Building an exterior block screen

Summary: Learn how to build an exterior block screen, build the piers and lay the screen blocks.

Constructing block screens involves the tools and techniques used in bricklaying, but are modified to suit the block size, shape and use. If building a screen higher than 600mm (2ft) it will need to be reinforced vertically with 16mm (5/8in) steel rods and galvanised-mesh strips horizontally. The screen will also need to be reinforced with piers no more than 3m (9ft 9in) apart.

Building the piers

  • Mark out the footings or foundation for the wall. This needs to be twice the width of the pilaster blocks (the blocks that make up the pier). The depth depends on the height of the wall and ground conditions, but generally a concrete base 375mm-450mm (1ft 3in-1ft 6in)) thick should be more than adequate for a block screen 2m (6ft 6in) high. The top of the footing should also be at least 150mm (6in) below ground level to protect it from frost.
  • Before the concrete sets embed the vertical pier-reinforcing rods into the footing. The rods should be supported using guy ropes until the concrete goes off.
  • Mix some mortar with which to bond the blocks together using water, one part masonry cement and five parts building sand.
  • Using a brick trowel scoop up some mortar and make a bed at the bottom of the first steel reinforcing rod. 
  • Lower a pilaster block over the rod, and set it into mortar laid around its base. Make sure the block is perfectly level and that the locating channel on the pier will face the opposite pier.
  • Fill the block with either mortar or concrete and proceed to lay another two pilaster blocks on top, so the height is equivalent to two screen blocks. Continue this same process with all the piers. The pilaster blocks used for building the intermediary piers (located between the ends of the wall) have channels on two opposite sides for the screen blocks to be fitted on either side of the pier.
  • When you have constructed all the piers let the mortar harden overnight.
Lay the second course of screen blocks between the first two piers ensuring the vertical joints line up perfectly.

Laying the screen blocks

  • The following day, lay a mortar bed for two screen blocks next to the first pier.
  • Spread the vertical edge of a screen block with mortar and push it into the pier’s channel and tap it into the mortar bed. Use a spirit level to check the block is level and tap it to make any adjustments.
  • Mortar the edge of the second block and place it alongside the first. When spreading mortar on the edge of screen blocks, take care not to get the mortar on its face. Chamfering edges of the mortar on the block neatly can prevent this.
  • Move to the next pier and lay another two blocks in the direction of the two you have already laid. Then run a bricklayer’s line along the top of the four screen blocks to indicate the top edge of the first course of blocks.
  • Continue to lay the screen blocks to complete the first course.
  • Lay the second course of screen blocks between the first two piers ensuring the vertical joints line up perfectly.
  • Lay the first two courses of screen blocks between all the other piers using the same method.
  • Before building any higher, the galvanised wire reinforcing mesh should be embedded in the mortar along the top of the screen.
  • Continue building up the screen by adding pilaster blocks to the piers and screen blocks to the wall until you reach the required height, which should not exceed a height of 2m (6ft 6in). The galvanised wire reinforcing mesh should be used on every other course.
Coping slabs should be laid on top of the piers and along the top of the screen.

Finishing

  • When you have reached the required height, coping slabs should be laid on top of the piers and along the top of the screen. Use the builder’s line to ensure the coping slabs are level.
  • Finally you need to point the joints. This not only gives the joints a neat and tidy appearance but also makes them watertight.



Tools needed

  • Brick trowel
  • Cement mixer
  • Shovel
  • Spirit level
  • Bricklayer’s line

Materials needed

  • Steel rods
  • Galvanized mesh strips
  • Pilaster blocks
  • Masonry cement
  • Building sand
  • Coping slabs

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