A masonry unit is the collective term for any building element laid in mortar or thin-bed adhesive to form masonry. The best known is the clay brick, but sand-lime brick, concrete block, aerated concrete and natural stone blocks all belong to the same family. Standards and product data sheets call such an element a masonry unit.
The main types
| Type | Raw material | Typical use |
|---|---|---|
| Clay brick | Fired clay | Outer leaf, facing work, facades |
| Sand-lime brick | Lime and sand, autoclaved | Inner leaf, loadbearing and separating walls |
| Concrete block | Cement, sand, aggregate | Facades, retaining walls, basements |
| Aerated concrete | Cement/lime, sand, aluminium powder | Non-loadbearing partitions, insulating masonry |
| Lightweight block | Cement with lava or expanded clay | Partitions, including wet rooms |
How to choose
- Compressive strength — for loadbearing work, the declared strength of both unit and mortar must match the loads; always have this calculated
- Water absorption and frost resistance — external work needs a frost-resistance class suited to the exposure; using an internal-quality unit outside is a classic mistake that shows up as frost damage after one winter
- Format — the size sets the course gauge and therefore the whole dimensional plan of the elevation
- Colour, texture and form — handmade, extruded or moulded units each give a different appearance
- Suction — a highly absorbent unit draws water out of the mortar; wet the units in warm weather, or the mortar will bond poorly
Laying tips
- Take units from several packs at once while laying, so colour variation between production batches is spread evenly over the elevation
- Do not lay in frost or when night frost is forecast; fresh mortar that freezes never gains strength
- Cover fresh masonry against rain: washed-out mortar leaves permanent lime staining
- Match mortar and unit: a joint harder than the unit will damage a soft brick
Related terms
- Brick
- Sand-lime brick
- Concrete block
- Masonry bond
- Masonry block
- Mortar
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