Plastic Gutter Edge Trim for Roofing & Cladding

The corner is the most vulnerable spot on any facade. Bikes, ladders, wheelbarrows and footballs all end up hitting it. If there were only a thin layer of base coat and render over polystyrene or mineral wool, the edge would soon be chipped and broken. The bead gives the corner a rigid edge, and the mesh bonds it firmly to the base coat on both walls.

The second reason is appearance. Without a bead it is very hard to form a straight, crisp corner over the full height of a house. With a bead, the installer has a fixed edge to work the base coat and render against.

Corner beads are typically fitted:

• On the external corners of the building
• On the edges of window and door reveals
• On the corners of balconies, loggias and parapets
• On the underside edge of window heads, where a bead with a drip edge is used

Standard corner bead with mesh

This is the usual choice for right-angled corners. The main difference between products is the width of the mesh on each side. Wider mesh ties the corner more securely into the wall surface, so it is chosen for exposed spots that take more knocks.

Drip edge bead

This one goes on the underside edge of window heads, balcony slabs and any projecting parts. A small drip nose makes water drop off instead of running along the underside back towards the window or onto the facade. Wherever water runs off an edge, this bead replaces the standard one.

Flexible bead for other angles

For obtuse or sharp angles, for example on bay windows or curved walls, a flexible bead is used that can be bent to the shape.

PVC or aluminium?

Almost all insulation systems today use PVC. It does not corrode, does not react with the alkaline adhesive and is easy to cut. If you are using a certified insulation system, choose the beads the system manufacturer lists as part of it. Otherwise you risk problems with the warranty for the whole system.

The bead goes on after the insulation boards are bonded and anchored, but before the reinforcing mesh is embedded across the wall surface.

1. Rasp the corner of the insulation so both faces are flat and the edge has no steps.
2. Brush off the dust and rasping debris.
3. Spread base coat on both sides of the corner, slightly wider than the mesh on the bead.
4. Press the bead into the base coat and set it plumb with a spirit level or straightedge.
5. Trowel the base coat over the mesh so the mesh is fully embedded and nothing sticks out.
6. Butt the next length of bead tightly against the previous one and let the mesh overlap.
7. Embed the facade mesh across the wall so it overlaps the mesh of the bead, then apply the second layer of base coat.

At the corners of window and door openings, extra diagonal strips of mesh are added. Without them, the typical diagonal cracks running out from window corners appear.

The number and length of corners matter most. One long building corner is much quicker than dozens of short edges around small windows. Reveals take more effort because they are narrow and the bead often has to meet a window connection profile.

The job also takes longer with:

• Uneven insulation that has to be rasped flat first
• Unusual angles and curves
• Work from scaffolding at height, where every step is slower
• Bad weather, when the crew has to wait

On the other hand, when the beads are fitted as part of the same process as the base coat on the whole facade, the work runs smoothly without unnecessary downtime.

• Bead stuck onto dry insulation without base coat. It only holds at a few points and comes loose over time.
• Mesh not embedded. If the mesh is visible or sits on the surface, the base coat peels away around it.
• Beads overlapped. This leaves a bump on the corner that the render will not hide. The plastic parts should butt together. Only the mesh should overlap.
• Crooked corner. If the bead is not set with a level, it shows as soon as the render is on, especially in low side light.
• No drip edge above the window. Water then runs along the window head and the facade around the window stays dark and damp.
• Work in frost, rain or direct sun. The base coat does not cure properly and may crack. Most manufacturers specify a surface and air temperature of roughly +5 °C or more and recommend protecting fresh work from rain.

If you are insulating a garage, a garden building or the ground-floor part of a wall and can work from the ground, you can fit the bead yourself. Leave work from scaffolding and the facade of a whole house to the company doing the rest of the insulation.

1. Get the beads, base coat, trowel, spirit level and a knife for cutting plastic ready.
2. Rasp the corner of the insulation with a rasping board and brush off the dust.
3. Measure the length and cut the bead. At windows, keep the plastic part shorter and the mesh longer.
4. Mix the base coat according to the instructions on the bag.
5. Spread base coat on both sides of the corner.
6. Press the bead in, set it plumb with the level and trowel the mesh into the base coat.
7. Scrape off excess base coat so no lumps form on the edge.
8. Let it dry as the manufacturer specifies before continuing with the mesh on the wall surface.

Inspect the corners before the render goes on. After that, mistakes are hard to put right.

• The corner is straight over its full height, checked with a straightedge or level
• The mesh of the bead is nowhere visible and is fully embedded in the base coat
• Bead lengths butt together without bumps or gaps
• The facade mesh on the wall overlaps the mesh of the bead
• Diagonal mesh strips are in place at the corners of windows
• A drip edge bead is fitted above windows and on underside edges
• The bead does not sound hollow when tapped and does not move