How To Build A Wall
The fourth instalment of our ‘How to’ series of guides, will teach you the basics of bricklaying and demonstrates how to build a wall. We have multiple How-To Guides to our YouTube channel so be sure to subscribe as there are more videos coming soon.
Foundations or footings as they are sometimes called, aren’t always necessary with a small wall that is less than 600mm high. If you have an existing concrete base or an area of firm and stable paving, you could build straight onto that. However, because our planter is going into an area of the garden, we’ll need to form a simple strip footing using concrete.
The size of the footing is determined by the walling blocks. You need to have around 100mm of working room or spread on each side. Because our blocks are 150mm wide, this means the footing will need to be 350mm or so in width. Our wall is only going to be 450mm high, so we don’t need a tremendously deep footing, between 100mm and 150mm will be plenty. We also need to start laying the walling blocks a little below ground level, say 50mm, so the footing won’t be visible when the wall is finished. So this means we need a trench 200mm deep and 350mm wide.
(Get rid of any weeds, topsoil or other organic matter)
Laying Foundations for the Wall
Prepare a mix, using six-parts aggregate to one part cement. Mix the sand and gravel first with just a little water, ensuring the cement is evenly distributed throughout, before adding extra water. You need a fairly wet, pourable concrete so that it flows into the trench footing and is easy to level out.
The concrete is simply poured into the trench, spread using a shovel and roughly levelled out before being tamped with a length of timber or a float trowel, to expel any air pockets that might have formed. This also creates a rough and rugged finish, that will be an ideal base for the mortar to bond to when you start building the wall. Ensure the concrete is flat, with no slope or fall in any direction. Leave the concrete overnight, to give it a chance harden.
Building the Wall
Start by dry laying the blocks to give you some indication of where they’ll sit on the footing, and if you look carefully, you’ll spot that we need to cut a block to get it to fit along the front edge (see video 2:24). Move the blocks out of the way for a moment while you set up a taut string line.
For any bricklaying task, you need a bricklaying mortar. This is made using three-to-one mix, that’s three-parts building sand to one-part cement, with a little plasticiser to make the mix more workable and just enough water to make a smooth and pliable mortar. Remember that wet mortar can burn exposed skin, so make sure you’re wearing suitable protective gloves and have long sleeves to protect your arms as well.
Laying the Blocks
First make the bed, which involves placing a line of mortar on the concrete footing and rippling it with the point of the trowel, to make sure there’s some give when we place the block onto it. Put out enough mortar for the block you’re about to lay, with a little bit extra to ensure the end of the block will be fully supported. We will need a mortar joint between the block and the existing brick wall. To achieve this, spread or as it’s known in the trade, “butter”, some mortar onto one end of the block so that when it’s pushed against the wall, a vertical mortar filled joint is created (see video 4:20).
Now the block is in position we just need to settle it down to the correct height as indicated by the string line. For this use a rubber mallet, tapping the block firmly on its top about 1/3 and then 2/3 along its length, to take it down to the correct level a bit at a time. Although the string line should be a good guide to level, double check using a spirit level, making sure the block is flat both along its length and across its width.
As you continue to lay the blocks, keep using the spirit level to check both the flatness across the top of the blocks and the alignment along the face of the blocks.
Where there are gaps of less than a full block, we need to cut a block to fit. There are two very different tools that are commonly used to for cutting blocks: a bolster chisel and a hammer or a power saw. It’s best to leave the power saw to the professionals, so we recommend a simple hammer and chisel. Whichever tool you used, ensure you have marked the block carefully before you cut.
Laying the Second Course
We’re ready for the second course now, and this is done in exactly the same way. Notice how we’ve staggered the blocks on this second course to ensure that the vertical joints don’t coincide (see video 5:22).
The wall is going to be finished with a coping, a flat stone that sits on top of the wall and gives it a neat and tidy finish. However, before you do that, it’s a good idea to point the horizontal and vertical joints, smoothing off the mortar that has been squeezed out when tapping down the blocks; as well as filling any gaps. Use a small pointing trowel and a pointing bar to do this.
As we did with the blocks when we started this project, dry lay the coping stones to see how well they fit, and whether any will need to be cut. There are two key things to check with coping stones. Plan the joints between the coping stones, as with the blocks you need to avoid having vertical joints coinciding, so they will need to be offset. Ensure there is an overhang both along the long face and at the short end, and allow a 10mm joint between each coping stone. It’s a good idea to cut any pieces you need before you start to lay.
In exactly the same way as we did with the walling blocks, the copings are laid on a bed of mortar, with one end buttered up before being placed into position. Once on the mortar bed, we use the rubber mallet to tap it down and then use a spirit level to check that it is flat along its length, but with just a touch of fall towards the front edge, so that any rain water will run off. All we need to do now is point them as we did with the walling blocks, making sure all of the joints are properly filled with mortar and smoothed off, for a tidy finish.