In short
- A modern thin-coat system has: prepared substrate, beads, base coat with embedded mesh, primer, then topcoat.
- Alkali-resistant glass-fibre mesh spreads stress and resists cracking.
- Beads form corners, edges and stop lines, including a base bead above the damp-proof course.
- All components should come from one manufacturer's system.
The layers
- Substrate preparation: remove loose material, repair brickwork, treat algae, check for damp and hollowness.
- Beads: corner, stop, bellcast or base, and movement beads, in stainless steel or PVC.
- Base coat: a cementitious or polymer-modified coat, typically around 6 mm or as specified.
- Mesh: alkali-resistant glass-fibre mesh embedded in the base coat, with extra diagonal pieces at opening corners.
- Primer: tinted to the finish colour, controls suction and improves bond.
- Topcoat: silicone, acrylic or mineral finish, 1–2 mm.
Monocouche systems differ: a single thick coat, sometimes over a base or scratch coat on difficult substrates.
What to look for on site
- Beads fixed straight and plumb.
- Mesh fully embedded, not visible at the surface.
- Base stop line at least 150 mm above ground.
- Adequate curing time between coats.
Why system integrity matters
Manufacturers test their products together: the base coat's alkalinity with the mesh, the primer with the topcoat, the beads with the render thickness. Swapping a component, such as a cheaper mesh or another brand's primer, can cause poor bond or cracking and usually voids the manufacturer's guarantee. See render guarantees.
Beads in more detail
| Bead | Where | Job |
|---|---|---|
| Angle or corner bead | External corners | Sharp, straight, protected arris |
| Stop bead | Edges, abutments | Neat, defined edge |
| Bellcast or base bead | Bottom of render | Throws water clear, stops render above DPC |
| Movement bead | Long walls, junctions | Absorbs expansion and contraction |
| Reveal bead | Window and door reveals | Clean edge to frames |
Stainless steel and PVC beads do not rust. Old galvanised beads can corrode and push render off, a common cause of failure on older jobs.
The base coat is the real structure
The topcoat gets the attention, but the base coat carries the load: it levels the wall, holds the mesh, spreads stress and gives the finish an even surface. Too thin, and the mesh sits at the surface and shadows through. Too thick in one pass, and it can slump or crack. Manufacturers specify thickness ranges, and a good crew checks them.
Monocouche and lime differ
Monocouche combines levelling and finish in a single thick layer, sometimes over a scratch coat on difficult backgrounds. Lime builds up in several coats, each weaker than the last, with long curing between. See thin-coat vs thick-coat.
Questions people ask
What is render mesh for?
It reinforces the base coat, spreading stress so cracks do not form at weak points such as window corners.
What is a bellcast bead?
A bead at the base of the render that kicks water away from the wall, placed above the damp-proof course.