Masonry work: cost per m² 2026 and the process

Before you choose a material, ask yourself a simple question: what does this wall have to do? One wall carries the floor above, another keeps the heat inside the house, a third keeps the neighbours' noise out, and a partition often just divides a room. Each material handles these jobs differently, and each one is laid in its own way.

• Fired clay blocks: ceramic blocks with holes running through them. Most now have ground bed faces, meaning the top and bottom are ground flat, so they are laid on a thin layer of mortar. They are strong, hold heat well and are vapour permeable, which means water vapour can pass through the wall.
• Aerated concrete: lightweight white blocks. They are easy to cut and can be laid very accurately. They insulate very well, but because they are light, they do less to stop sound. If you want to hang kitchen units or a heavy shelf on this kind of wall, buy fixings made for aerated concrete.
• Calcium silicate blocks: heavy, strong and able to carry a lot of load. Their weight is what helps them block sound, so they are often used for party walls between flats and anywhere quiet matters. On their own, though, they do little to keep heat in.
• Concrete blocks and hollow formwork blocks: these belong in foundations, cellars, retaining walls and garden walls. Formwork blocks are hollow. Reinforcement goes into the hollows, which are then filled with concrete.

Do not mix different materials in one wall without thinking it through. Each one expands and settles in its own way, and sooner or later a crack appears where they meet. If you cannot avoid a combination, reinforce the junction with mesh embedded in the plaster.

Precision blocks are laid in thin-bed mortar or adhesive. That joint is only a few millimetres thick, so you cannot use it to even out an uneven base. This is why the first course goes into conventional mortar and is carefully levelled along the full length of the wall. Why so much care? Any error in the first course is carried into every course above it, and by the time you reach the ceiling, a small error has become a big one.

For external walls on foundations and walls that stand directly on the ground, a damp-proof course goes under the first course. It stops water rising from the foundations into the masonry. In practice this layer is often forgotten on extensions and garages. A few years later, damp patches show at the bottom of the wall and the plaster starts to fall off.

Blocks are laid in a bond, which simply means the vertical joints must not line up one above the other. The block manufacturer states how far each block should overlap the one below. For standard blocks it is at least a few centimetres. If the blocks have a tongue and groove on their ends, leave the vertical joints without mortar: the blocks just slot into each other.

When a flat is renovated, new partitions are usually built from aerated concrete or clay partition blocks. You normally cannot bond a new partition into the existing wall, so it is connected with wall ties or steel straps. These are set into the bed joints as the partition goes up.

Leave a gap between the top of the partition and the ceiling and fill it with something flexible, such as expanding foam or a resilient strip. The reason is that a floor slab bends slightly under load. If you wedged the partition tight under it, the slab would press down on the partition and crack it. Later, cover the joint with mesh-reinforced plaster or acrylic sealant.

A masonry partition is heavy. In a concrete panel block of flats, and in older houses with timber joist floors, check first whether the floor can carry the extra weight. On a timber floor, a plasterboard partition is often the more sensible choice.

Openings and lintels

Above every door and window there is a lintel. It carries the masonry above the opening and passes the load into the wall on each side. It has to be long enough to sit firmly on the masonry at both ends. In a partition a light lintel is enough. An opening in a load-bearing wall needs a structural lintel, sized by a structural engineer.

Cutting a new opening in a load-bearing wall, or widening an existing one, is structural work. A load-bearing wall holds up the floors and storeys above it. If the opening is made without temporary support and without the right lintel, cracks can appear, and sometimes more serious damage. Before any such work, you need a structural engineer. They assess the wall and specify the lintel, the temporary support and the order in which the work is done.

In concrete panel blocks of flats, the load-bearing panels are altered only in exceptional cases, and always with a structural engineer's approval. In any block of flats you also need consent from the building management or the owners' association. Structural alterations come under local building regulations, and the rules differ from country to country and sometimes between regions. Check with your local building authority what your plans require before you start. Do not assume a quick notification is enough. Sorting out approval for work that is already finished is usually far harder and costs a lot more time and nerves.

Traditional plaster goes on in two coats. The base coat levels out the masonry and the finish coat gives a fine surface. Today, single-coat plasters applied by machine are common: they are sprayed on and smoothed in one go. Before plastering, plaster beads are fixed to the wall to set a flat plane, and angle beads go on the external corners so they come out straight and resist knocks.

• Lime and lime-cement plaster: lets vapour pass through and stands up well to wear. It suits living rooms, bathrooms and façades. Lime naturally discourages mould and helps to even out humidity in the room.
• Gypsum plaster: gives a very smooth surface without a separate finish coat and dries quickly. It belongs in dry living spaces. Keep it out of showers and other wet areas.
• Renovation plaster: made for damp, salt-laden masonry. It has large pores, and the salts settle in them instead of breaking the plaster apart.

Plaster needs time to cure. For base coats, a common rule of thumb is roughly one day per millimetre of thickness, but the exact time is given by the manufacturer on the bag. If you paint or tile too early, expect stains, peeling paint and cracks.

Sooner or later, every flat renovation raises the question of what to do with the old plaster. If it is sound and well stuck to the masonry, it is enough to repair the damaged spots and skim the wall. A skim coat evens out small irregularities and leaves a smooth surface ready for paint. You avoid demolition and you do not wait weeks for the wall to dry.

How do you know whether plaster is sound? Tap it. Spots that sound hollow, different from the area around them, should be knocked off and filled. If a large part of the wall sounds hollow, or the plaster crumbles or is soaked with damp, it makes more sense to strip it all and replaster. A skim coat on a weak background will eventually come away, taking the old plaster with it.

In old houses, layers of paint often hide limewash and clay plasters. A modern skim coat will not necessarily stick to them, so try a small test area first. For historic buildings, ask a conservation specialist for advice. In buildings from the middle decades of the last century, some textured wall and ceiling coatings may contain asbestos. If you are unsure, have a sample tested before you sand or scrape, and leave any removal to a licensed professional.

Older houses often have no working damp-proof course, so moisture from the ground rises into the walls. The signs are damp patches just above the floor, white salt deposits and plaster falling off. New plaster on its own will not fix this. First you have to stop the water getting in, for example by inserting a new damp-proof course after cutting through the wall, by chemical injection, or by improving drainage around the house.

A common mistake is to repair a damp wall with cement plaster or a paint that does not breathe. The moisture cannot dry out through them, so it climbs even higher up the wall. Damp old masonry needs lime or renovation plasters that let vapour through and allow the moisture to escape.

Mortar and adhesive need water to harden. When that water freezes, it damages their structure and the joint loses strength. So do not lay blocks below the temperature the manufacturer states, usually around +5 °C, and never on frozen blocks. Cover fresh masonry overnight and whenever rain is coming. Rain would wash out the mortar and soak the top of the wall.

If plaster has come off in just one small spot, for example where a wall plug was pulled out or next to a door frame, you can repair it yourself. You need a small hammer, a brush, repair mortar, a trowel and a little patience.

1. Tap off all loose plaster around the damaged spot with a small hammer until the edge is firm.
2. Brush the dust off the masonry and dampen it so the new plaster does not dry too fast.
3. For a deeper hole, apply the repair mortar in layers and let each layer stiffen before the next.
4. Rule off the final layer with a straightedge or trowel so it sits flush with the surrounding wall.
5. Once it has started to set, smooth the surface with a damp trowel or sponge float so the texture matches the rest of the wall.
6. For a crack where different materials meet or above a door, press a strip of glass-fibre mesh into the wet mortar.
7. Let the repair cure for the time given on the packaging, then prime and paint.
8. If plaster keeps falling off near the bottom of the wall, look for damp in the masonry as the cause.

• The walls are plumb and flat, checked with a spirit level and a long straightedge
• The masonry is bonded and the vertical joints do not line up above each other
• Every opening has a lintel that sits firmly on the masonry at both ends
• The gap between the partition and the ceiling is filled with a flexible material
• The plaster is flat, with no cracks, hollow spots or straightedge marks, and the corners are straight
• For any work on a load-bearing wall, you have the structural engineer's assessment and the documents from the building authority