Window and Door Expansion Profile Infinity (Plastic)

A window frame and the render around it behave differently. A uPVC frame in summer sun expands more than render does, and in winter it shrinks again. Sashes opening and closing and wind pressure add their own movement. If the render runs straight onto the frame, that stress will crack it sooner or later. A hairline crack forms along the frame and water gets in. In winter the water freezes and slowly damages the reinforcement layer and the insulation behind it.

The expansion profile prevents this. A self-adhesive foam tape on the back of the profile cushions the frame's movement. The mesh ties the profile firmly into the render, and the plastic bead gives a straight, sharp edge next to the frame. In practice it often happens that the render around windows cracks after the first winter. The cause is very often a missing or badly fixed profile.

Manufacturers of external wall insulation systems (ETICS) include connection profiles in their installation instructions. If the profile is left out, the system warranty may be at risk.

The profile goes on after the insulation boards are fixed and sanded where needed, and before the reinforcement layer is applied. Most systems follow a similar sequence:

1. Clean the frame of dust, mortar residue and old sealant. Degrease plastic with the cleaner recommended by the profile manufacturer. The surface must be dry.
2. Cut the profile to the length of each side of the window. The pieces meet in the corners with tight butt joints, with no overlap and no gap.
3. Peel the backing off the foam tape and press the profile onto the frame along its whole length. The tape must sit straight and without air bubbles on the visible face of the frame.
4. Apply base coat to the insulation next to the window and press the profile's mesh into it. In the corners, the mesh strips of neighbouring profiles overlap.
5. Place diagonal mesh patches at the corners of the opening to take the stress there. Then apply the full reinforcement layer with mesh, overlapping the profile's mesh.
6. Once the reinforcement layer has cured, apply primer and then the finishing render up to the edge of the profile.
7. Remove the protective film or tear-off strip only after the render is finished, if the profile has one.

The work is done in dry weather. According to most manufacturers, air and surface temperature should usually stay above +5 °C. The base coat should not dry in direct sun or strong wind.

Expansion profiles differ more than they seem at first glance. A few points are worth checking:

• Movement capacity: simple profiles handle only small movements, while more flexible types cope with larger movement in several directions. A more flexible profile makes sense for large windows, dark frames and south-facing walls.
• Protective film or strip: some profiles have a strip for attaching a sheet of film. This covers the window while the walls are rendered, so the glass stays clean and does not need taping.
• Frame material: the adhesive tape must hold on uPVC, timber or aluminium. For timber or painted frames, check that the manufacturer approves the profile for that surface.
• System compatibility: the profile, base coat, mesh and render should belong to one system or carry the manufacturer's approval. Mixing products from different makers often causes disputes later if something fails.

The insulation thickness usually does not decide which profile you need, because it sticks to the frame. With thick insulation and windows set forward in the wall, the reveals and the window sill need careful detailing as well.

The job goes fastest on a new build with new, clean windows and straight reveals. The profile goes on quickly and the mesh is bedded in together with the reinforcement layer.

More time is needed for:

• Old frames with leftover silicone, paint or mortar that must be cleaned thoroughly first
• Many small windows, because every opening has four corners and a lot of cutting
• Unusual shapes such as arched windows or sloping frames
• Uneven reveals where the insulation has to be levelled first
• Work from scaffolding or a lift, especially on blocks of flats

In a block of flats, the building management or owners' association arranges the insulation, not individual owners. For a house, check with your local building authority beforehand whether insulating the facade needs permission or notification under local building regulations.

• Fixing to a dirty or damp frame: the tape does not hold, the profile comes loose over time and a crack appears along the frame.
• Gaps at the joints: the pieces must meet tightly. Even a small gap in a corner turns into a crack later.
• Mesh laid dry: the mesh must be pressed into fresh base coat. If it just lies on the surface, the joint has no strength.
• No diagonal mesh at the corners: diagonal cracks run out from the window corners, and the profile alone cannot stop them.
• Render taken over the edge of the profile: the render then touches the frame and the flexible joint no longer works.
• Working in cold or rain: the base coat sets poorly and the tape grips less well at low temperatures.

At handover, look closely around each window and door:

• The profile is stuck down along the whole frame and does not lift anywhere
• The corner joints are tight, with no gaps and no overlapping profiles
• The render edge is straight and stops at the profile, not on the frame
• There are no cracks in the render next to the frame or at the corners of the opening
• The protective film has been removed and the frame is not scratched or dirty
• The window opens and closes without any problem
• The contractor can tell you which system and which profiles were used

It is worth checking around the windows now and then, ideally before winter. A small crack is easy to repair before water starts getting in.