A masonry block is a building unit considerably larger than a brick, so that a wall is built with fewer units and fewer joints. Blocks are made from sand-lime (calcium silicate), aerated concrete (AAC), lightweight concrete with lava or expanded clay aggregate, or ordinary concrete. Most modern blocks are not laid in thick mortar beds but glued with a thin-bed mortar of 2 to 3 mm.
Types of masonry block
| Type | Properties | Use |
|---|---|---|
| Sand-lime block | Heavy and strong, good sound insulation | Loadbearing and separating walls, inner leaf |
| Aerated concrete block | Light, insulating, easy to saw | Non-loadbearing partitions, insulating masonry |
| Lightweight concrete block | Light, with lava or expanded clay aggregate | Partitions, including wet rooms |
| Dense concrete block | Heavy and strong in compression | Basements, retaining walls, foundations |
Advantages and limits
Advantages
- Much faster than brickwork: one block replaces six to ten bricks
- A flat wall, usually suitable for thin-coat plaster straight away
- Little construction moisture, since there is hardly any mortar in the wall
Limits
- Heavy blocks (sand-lime) cannot always be lifted by hand; large units are placed with block tongs or a mini-crane
- The base must be exactly level: with a 2 mm glue joint there is no room left to correct, so the first course is bedded in a thicker mortar bed
- Aerated concrete is stronger in compression than it looks, but locally fragile: use fixings designed for AAC
Method in brief
- Clean and level the substrate; bed and carefully level the first course in mortar
- Cut blocks to size with a hand saw (AAC) or a block saw
- Apply thin-bed mortar over the full bed face with a notched trowel or mortar sled
- Stack the blocks in bond — offset perpend joints by at least a quarter of the block length
- Tie the junctions with existing walls using wall ties or connection profiles
- Leave a permanently flexible joint at the head of the wall: the floor above can deflect, and a rigidly built-in wall will crack
Related terms
- Sand-lime brick
- Aerated concrete
- Masonry bond
- Thin-bed mortar
- Perpend joint
- Levelling course
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