ATLAS CERMIT WN SMOOTH RENDER 25KG

Atlas Cermit WN is the mineral render behind the wood-grain facades in the wood and concrete-effect finishes range. It is a white cement-lime render that goes on at about 4 mm and is then pressed with a silicone form, so the grain is impressed into the wet coat rather than floated into it. The interval between trowel and form is what decides how the wall ends up looking.

Where Atlas Cermit WN Sits in the Build-Up

The sheet gives Cermit WN two positions on a facade:

• as the finishing coat of an external wall insulation system, over EPS boards and over mineral wool;
• directly on flat, prepared mineral backgrounds — concrete and traditional cement and cement-lime plasters, once seasoned and primed.

The sheet keeps Atlas Cermit WN to facades. It is not laid on ceiling soffits, and not on walls inside a building, on gypsum plaster or on plasterboard.

Which Buildings It Is Meant For

Projects fall into two columns, and the split is finer than commercial against industrial. Industrial construction sits on the suitable side for Cermit WN; industrial warehouses do not.

Project type	Position on the sheet
Housing, offices, schools, health buildings	Suitable
Retail and service buildings	Suitable
Industrial construction	Suitable
Passive and energy-efficient construction	Suitable
Industrial warehouses and transport structures	Silicone render instead
Farm and livestock buildings	Silicone render instead
Heritage buildings	Silicone render instead

 

Exposure is the second axis, and every category is marked suitable: urban, industrial, rural, damp ground near water, sites among trees and greenery, and shaded elevations. Two declared properties carry that — pH 12 and a water repellent in the mix, tied on the sheet to natural resistance against mould fungi and algae.

Declared Specification

Parameter	Declared value
Composition	White cement, lime, dolomite aggregates, water repellent
Maximum aggregate	up to 1.0 mm
Layer thickness	approx. 4 mm
Consumption	approx. 2.5 to 3.0 kg per square metre
Water	0.21 to 0.24 l per kg, so 5.25 to 6.0 l per bag
Rest, then remix	5 minutes
Working time	approx. 1.0 hour
Before the form goes in	approx. 20 to 60 minutes
Hard to the touch	after 24 hours
Ready for the Bejca stain	after 3 days at +20 °C, 50% humidity
Working temperature	+5 °C to +30 °C, substrate and air
Reaction to fire	class A1 to PN-EN 998-1:2016
Declaration of performance	108/1/CPR
Water absorption	class Wc1
Water permeability	1 ml/cm² or less after 48 h
Adhesion	0.3 N/mm², fracture pattern FP:B
Water vapour permeability	μ of 30 or less
Diffusion-equivalent air layer	Sd of 0.14 m to 1.4 m, category V2
pH of the mortar	12, which is the high-alkalinity figure
Silicone form	2 m × 0.2 m
Packaging	25 kg paper bag, the only pack made
Shelf life	12 months from the production date

 

Vapour permeability appears twice because the two figures answer different questions. The μ value belongs to Atlas Cermit WN as a mortar. The Sd range and its V2 category describe the finished surface with the stain on it, and that is the figure a breathability calculation for the wall needs.

Mixing and Laying Atlas Cermit WN

1. Dry-mix the bag contents, then pour into 5.25 to 6.0 l of water per 25 kg and mix mechanically to a uniform mass.
2. Leave it 5 minutes and remix. Use the batch within about an hour, stirring occasionally and adding no more water.
3. Lay Atlas Cermit WN on at about 4 mm, comb it through with a 10 mm notched trowel to equalise the layer, then smooth it back.
4. Grease the 2 m × 0.2 m silicone mould thoroughly with the Atlas anti-adhesive agent before use, and keep its recesses clear.
5. Press the grain once the surface has stiffened and surface-dried — 20 to 60 minutes, weather dependent. Work wet on wet and plan breaks at corners and downpipes.
6. Wash the mould with water and detergent afterwards. A mould left unwashed ends up permanently deformed.

The coat is hard after 24 hours and takes the Bejca tinted impregnant after 3 days at +20 °C and 50% humidity. Cooler British weather stretches both figures. Mould technique for the pattern itself is covered in the guide to wood and brick stencils for render.

Substrate Seasoning and the Key Coat

Substrate	Seasoning	Key coat
Reinforced ETICS layer in Stopter K-50	min. 3 days	None required
Reinforced ETICS layer in other Atlas mortars	min. 3 days	Cerplast key coat
New cement and cement-lime plasters	min. 7 days, moisture 4%	Cerplast key coat
Concrete backgrounds	min. 28 days, moisture under 4%	Cerplast key coat

 

Those periods assume +20 °C and 50% humidity, so a cold spring extends them. One row is worth planning around: a reinforced layer built in Stopter K-50 takes this render with no key coat at all, while every other background needs a Cerplast quartz key coat first — Renders World holds it in 25 kg and 15 kg.

How Many Bags for the Elevation

• At 3.0 kg/m², a 25 kg bag covers 25 ÷ 3.0 = 8.3 m².
• At 2.5 kg/m², the same bag covers 25 ÷ 2.5 = 10 m².

The rate is fixed by a trial on the actual substrate, and a 4 mm layer points at the heavy end of the range, so order against 8.3 m² per bag and keep a margin. Renders World holds Atlas Cermit WN in the 25 kg bag, and the form, the release agent and the Bejca tinted impregnant sit on the same shelf, so the whole finish can be ordered together.

What the Sheet Does Not Cover

Question	What is on record
Thermal conductivity	Not declared for this render, so no λ figure is quoted
BBA Agrément 13/5018	Issued to systems; Cermit WN is not named in it
Wall fire performance	Class A1 is declared for the mortar, not for a finished wall

 

What the render does carry is European Technical Assessment ETA 06/0173, plus two Polish ITB national assessments held at system level for the Atlas ETICS and Atlas Roker systems. A UK specifier reads those as evidence about the system, and confirms wall performance with the system holder against current Approved Document B guidance.

Atlas Cermit WN: Quantities, Compatibility and Conditions

What goes under it and what goes over it?

Underneath: a Cerplast key coat on concrete, on cement plasters and on reinforced layers built with Atlas mortars other than Stopter K-50, which needs none. Over the top: the Bejca tinted impregnant after three days, which is what colours the grain.

What weather does it allow?

Substrate and surroundings between +5 °C and +30 °C, with fresh work protected from direct sun, wind and rain while it goes on and while it dries. The 24-hour and 3-day figures assume +20 °C and 50% humidity.

Does it need a key coat over insulation board?

Only sometimes. A reinforced layer built in Stopter K-50 takes the render after three days with no key coat; a reinforced layer built in any other Atlas mortar needs a Cerplast key coat first, and so do concrete and cement plasters.

Is the silicone form reusable?

Yes. Renders World treats it as the part of the kit worth protecting.

• Grease it with the anti-adhesive agent before every impression.
• Clear render out of the recesses as you work.
• Wash it with water and detergent at the end of the session. A mould left unwashed deforms permanently.