Mesh Reinforcement for Masonry Partitions

Not every partition needs mesh over its whole surface. In some situations, though, the risk of cracking goes up noticeably, and the mesh is worth it:

• New builds: the masonry is still drying out and the building moves slightly during its first years, so partitions work harder than in an older house
• Mixed materials: where brick meets aircrete block, or masonry meets a concrete column or lintel, each material reacts differently to changes in temperature and moisture, and a crack often appears along the joint
• Large areas and thin partitions: a long, thin partition flexes more easily, so its surface is more likely to crack
• Renovations: an older partition with a sound but uneven or cracked surface gets a consistent, well-bonded base
• Around openings: the corners of doors and passageways are where cracks show up first, so mesh goes in here even when the rest of the wall is left without it

With partitions built from precision blocks on thin joints, the mesh is often part of a thin-coat skim system that replaces traditional plaster. With a thicker lime or sand and cement plaster, the mesh goes into the upper part of the coat, or only the high-risk spots are reinforced.

A good result starts with the bricklaying. If the partition leans or has mortar sticking out of the joints, the base coat and mesh will not hide it. They will simply follow it. The work itself goes like this:

1. Preparing the surface: dust, mortar residue and grease are removed. Larger hollows and chipped areas are filled and levelled first.
2. Priming: absorbent backgrounds, typically aircrete, get a coat of primer so the base coat does not dry too fast and bonds properly.
3. Reinforcing high-risk spots: diagonal strips of mesh go into the corners of openings, and a strip overlapping both sides covers each joint between different materials.
4. First layer of base coat: the adhesive is spread over a band of wall roughly as wide as the mesh, usually with a notched trowel.
5. Embedding the mesh: the mesh is laid from the top down and pressed into the wet base coat with a trowel, working from the centre outwards, without creases or air pockets. Neighbouring strips overlap by roughly 10 cm.
6. Second layer: while the first layer is still wet, a further thin coat goes on to cover the mesh completely and level the surface.
7. Curing: drying time depends on the coat thickness, the temperature and the humidity in the room. Only then does the finishing skim, plaster or paint follow, according to the manufacturer's instructions.

One important detail: the mesh belongs inside the base coat, not directly on the masonry. Ideally it sits in the upper third of the layer. If it is stuck onto the bare wall and the adhesive only goes over the top, it hardly reinforces anything.

For internal partitions, the usual choice is glass-fibre mesh with an alkali-resistant coating. Cement and lime products are alkaline, and untreated glass would gradually lose its strength in them. Interior walls usually take a lighter mesh than external wall insulation systems, but the base coat manufacturer's recommendation is what counts.

The base coat should be designed for embedding reinforcing mesh and suitable for the background. In bathrooms and kitchens that will be tiled, choose a product that tolerates moisture and that the tile adhesive manufacturer approves as a substrate. It helps to stick to one system from primer to finishing coat, so the layers are compatible with each other.

The condition of the wall has the biggest effect on how demanding the job is, and therefore on its cost. A straight, clean partition of precision blocks is quick to mesh. A wall that is out of line, has crumbling joints or old plaster residue needs more preparation. Lots of openings, corners, recesses and electrical boxes also add time, because the mesh has to be cut around them and overlapped carefully. Taller walls need scaffolding or a mobile platform. A less visible but important factor is moisture in the masonry: there is no point rushing onto a wet new build, as the base coat may not cure properly.

• Mesh without overlaps or with gaps: a straight crack later appears exactly along the unreinforced joint
• Mesh laid directly on the masonry: it has nothing to work in and easily peels away together with the coat
• Mesh showing through: the top layer is too thin, and after painting you can see the mesh pattern
• Creases and bubbles: these appear when the mesh is pulled from the edge or pressed into a coat that has already started to set
• No diagonal strips at doors: a crack running from the corner of an opening is one of the complaints seen over and over in practice
• Working in the wrong conditions: in a cold or overheated room, or in a direct draught, the base coat cures poorly

It is also worth knowing that mesh does not stop everything. A crack where the partition meets the ceiling often forms because the floor or ceiling above deflects under load. There, a movement joint or a flexible connection is usually the answer, rather than relying on mesh. If diagonal or growing cracks appear in the wall, the problem is not the surface, and it is sensible to call in a structural engineer.

You can handle this job yourself if you are patient and work from a low, stable platform. For your first attempt, pick a small wall, such as one in a storeroom, and work calmly strip by strip.

1. Clean the wall of dust and mortar residue, and fill larger holes beforehand.
2. Apply primer and let it dry as instructed.
3. Cut the mesh into strips to the height of the wall and prepare smaller pieces for the corners of openings.
4. Embed diagonal strips at the door corners and a strip over any joint between different materials.
5. Mix the base coat as the manufacturer specifies and let it stand briefly.
6. Spread the base coat with a notched trowel over the width of one strip.
7. Lay the mesh from the top and press it in with a trowel from the centre outwards.
8. Continue with the next strip, overlapping by roughly 10 cm.
9. Cover the mesh with a thin layer of base coat while the first layer is still wet, and smooth it off.
10. Let the wall cure before applying any further coats.

If you come across electrical cables while chasing the wall or stripping old plaster, stop work. Any changes to the wiring must be carried out by a qualified electrician. In a flat, let the building management or owners' association know in advance, especially if the preparation will be noisy. If the job also involves building a new partition or altering the structure, check with your local building authority what local building regulations require.

When you inspect the wall, look at it in raking light, for example with a torch held flat against the surface. This shows up unevenness that disappears in normal light.

• The mesh does not show through or stand proud anywhere
• There are no bubbles, creases or flaking areas on the surface
• Diagonal strips have been embedded at the corners of doors and passageways
• Joints between different materials are covered with mesh overlapping both sides
• The surface is flat, with no obvious hollows when you hold a straightedge against it
• The areas around boxes and edges are neatly finished, and the mesh has not been cut short there
• The contractor has told you which materials were used and when the next coat can go on