How to build a wall with lightweight concrete blocks

What is done before laying starts?

Redblok lightweight concrete block is for non-loadbearing walls in reinforced concrete or steel frames. It is used for interior partitions and for infill walls built within the frame. It is not used for walls that carry floor or roof loads.

The density class is chosen before the wall starts. The typical block band is 500–800 kg/m³, which means KB500 to KB800. Across that range, the compressive strength target rises from 1.5–2.5 MPa to 4.0–6.0 MPa, and the thermal conductivity target from 0.12–0.14 W/mK to 0.20–0.24 W/mK. These are design targets, confirmed by laboratory testing. Wall height, hanging loads and, for external walls, the heat calculation to TS 825 (the Turkish thermal insulation standard for buildings) decide the class together.

Blocks wait on their pallets, off the ground and covered. Blocks that have taken rain are not laid while wet. The slab is cleaned of dust, oil and loose material. The wall line and door openings are marked on the slab and the frame.

How are the courses laid and jointed?

A wall is only as true as its first course. Level differences in the slab are taken up by a bed of levelling mortar under the first course. Blocks are set into this bed, tapped down with a rubber mallet and levelled in both directions. Alignment is checked with a string line or laser. A small error in the first course grows as the wall rises. Masons then try to hide it with thick joints in the upper courses, and joint quality suffers. Whether a damp-proof layer is needed at the base of ground-floor walls and in wet rooms is decided in the architectural detail.

The jointing material depends on the block's dimensional accuracy. Blocks with tight tolerances are laid with thin-joint adhesive; blocks with wider tolerances use conventional masonry mortar. Which one to use, and at what joint thickness, is stated in the manufacturer's instructions and the design. The two methods are not mixed in one wall.

Lightweight concrete block is absorbent and can draw water out of fresh mortar quickly. Mortar that loses its water bonds poorly. Whether to pre-wet the blocks and how water-retentive the mortar must be both follow the instructions. Bed and head joints are filled completely, because an empty joint leaves a weak spot and a path for sound. Head joints are staggered so they do not line up with the course below. Excess mortar or adhesive is cleaned off before it hardens.

How are blocks cut and chases made?

Lightweight concrete block is cut with a saw. End and corner pieces are measured and cut, not broken. A hand saw or a power saw with a suitable blade can be used. Cutting makes dust, so use dust extraction, a dust mask and eye protection. Cut pieces are sized so they do not upset the bond pattern.

Electrical and plumbing chases are cut with a wall chaser once the wall is built and the joints have hardened. Vertical chases are preferred. Long horizontal or diagonal chases weaken the wall section. Chase depth and limits on horizontal chases come from the design and the manufacturer's instructions. Once the pipes are in, the chase is filled with repair mortar. For hanging loads such as cabinets, basins and worktops, choose plugs and anchors suited to lightweight block walls.

How is the frame connection made?

An infill wall is detailed as a separate element inside the frame, not as part of the structure. A flexible joint is left between the top of the wall and the beam or slab soffit. This joint limits how much beam deflection loads the wall. It also reduces how much the frame squeezes the wall in an earthquake. Flexible joints are used at column and shear wall faces too. Packing these joints with rigid mortar is a common site mistake.

A flexible joint does not mean leaving the wall free to topple. Ties and anchors to columns and beams are placed to the design. Where needed, intermediate bond beams and posts are added. Out-of-plane stability of infill walls in an earthquake is resolved in the structural and architectural design under TBDY 2018, the Turkish Building Earthquake Code. It is not a decision made by eye on site. Lintels over doors and windows are also defined in the design. Lower wall mass, for its part, reduces the seismic mass entering the structure in a TBDY 2018 analysis.

What happens before plastering?

Where blocks meet concrete or steel members, different materials come together. These lines are the most crack-prone places in the plaster. Before plastering, these junctions and the filled service chases are covered with plaster mesh lapping onto both sides. The plaster must suit a low-strength, absorbent surface. Whether a primer is needed is stated by the plaster manufacturer.

The known weak point of non-autoclaved concrete is lower strength and higher drying shrinkage at the same density. We developed the Redblok mix with that in mind, and we measure it in every batch. On site, moisture control is what matters most. The volumetric water absorption target for KB500–KB800 is 10–16%. Plastering a wall before it has dried enough can lead to cracks as it dries. External faces are protected from rain by render or cladding. Wet rooms get a waterproofing detail before tiling.