Description
At 1.5–2.0 mm application thickness with a 1.0 mm aggregate and BBA Certificate 13/5018, Atlas Cermit WN is the mineral wood-effect base render that anchors the Atlas concrete and wood-effect render range. A 25 kg bag covers 8–10 m² at 2.5–3.0 kg/m², offers high vapour permeability at μ 15/35, and accepts crisp silicone-stamp impressions while still wet, giving a true timber-board texture before the Bejca sealer system adds colour.
Where Atlas Cermit WN Performs Best on UK Projects
Atlas Cermit WN is the foundation layer of the Atlas wood-effect facade system — a polymer-modified, microfibre-reinforced cement-lime render formulated specifically to hold a sharp grain impression from a silicone wood stamp at 1.5–2.0 mm thickness. The 0.83 W/m·K thermal conductivity and μ 15/35 vapour permeability put it firmly in the mineral category, which matters on solid-wall retrofits and breathable EWI build-ups where a less permeable acrylic finish would trap moisture against the insulation layer.
The product earns its place on three project types: full wood-effect external facades over ATLAS ETICS or ATLAS ROKER EWI build-ups where mineral breathability and Euroclass A2-s1, d0 fire performance (within certified systems) are specification requirements; feature panels on porches, plinths, and entrance bays where the timber aesthetic is wanted as accent rather than full elevation; and interior feature walls in commercial reception areas, lobbies, and residential living spaces where the mineral, VOC-free composition is the safer choice over real timber cladding. The same bag works on Cermit-primed concrete, brick, EPS or mineral wool basecoats, gypsum render, and plasterboard.
Why Trade Specifiers Choose Atlas Cermit WN
- Sharp stamp impression at 1.0 mm aggregate: Fine fillers and microfibre reinforcement let the silicone wood stamp leave a clean, deep grain in the 1.5–2.0 mm wet layer — the difference between a convincing timber-board read and a vague texture.
- High mineral vapour permeability (μ 15/35): Moisture migrates out through the render rather than being trapped, which protects the underlying EWI or solid-wall build-up from interstitial condensation across the UK heating season.
- BBA Certificate 13/5018: Verified performance within ATLAS ETICS systems means specifiers can place Cermit WN inside a manufacturer-certified, BBA-listed build-up rather than as an out-of-system finish.
- Euroclass A2-s1, d0 (within system): Non-combustible classification within certified build-ups makes the render workable on buildings governed by the Building Safety Act, including taller residential blocks where combustible facade finishes are restricted.
- MYCO PROTECT alkalinity: The cement-lime binder's natural high pH inhibits algae, mould, and fungal growth — particularly useful on shaded north-facing elevations where biological colonisation tends to start first.
- Microfibre crack resistance: Embedded polymer fibres absorb the differential stresses caused by daily temperature swings on a facade, so the decorative grain stays intact rather than developing hairline fractures along the stamp lines.
Atlas Cermit WN — Data Sheet Highlights
| Parameter | Value |
|---|---|
| Pack size | 25 kg bag |
| Consumption | 2.5–3.0 kg/m² |
| Coverage per bag | ~8–10 m² |
| Layer thickness | 1.5–2.0 mm |
| Grain size | Up to 1.0 mm |
| Thermal conductivity (λ) | 0.83 W/m·K |
| Vapour permeability (μ) | 15/35 (high) |
| Reaction to fire | A2-s1, d0 (within certified system) |
| Pot life | ~60 minutes |
| Min curing before sealer | 3 days at +20 °C / 50% RH (5–7 days typical UK) |
| Application temperature | +5 °C to +25 °C |
| Primary substrate | Primed concrete, brick, EPS / MW basecoat, gypsum, plasterboard |
| Certification | BBA Certificate 13/5018 |
| System compatibility | ATLAS ETICS · ATLAS ROKER EWI |
How to Apply Atlas Cermit WN — Priming, Mixing, Stamping
Cermit WN goes on over a primed substrate that has had its suction equalised — usually with Atlas Base Coat Paint applied at the manufacturer's coverage rate and allowed to dry fully. Mix one 25 kg bag with clean water in a forced-action mixer to a smooth, lump-free consistency, let it stand for the slaking interval given on the bag, then re-stir briefly before trowelling onto the wall.
- Apply at 1.5–2.0 mm: Use a stainless steel trowel to lay the render and level it back to the grain (around the 1.0 mm aggregate). A 60-minute pot life means working in panel-sized sections that match what the team can stamp before the render firms up.
- Release agent on the stamp: Apply Atlas anti-adhesion agent to the silicone stamp before each impression — without it, the stamp tears the wet render surface and ruins the grain definition.
- Stamp while wet: Press the silicone wood stamp into the render before it skins over. Re-apply release agent between impressions to keep the grain crisp across the elevation.
- Cure before sealing: Allow 3 days at +20 °C and 50% RH as a minimum, or 5–7 days in typical UK ambient conditions of +8–15 °C, before applying the Bejca colour sealer. Sealing too early traps moisture and risks blistering.
For the full multi-product wood-effect method — covering primer, mixing, stamp technique, release agent timing, and sealer choice — read the concrete-effect render application method. The finished colour and weather-protection step is covered in the sealers for concrete-effect renders guide.
Installation Notes — Mixing, Pot Life, Section Planning
The 60-minute pot life governs how the day's work is broken down — stamp-capable sections should be sized so the last impression goes in well before that window closes, not at the edge of it. Two trowel-hands plus one dedicated stamper is the typical UK crew arrangement on facade panels above 20 m²; smaller crews work with smaller sections and accept slower overall progress for cleaner grain definition.
Mix water quantity is the most common cause of inconsistent stamp impressions. Too dry, and the stamp leaves shallow grain that the sealer cannot rescue; too wet, and the render slumps off the stamp when lifted, taking the grain with it. Follow the bag mixing ratio precisely and re-mix if the consistency drifts between sections.
Pro Tips From UK Installers Using Atlas Cermit WN
- Sample board before the facade: Stamp a 600 × 400 mm test panel of Cermit WN at 1.5 mm and at 2.0 mm to confirm which thickness gives the grain depth the client signed off — these two numbers produce visibly different finishes.
- Plan stamp sequence around joints: End each working day at a stamp line or external corner. A visible wet-edge mid-panel becomes a permanent shadow line once sealed, regardless of which Bejca colour goes on top.
- Release agent on every impression: Re-coat the stamp before each press, not every three. The polymer-modified render bonds to bare silicone faster than expected, particularly in warm weather.
- Cure 5–7 days in UK ambient: The TDS 3-day cure assumes lab conditions of +20 °C. UK ambient at +8–15 °C needs the longer interval before sealer, even when the surface looks dry to the touch.
- Always pair with a Bejca colour: Cermit WN as cured render alone is a chalky off-white that weathers unevenly. The Bejca silicone-resin sealer in teak, walnut, or birch is what locks the colour and adds the hydrophobic layer.
Is Atlas Cermit WN Right for Your Project?
- Right for wood-effect mineral facades: Authentic timber-board grain on full elevations, plinths, porches, and interior feature walls within ATLAS ETICS / ROKER BBA-certified systems where mineral breathability and A2-s1, d0 fire performance are specified.
- Coastal or high-exposure alternative: Atlas Silkon BA concrete-effect silicone render offers self-cleaning hydrophobic performance for coastal and high-pollution sites where mineral surfaces would require more frequent cleaning — at a higher material cost per m².
- Smooth concrete look instead of wood: Cermit WN can also be trowelled flat without the wood stamp for a clean industrial concrete-effect finish — a useful design pivot if the project moves away from the timber aesthetic.
- Need the colour-and-protection layer: Cured Cermit WN must be sealed with a Bejca colour finish — choose teak for a warm mid-tone, walnut for a deep dark grain, or birch for a pale Scandinavian wash.
FAQ — Atlas Cermit WN Coverage, Compatibility, Ordering
How much Cermit WN do I need for my project?
Each 25 kg bag covers 8–10 m² at 2.5–3.0 kg/m². For a standard 40 m² front elevation, plan for 5 bags of render plus primer, release agent, and two 4 L tins of Bejca sealer in the chosen colour. Adding one spare bag for projects above 30 m² keeps the wet edge live across stamp lines and absorbs natural variation in render thickness.
How long must Cermit WN cure before the Bejca sealer goes on?
Minimum 3 days at +20 °C and 50% relative humidity per the TDS, with 5–7 days recommended in typical UK ambient conditions of +8–15 °C. Sealing too early traps residual moisture behind the silicone-resin film, which can lead to uneven colour absorption or blistering in the first weather cycle. Check that the surface is dry to the touch and uniform in colour before sealing.
Can Cermit WN be used on internal feature walls?
The mineral, VOC-free composition makes Cermit WN suitable for interior gypsum render, plasterboard, and concrete substrates — useful for reception areas, restaurant interiors, and residential living rooms where a wood or concrete aesthetic is wanted without the fire or moisture concerns of real timber cladding. Prime the substrate first to equalise suction before applying the 1.5–2.0 mm decorative layer.
What does the full wood-effect system cost per square metre?
Material cost for the complete primer–render–sealer system typically lands between £6.50 and £8.50 per m², depending on coverage variation and wastage. That figure is well below real timber cladding cost per m² and significantly below high-end resin systems, while delivering A2-s1, d0 fire performance and a 5–12 year colour service life from the Bejca finish.
How often should I re-apply the release agent on the wood stamp?
Re-apply Atlas anti-adhesion agent before every stamp impression rather than every few presses. Polymer-modified mineral renders bond to bare silicone faster than installers expect, especially in warm conditions, and a single missed re-coat is usually what causes a torn grain on an otherwise clean panel.
Does the BBA certificate cover all uses of Cermit WN?
BBA Certificate 13/5018 covers Cermit WN as the render layer within ATLAS ETICS external wall insulation systems — the certification applies to the system as a whole, not the render as a standalone product. The A2-s1, d0 reaction-to-fire classification applies within those certified build-ups; for high-rise or Building Safety Act-governed projects, specify the full system rather than the render alone.