What is simili?
Simili, short for simili-pierre (also pierre-simili or fausse-pierre), is a facade render that imitates natural stone. The term is used mainly in Belgium and the Low Countries. A lime and/or cement-based render is applied over brickwork and finished so that the facade looks as if it were built of dressed stone blocks. In English the closest equivalent is stucco or render lined out to imitate ashlar. The name comes from the Latin simulare (to imitate) and the French pierre (stone).
Composition and technique
Simili mortar consists of a binder (lime, cement or both), aggregate, water and pigment, sometimes with mica added to mimic the sparkle of real stone. Its quality improved markedly from the mid-19th century as Portland cement became more widely available. To strengthen the illusion of blockwork, recessed or incised joints were usually drawn into the render. Plinths, string courses and window surrounds were often executed in the same way.
Difference from cast stone
Cast stone is a solid unit cast or pressed in a mould and then built in as a whole, for example as a sill or window surround. Simili is a layer a few centimetres thick applied on site over the masonry. Tap it, and a detached simili layer sounds hollow; a cast stone block does not.
| Cast stone | Solid unit cast or pressed in a mould, then built in as a whole (for example a sill or window surround). A cast stone block does not sound hollow when tapped. |
|---|---|
| Simili | Layer a few centimetres thick applied on site over the masonry. A detached simili layer sounds hollow when tapped. |
Application: repairing simili
- Tap-test the facade. Sound the whole surface systematically for hollow areas. Loose sections can fall and should be removed in good time.
- Find the cause of cracks. Cracks often come from settlement, rusting ironwork or moisture behind the render. Simply filling them solves nothing.
- Watch for moisture problems. A dense, cement-rich layer over old lime-mortared brickwork can trap moisture, leading to frost damage, spalling and damp patches inside.
- Repair like with like. Match the repair mortar to the original in strength, vapour permeability, colour and texture; if in doubt, have a sample analysed first. A mortar that is too hard will crack away or damage the surrounding material.
- Do not seal it with paint. Vapour-tight paint traps moisture and hides the stone effect. If it must be painted, use a breathable mineral paint.
- Reinstate the joint pattern. Recut the recessed joints on the same grid, or the block pattern will no longer read correctly.
On listed or protected facades, consult the local conservation authority before starting work.
Related terms
- Facade rendering
- Cast stone
- Lime mortar
- Natural stone replacement
- Listed building
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