Walk past a half-finished building, and you might spot a thin vertical crack where a concrete column meets a brick wall. The crack often develops because concrete and masonry respond differently to temperature changes, moisture, and structural movement. The plaster layer between them cannot always accommodate the resulting stress. Chicken mesh, a lightweight wire mesh fixed across the junction before plastering, helps reinforce the joint and reduce the risk of cracking.
Why does plaster crack, and where is chicken mesh needed?
Plaster cracks along joints because the backing materials expand, shrink and absorb moisture at different rates. Concrete moves roughly 10 to 12 µm per metre per °C, clay brick about 5 to 8. Add drying shrinkage in new concrete and moisture swelling in brick, and the joint line becomes a hinge. A rigid, unreinforced coat of cement mortar can't follow it, so it splits.
Mesh is worth fixing in these places:
| Location | Why it cracks | Mesh detail |
|---|---|---|
| RCC column to masonry | Different thermal and shrinkage movement | 300 mm strip over the full height |
| Beam soffit to wall top | Beam deflects, wall settles | 300 mm strip along the junction |
| Chases for conduit and pipes | Patch mortar shrinks away from the old wall | Strip 100 mm wider than the chase each side |
| Window and door corners | Stress concentrates at the opening corner, cracks run at about 45° | Diagonal piece, roughly 300 × 600 mm, over each corner |
| Mixed backing (brick, block, concrete patch) | Suction and movement change across the wall | Full-surface lath or fiberglass mesh |
| Old plaster or timber lath repair | Weak key to the substrate | Galvanized mesh fixed to sound backing |
A plain, uniform brick wall with no joints between materials doesn't need mesh. Putting it everywhere adds cost and labour without stopping anything.
Mesh also won't fix a moving structure. If the crack is wider than about 1.5 mm or keeps growing, look for settlement or an overloaded member first. On masonry retaining wall types, face plaster cracks mostly because of drainage and soil pressure, so check those before blaming the plaster.
What is the difference between chicken mesh, expanded metal lath and welded mesh?
Strictly, chicken mesh is hexagonal wire netting: wires twisted around each other in pairs to form a honeycomb. It's flexible, light and sold in rolls. Site talk is looser. In many countries the same name gets used for expanded metal lath, welded wire and even fiberglass. Their jobs overlap, but they behave differently once buried in mortar, so it pays to know which one you're actually buying.
What are the types of mesh used for plastering?
| Type | Typical spec | Best use | Limit |
|---|---|---|---|
| Hexagonal wire netting (true chicken mesh) | 20–25 mm hex opening, about 0.7–1.0 mm galvanized wire | Joint strips, chase patches, small repairs | Sags if left slack. Thin wire rusts quickly in wet exterior coats. |
| Expanded metal lath | Diamond openings, rated by weight per m² (or lb/yd²), flat or self-furring | Full-surface cement plaster, ceilings, stucco, curved work | Sharp edges. Flat types need furring so mortar gets behind. |
| Welded wire mesh | From fine 12–25 mm grids in thin wire to 50 mm stucco mesh in heavier wire | Rigid backing, exterior cement render | Welds can snap if bent too tightly on site. |
| Alkali-resistant (AR) fiberglass mesh | 4–5 mm square, polymer-coated, commonly around 145 g/m² on facade systems | Thin coats, insulation facades (ETICS), gypsum and cement skim over joints | No rust, but also no stiffness. It crack-controls, it doesn't carry a thick coat. |
| Plastic (PP/PVC) mesh | Square or rectangular openings, 10–20 mm and up | Light interior work, screeds, paint-coat repair | Low stiffness. Weak crack control in cement plaster, poor outdoors in sun. |
Whatever the metal type, the wire should be zinc-coated. Mesh sold as "black" or lightly coated is cheaper because it's the part that rusts first.
How do you choose the right mesh?
Two quick checks on top of that. Exterior or damp wall: choose heavier galvanizing, or go with AR fiberglass. Interior dry wall with a thin coat: wire near the surface will rust-stain the paint, so fiberglass is the safer bet.
How do you fix chicken mesh before plastering?
- Prepare the joint. Rake out loose mortar, fill gaps solid, wet the surface. Mesh over an empty gap just bridges a void.
- Cut strips. Centre them on the joint, 150 mm either side. Work from a roll in 2 to 3 m lengths so you can keep it tight.
- Fix. Galvanized nails with washers into brick joints, masonry nails or plugs into concrete, spaced 150 to 200 mm and staggered. Flatten the mesh as you go. A bulge means mortar can't wrap the wire.
- Lap. About 100 mm at ends. For lath, follow the maker's lap sheet.
- Bury it. Push the base coat through the openings with firm trowel pressure so the wire is wrapped, not just painted over.
- Cure the base coat. Keep it damp for a few days, then apply the finish coat. Skipping the base coat and floating a thin finish straight over the mesh is the most common way to telegraph the pattern.
A word on thin coats. If your whole plaster is only 12 mm, wire has almost nowhere to hide, and it ends up close to the face where moisture reaches it. In that case use fine-wire strips only at the joints, or switch to fiberglass. The usual advice is that exterior metal mesh needs generous cover on both sides of the wire. The exact figure depends on your spec, so check it.
How much mesh do you need?
For joint strips you measure length of joint, not wall area. Say one room is 4.0 × 3.5 m with a 3.0 m storey height:
- 4 column joints × 3.0 m = 12 m
- Beam soffit junction around the room = 15 m
- Total joint length = 27 m
- Strip area = 27 × 0.30 = 8.1 m²
- Add 10% for laps and cut waste = about 8.9 m²
- Nails: 27 m ÷ 0.175 m ≈ 154 per row × 2 rows ≈ 310 nails, plus washers
Full-wall lath is different: take net wall area, deduct openings, and add 10 to 15% for laps. Get the area quickly from the wall area calculator. For the mortar volume behind it, see plaster quantity for walls or run the numbers in the plaster calculator. If you're pulling a whole bill of materials off a plan, start with material quantities from drawings.
What mistakes bring plaster cracks back?
- Mesh too narrow. A 100 mm strip stops being useful once the crack wanders outside it.
- Slack mesh. Loose wire moves with the plaster instead of restraining it.
- No base coat cure. Finish coat applied over a green, shrinking base cracks anyway.
- Bare steel in contact with wet plaster for long. Cut ends and nail heads rust first. Touch them with zinc-rich paint on exterior work.
- Mixing metals. Aluminium accessories against cement and steel nails set up corrosion.
- Using mesh to hide movement. Active structural cracks come back through any plaster.
Which standards apply?
Names change by country, so match the one your project spec calls up. Common references: ASTM C847 (expanded metal lath), ASTM C1032 (woven wire plaster base), ASTM C1063 (installing lathing and furring for plaster), BS EN 13658-1 and -2 (metal lath for internal and external plastering), and ASTM A641 (zinc-coated wire). For fiberglass in facade systems, the system supplier's approval document governs the mesh weight and laps.
Frequently asked questions
Is chicken mesh necessary for plastering every wall?
No. Use it where two materials meet, over filled chases, at opening corners and on repairs. A uniform brick wall plastered normally doesn't need it.
How wide should the strip be at a column-wall joint?
About 300 mm, so 150 mm each side, fixed every 150 to 200 mm.
Does chicken mesh rust inside plaster?
Galvanized mesh buried in dense mortar lasts a long time. Rust starts when wire sits near the face, the zinc coat is thin, or the wall stays wet.
Is fiberglass mesh better than metal?
For thin coats and insulation facades, yes, provided it's alkali-resistant. For thick cement coats that need a stiff reinforcement, metal lath wins.
Which side does the mesh go on?
The face being plastered. Fix it over the joint, then bury it in the first coat.
Bottom line: pick the mesh by location first, galvanizing second, price last. A 300 mm strip nailed properly across the joint costs very little next to re-plastering a cracked wall.