Building an exterior block screen
Summary: Step by step instructions on building a block screen to give privacy and divide up areas in your garden.
Using decorative concrete blocks to make a screen wall in your garden is an easy way to divide up areas or provide some dappled shade and a degree of privacy.
Materials
Depending on where you purchase your blocks (try your local builder’s merchant), there may be a range of patterns and even colours available. Most blocks are around 300mm (12”) square and 100mm (4”) deep.
The cast concrete blocks you will be using to build your screen don’t work in the same way as normal bricks or blocks. Because of their pierced decorative effect, they work much better if they are laid in line rather than staggered like a normal wall. This means that you need to create piers to strengthen the wall. Blocks called pilasters are sold to build the piers with – these specially-designed blocks are designed so that the screen blocks fit into a cast recess, forming a strong joint. Pilasters are available in end, intermediate and corner versions, and should be placed no further apart than every 3m (10ft).
You will need to reinforce your piers with 16mm steel rods. The pilaster blocks are designed so that the rod can be inserted down the centre of the pier. If your wall is going to be more than 600mm (2ft or two blocks) high, you also need to reinforce it horizontally by adding lengths of galvanized wire mesh between courses. Cut to size with wire cutters so it doesn't protrude over the edge of the blocks.
Caps and copings for the tops of the pilasters and wall should be purchased too – these will finish the top of the wall in an attractive way, and help to add strength.
Building sand and cement are needed to make your mortar – see our Mortar Mixes project for help with this. Because screen blocks are often white, you might want to use white cement and silver sand to produce a light coloured mortar to match. Or you could use a cement dye to make a contrasting darker mortar. Be careful not to let the mortar stain the blocks when building your screen.
Foundations
Like all walls, your screen will need a solid foundation to support it. See our projects on Building a Garden Wall and Foundations for help with this.
Make sure you drive the steel reinforcement rods into the ground before you tip the concrete into the foundation trench, and hold them in place with guy ropes until the concrete sets. Be sure to measure carefully, including 10mm between each block to allow for mortar joins, so that the rods are in the correct place to support your pilasters!
Building the Screen Wall
Set up a brick line to make sure your screen wall is straight. Start to build the piers first, filling the centre of the pilaster blocks with mortar to ensure the reinforcement rod is held securely in place. Do not build the piers any higher than three pilasters/two screen blocks to start with. Point the mortar joints, using an off-cut of garden hose to run along the joints to give a neat, concave effect. Let the piers set overnight before starting on the screen blocks.
Lay two blocks next to the first pier, then another two next the pier at the other end. You can then work towards the centre, filling in the gap. Repeat this for each section of wall, and add another layer so that your screen is two blocks high. At this point, put a layer of mortar along the whole wall and piers, and lay a length of reinforcing mesh along the wall – embedding it in the mortar. You can then add another two courses of block, again building piers first then fitting the screen blocks in.
You can build your wall up to 2m (6ft 6”) high, but don’t build more than four courses at once. Add a layer of reinforcing mesh every two courses, and allow the mortar to dry after four courses. Keep pointing up the joints as you finish each course.
When you have reached your desired height, mortar another length of mesh along the top and lay your caps and coping blocks.
All project content written and produced by Mike Edwards
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