Constructing Partitions up to 12.5 cm Thick

The method is similar for brick and aerated concrete. The main difference is how the units are joined. Aerated concrete is bonded with thin-bed adhesive, with joints usually no more than about 3 mm. Standard bricks are laid on mortar with joints of roughly 1 cm. Precision-ground bricks are laid on adhesive or foam, depending on the manufacturer.

1. Measure up and mark the line of the partition on the floor, walls and ceiling, including any door openings.
2. Check and clean the base. In a bathroom, or on a ground-floor concrete slab, lay a damp-proof strip under the first course.
3. Bed the first course in levelling mortar and set it carefully to the spirit level. Mistakes in the first course cannot be corrected later.
4. Lay the following courses with a proper bond, so the vertical joints are staggered by at least a third of the block length.
5. Tie into the existing walls with stainless steel flat wall ties set into the bed joints, usually in every second or third course.
6. Fit a lintel over the door opening with enough bearing on both sides, as specified by the manufacturer.
7. Stop roughly 1 to 2 cm below the ceiling and fill the gap with a flexible material such as expanding foam.

Before plastering, reinforcing mesh is embedded where different materials meet and at the corners of door openings. It greatly reduces the risk of hairline cracks appearing later.

Both materials suit an ordinary partition. Each has its own strengths.

• Aerated concrete blocks are light, can be cut with a hand saw, and chasing them for cables is easy. The wall goes up quickly and comes out very flat, so a thin coat of plaster or skim is enough. The downsides are weaker sound insulation and lower holding strength for heavy items, which need fixings designed for aerated concrete.
• Clay partition bricks are heavier and so block noise better. They suit a wall between a bedroom and a living room, or between two flats. They also hold kitchen cabinets or a water heater more securely. The work is a little slower, and when laid on mortar the wall needs a thicker coat of plaster.
• Gypsum partition blocks are also bonded with adhesive and give a smooth surface. In damp rooms, only moisture-resistant types should be used.

Why is aerated concrete often chosen even where brick would perform better acoustically? It is lighter, which helps with older floors and ceilings, and it is quick to work with. If quiet matters to you, ask about a thicker or heavier version of the partition.

The quickest job is a straight partition with no openings in an empty room with a level floor. The work becomes more demanding mainly when there is:

• An uneven or damaged floor that has to be levelled first
• Several door openings, corners, curves or an angled junction with a sloping loft ceiling
• Work in an occupied flat, with covering up and cleaning every day
• Material to carry up several floors without a lift
• Repair work needed on the surrounding walls before the new partition can be tied in
• A damp room where the base of the wall needs waterproofing

A non-load-bearing partition does not touch the structure, but it is still building work. Whether you need to notify anyone, or need a different kind of approval, depends on local building regulations and on your situation. Before you start, check with your local building authority rather than relying on general advice.

In a block of flats, let the building management or owners' association know in advance, especially because of noise, removing rubble and any work near shared services. Take care in older houses with timber joist floors: a heavy brick partition can overload them. Here it makes sense to have the floor assessed by a structural engineer. Any new electrical wiring in the partition must be connected by a qualified electrician.

• A first course that is not level, so the wall twists and the door frame does not fit properly
• A partition built tight to the ceiling, which cracks when the ceiling deflects
• Missing wall ties, leaving a vertical crack in the corner next to the old wall
• Adhesive joints that are too thick on aerated concrete, reducing both strength and flatness
• Plastering without mesh where brick meets aerated concrete
• Cable chases cut too deep or at an angle, which weaken the partition

A handy homeowner can build a non-load-bearing aerated concrete partition, given enough time and a good spirit level. Leave the electrics to an electrician, and if you have any doubt about the floor, ask a structural engineer.

1. Check with the building authority what the work requires and, in a flat, inform the building management.
2. Mark the line of the partition on the floor, walls and ceiling with a laser or a string line.
3. Clean the base of dust and remains of old layers.
4. Bed the first course in levelling mortar and check every block with a spirit level in both directions.
5. Let the mortar under the first course harden as the manufacturer advises.
6. Apply adhesive with a notched trowel to both the bed and the end faces, and lay the blocks with a staggered bond.
7. Set stainless steel ties into the joints where the partition meets the existing wall.
8. Fit the lintel over the door and leave a gap under the ceiling for foam.
9. Plane off any unevenness with an aerated concrete rasp and embed mesh over the joints before plastering.

• The wall is plumb and flat, checked with a long straightedge in several places
• The vertical joints are staggered, not lined up above each other
• Wall ties are visible or documented where the partition meets old walls
• There is a flexible gap under the ceiling, not a rigid fill
• The door opening has the right width and height for the planned frame
• The lintel bears far enough onto both sides
• In a bathroom there is a damp-proof layer under the first course
• Mesh is in place where materials meet, before plastering