How thick is render?

Question

Can anyone explain the thickness I should go for and why? This is for an external wall

Stevie · Answer

For a standard sand and cement external render, total thickness is normally around:

• 16–20mm total
– 10–12mm base coat
– 6–8mm top coat

If it’s a thin coat system (silicone/acrylic render), it can be much thinner, typically:

• 3–6mm over insulation board
• Around 1.5–3mm finish coat

Thickness depends on:
• The condition of the wall
• Whether it’s going over brick, block or insulation
• Exposure to weather

You don’t usually “choose” the thickness — it’s determined by the system being used and manufacturer guidelines.

If you’re unsure, ask the installer what system they’re quoting for and the full build-up.

Neville · Answer

Scratch coat, 6to8mm, topcoat around the same, depending on straight the surface is.

Gary · Answer

I normally go for a roundabout 20 mil that’s what means I use so I have to come flush to them

Aaron · Answer

Hi June,

Depending on the render (sand & cement) or monchouce-/silicone render it can range as a general guide it will be 12-15mm (sand and cement up to 25mm in some case)

It's thickness is to keep out the elements protects from moisture, cracking, delaminating.

How this helps

Aaron The Plasterer

Gioni · Answer

Cavity Walls (Standard Modern Build)
This is the most common method for houses. It consists of two layers (leaves) with a gap in the middle.  
• Recommended Thickness: 300mm to 350mm total.
• The Breakdown: * 100mm outer leaf (brick or stone).
• 100mm–150mm cavity (filled with insulation).
• 100mm inner leaf (concrete or aerated blocks).
• The "Why": The cavity prevents moisture from "bridging" from the outside to the inside, while the thick insulation layer is mandatory in most regions to meet modern energy efficiency standards.
2. Solid Timber Frame
If you are going for a sustainable, breathable build, timber is the way to go.
• Recommended Thickness: 250mm to 300mm.
• The "Why": Timber itself is a decent insulator, but you need depth to pack in high-performance mineral wool or sheep's wool. Because there is no "hollow" cavity like a brick wall, you can save a little bit of floor space while achieving the same warmth.
3. Solid Masonry (Old School or Tropical)
Used primarily in warmer climates where "thermal mass" is more important than insulation, or in historic renovations.
• Recommended Thickness: Minimum 215mm (9 inches).
• The "Why": A single skin of brick (100mm) is rarely strong enough or waterproof enough for an external wall. You need at least a "double-brick" thickness to ensure the wall doesn't buckle under the roof's weight and to provide a buffer against driving rain.

Mykhailo · Answer

It really depends on the condition of the external wall and what finish you’re looking to achieve.

For most external rendering jobs, a total thickness of around 15–20mm is fairly standard. This is usually applied in two coats — a base coat (scratch coat) for strength and adhesion, followed by a top coat to level and finish the surface.

If the wall is uneven or has been previously damaged, you may need slightly more in certain areas to achieve a flat finish. The key is not just the thickness, but making sure it’s applied correctly and allowed to cure properly, especially given the British weather.

If you’re unsure, it’s always best to have the wall assessed on site, as external exposure and substrate condition can make a big difference.

Ken · Answer

It depends on what render, if its the cement and sand it is about 10mm and if it is the new style of render i.e K render etc the it would be about 6 mm.

Chris · Answer

Each coat approx 10mm .sand cement render  ,unless its the new polymere then can be 3mm .

Matthew · Answer

Minimum for single-coat render: Around 12.5 mm.
Minimum for double-coat render: Around 20 mm total.
Maximum per coat/layer: Avoid exceeding 25 mm in one go to prevent cracking, poor curing, or failure.
Thicker applications (e.g., over 25–30 mm) are possible on very uneven walls but should be built up in multiple coats with weaker mixes in subsequent layers.
Their are many different additives to add, all depending upon the surface which the rendering is to be applied too. Such as Fibres, SBR, PVA, Waterproofer, Plasticisers and Hydrated lime for some examples.

David · Answer

Render thickness typically ranges from 15mm to 25mm for traditional sand and cement, usually applied in two coats (a 10-15mm base coat and a 5-10mm top coat) to ensure proper weather protection.

How thick is render?

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