extremely important to make sure that each course you lay is level.
You’ll notice some gaps in the picture above – these were intentionally left in the kitchen area to allow for air flow, since we’ll have a natural gas hook up under the countertops.
The mortar process had a very small learning curve but you quickly get a rhythm down and can lay blocks pretty quickly. For me I used a small brick trowel. I just scooped up half a trowel’s worth of mortar, tapped it onto the top edge of the brick, then repeated until all top edges are covered in about the same height of mortar.
For the work done here we laid 3-4 courses high at a time then let them set. Once the courses were laid we inserted rebar into every 3rd or 4th opening then filled all blocks to the top with concrete. This adds a great amount of strength.
It is easy enough to test this strength out – join 4-5 blocks using just mortar then 4-5 with mortar and concrete, give a few days to set, then hit it with a sledge hammer. The concrete filled blocks are much, much stronger.
Continue building up your courses, following your design, until you get to the desired height. It is best to consider common seat, bar stool, and other heights if you are working on an outdoor living space. Make sure you take into consideration the thickness of whatever you are going to use as the top and facade for your blocks.
The final course depends a lot on your design, height, and what area of the project you are working on. In our case the final course was a mixture of open core blocks, horizontally laid 4x8x16’s, and horizontally laid 2x8x16’s. We will be covering the tops of all surfaces, except the very top of the chimney, with concrete “countertops” so it doesn’t really matter whether our final course is a open or closed core block.
Spanning gaps took a lot of research. Perhaps there is one but I’ve yet to find a really good article talking about how to safely span gaps in cinderblock projects. If you want to put a door or window into a cinderblock wall there is a ton of information out there. But if you want to do something more complex – say, create a fireplace opening, there isn’t a lot that I’ve been able to find.
So… Let’s go through what little bit I know…
Any span must be supported properly or they will be structurally unstable. DISCLAIMER: This post is by no means an expert article but simply meant to give you enough information to figure out what direction to go in then research or seek professional support for the path you choose.
From my research there are two primary ways of spanning a large gap:
lintels or flat irons
Lintels are basically large angle irons, specifically sized for holding the weight of different types of blocks and brick. Make sure you get the right size for what you are working on. The one linked above is for bricks but isn’t necessarily the right size to hold cinderblocks.
Using a lintel can be done a couple ways with cinderblocks. The first is to place them under the outside edges of the blocks and use them like rails with blocks laid inside to span the gap. The second is to use Lintel blocks (or, better, score and cut your own) so that you can lay the lintels with the backs of each “L” facing each other so that the upright portion of the lintel is inside the block.
For the openings in the kitchen area we had gaps where the cabinets were that we used lintels to span. In our particular case we had some odd sizing to deal with so we actually used concrete backerboard strips, topped with a lintel, with the blocks on top.
Laying a concrete slab
This section states, “just as you would do on the ground”, a lot. See Part 2 if you don’t know what to do here.
The second method is to lay a concrete slab. This is done much like you would do on the ground only you have to supply an artificial ground until the concrete cures. To do this simply measure and cut a piece of 3/4″ plywood then secure at the right height. In our case we secured the perimeter with 2×4 cleats then put a support 2×4 beam in the center.
Once you have this in place, put the forms around the outside, just as you would if this were on the ground. The only difference is that you’ll need to secure the outside of the form to the cinderblocks.
Once you have the forms in place pour the concrete, just as you would on the ground, only now you have to haul it up to whatever height you are pouring into. Fill half way, then place rebar in horizontally. Place this in a grid pattern, ensuring that the rebar overlaps the cinderblock that is supporting the load by at least a few inches. In our case we put rebar in with 3-4″ squares in the grid – probably more than we needed but we erred on the side of caution, especially since our fireplace will also be supporting 1/4 the load of the pergola.
Once cured the structure is quite strong. I’m not too far south of 250 pounds and it holds me just fine. Note that the apparent flexing in the concrete is just where I let the front edge of my board slacked too much during curing. I really needed another support. This thing is quite solid.
From here the rest of the fireplace structure is the same as working on the ground, only now the ground is our slab 6 feet in the air. Continue stacking courses as needed but strategically choose which ones to fill with concrete and rebar for stability. In our case we only filled blocks that were directly above the below walls so that we could limit the weight placed on the span itself.
For our third section of the chimney we only needed a few blocks so we just used a piece of concrete backer board to hold it in. We then interlaces the blocks then filled the ones over the wall below with rebar and concrete. We’ll also add a concrete “countertop” above the concrete backer board, which will add additional rigidity and strength. Note that we did not put concrete directly over the span of the backer board – that would have been far too much weight and would have resulted in bowing at the least, collapse at the worse.
DEALING WITH MISTAKES
So remember when I said, “measure, measure, measure”? Well, I said that because I learned the hard way.
I measured multiple times for the opening of the grill yet managed to measure wrong multiple times. As embarrassing as it is I also made a template out of wood and managed to size it incorrectly too. So I went to drop the grill into the newly finished block structure only to find that the structure was about an inch too narrow.
Ugh. So now what? Well, I got to find out how much stronger concrete filled blocks really are. I took a sledge hammer to about a quarter of the structure and, remeasured, then started re-laying block. Only this time I actually took the grill itself and make sure it fit during the dry lay phase of the new courses.
This isn’t fun – make sure you measure. In the picture directly above the left front section, front where the grill area is to the wall, all had to be ripped out. This how I know how much stronger concrete filled cinderblock is…
So that does it for concrete block. This is a relatively short article but this is the biggest part of most projects. Take your time and think before you lay the first stone and it will all come out great. Oh yeah, and measure.
The final step for us was to lay concrete backer board over the countertop so that it is ready for us to pour the countertops, though there are a few steps before that.
Next installment we’ll talk about laying pavers.