Summary: Learn how to build a partition wall with concrete blocks, insert control joints and cut concrete blocks.
Concrete block walls need the same concrete footings and mortar mixes as ordinary brickwork. The blocks are made in various different sizes, enabling you to construct a wall of any thickness, in a simple stretcher bond.
When building with concrete blocks, do not wet them before use as they can shrink when they dry causing the mortar joints to crack.
Inserting control joints
Control joints will need to be used in walls that are 6m (19ft 6in) in length or more. You will need to use a vertical control joint, which will allow for expansion in the wall.
- To do this, build un-mortared vertical joints at 6m (19ft 6in) intervals in a straight section of wall or against a pier and bridge the gap using galvanised metal strips.
- Then fill the rest of the joint with an all-purpose sealant (mastic).
In a situation where you need to insert a control joint in a partition wall, the best position to place it is along the edge of a door opening.
- To do this, you will need to fit it around the edge of a door lintel (the support above a door) and upwards to the ceiling.
- Fill the joint with mortar in the usual way, but rake it out to a depth of 18mm (3/4in) on both sides of the wall. Fill the groove you have created with all-purpose sealant keeping it flush with the face of the wall.
Constructing a partition wall
Building a partition wall is another common DIY challenge, which can seem a lot harder and complicated than it really is. Concrete blocks are a practical alternative to the non-load bearing partitions that are sometimes used. You need to plan ahead in terms of where to put the door (if you want one), and how big it’s going to be.
If you are going to fit a door into the partition wall, then you need to allow space for the wooden doorframe and lining, as well as the pre-cast lintel to support the masonry above the opening. The space above the lintel needs to be filled with concrete coursing bricks.
- Remove the skirting board on both sides of the room.
- Wall profiles should be fitted to the walls supporting each end of the partition wall. Make sure they are fitted straight to be sure that the new wall is perfectly upright. Before fitting the wall profiles use stud, pipe and cable detector to make sure there are no water pipes or electric cables at the fixing location.
- Tie string around two blocks and place one block against each wall profile to give you a guideline for laying the blocks against to complete the wall.
- Mark the position of the doorway
- To check where the doorway is going to go, lay the first layer of bricks across the floor un-mortared. Doing this also enables you to check their spacing.
- To lay each block, spread mortar with a brick trowel on the floor along the string line and onto the block, and position the block.
- Build stepped leads (the staggering of bricks in a step shape up to the wall profile) on each side of the wall
- Join the end blocks to the profiles with wall ties
Use the spirit level to check accuracy regularly
- Build another three courses of stepped leads, and leave the mortar to harden overnight before continuing with the wall. Continue to build the wall in the way.
- To build intersecting walls, butt the block at the intersection and anchor the structure using wire-mesh wall ties. If you are using hollow blocks, you should instead use metal tie bars with a curve at each end. Then fill the hollow block with mortar to embed the ends of the bars.
- When you come to inserting a lintel for the doorway, cut notches in the blocks with an angle grinder to bed the lintel between courses. Ensure the lintel is level.
- On reaching the ceiling whole blocks may not fit, so the gap between the final course of whole blocks and the ceiling will have to be filled in with cut blocks or bricks.
- Mortar has to be applied to the top of the cut blocks or bricks so they bond with the ceiling.
A final useful tip when working with concrete blocks is how to cut them correctly.
- If you do not have access to a masonry saw to cut through the block, score a line right round the block where it need to be cut.
- Using a club hammer and bolster chisel cut a grove around the block following the scored line.
- Repeat the process until you have quite a deep groove around the block. Then lay the block flat and apply a couple of heft blows to the bolster chisel with the hammer and the block will split evenly in two.