Description
Atlas Silicone-Silicate Render 25kg is the silicone finish Renders World supplies where a wall has to stay open to water vapour and the specification has to be evidenced on paper as well as on site. It is a ready-to-use paste, tinted to order in our own plant, and it goes on solid-wall and insulated elevations alike.
Where Atlas Silicone-Silicate Render 25kg Fits on Solid-Wall and Heritage Projects
Two documents govern this finish, and they answer different questions. The Atlas product data sheet, updated 10 February 2026, declares what the material itself does. BBA Agrément Certificate 13/5018 names it as a finishing coat of the Atlas/Aval EPS external wall insulation system and sets what that system is certified for. Quote the sheet for the material and the certificate for the build-up, and a specification holds together.
Within the silicone render range it is the finish chosen where vapour openness is the governing requirement. The certificate scopes it as follows.
- Certified substrates, at system scope: masonry, normal-weight concrete, lightweight concrete, autoclaved concrete and no-fines concrete, on new or existing buildings, with or without existing render.
- Existing walls: the certificate expects the system to go on where the inner surface shows no dampness other than condensation, so a five-minute internal check before ordering keeps the specification sound.
- Position in the build-up: a ready-to-use paste over the Atlas Silkon ANX key coat, which is what the certificate ties it to.
For the conservation route — consent, substrate compatibility and what a conservation officer will want to see — the heritage and conservation render guide works through the specification path.
Declared Performance — What the Atlas Data Sheet States
Every value below comes from the Atlas product data sheet, dated 10 February 2026 and linked at the foot of the page. The scope is the material in the bucket, not a wall build-up.
| Property | Declared value | Scope |
|---|---|---|
| Water vapour permeability | V1 (high) | Material, EN 15824 |
| Vapour diffusion resistance | Sd below 0.14 m | Material, EN 15824 |
| Water absorption | W2 (medium) | Material, EN 15824 |
| Adhesion | 0.35 MPa | Material, EN 15824 |
| Reaction to fire | A2-s1, d0 | Material, not a construction |
| Declaration of Performance | 125/3/CPR | Material, EN 15824:2017 |
| Consumption, 1.5 mm by hand | From 2.2 kg/m² | Material, per coat |
| Consumption, 1.5 mm by machine | From 1.9 kg/m² | Material, per coat |
| Consumption, 2.0 mm by hand | From 2.8 kg/m² | Material, per coat |
| Substrate and air temperature | +5 to +30 °C | Material, work and curing |
| Shelf life | 12 months | Material, unopened |
| Colour range | 406 SAH shades | Manufacturer tinting range |
Three of those rows are why a specifier reaches for Atlas Silicone-Silicate Render 25kg rather than a straight silicone finish. V1 is the open end of the EN 15824 vapour scale, and this is the only Atlas paste finish in the Renders World range declared at V1 — the silicone, acrylic and Gemini RS finishes are all declared V2. On a solid wall or a lime-backed elevation, that single row is usually the argument. Sd below 0.14 m is the threshold that defines V1, so the two rows are one fact stated twice, in the form a specification and a condensation risk analysis each ask for.
The third is A2-s1, d0, declared for the material and not for a wall. It is the highest reaction-to-fire class a paste finish of this type carries, and the scope matters: A2-s1, d0 is the material's own class. Whether a whole wall construction is classified is a separate question, and the certificate answers that one.
Why Specifiers Choose a Silicate Hybrid on a Certified Build-Up
Alongside the vapour figures, the commercial case is predictability. Each point here comes straight off the certificate, which is what makes them usable in a submission. So does the installer route: the system is installed by contractors trained and registered by the certificate holder, and that is the evidence trail warranty providers and Building Control ask for.
- The tightest coverage band in the Atlas finishing range: 2.5 to 3.0 kg/m² inside the certified build-up, against 2.5 to 5.5 kg/m² for the silicate and acrylic-silicone finishes, so material take-off on a large elevation lands within a much narrower window.
- A key coat that is fixed, not chosen: Silkon ANX at 0.25 to 0.35 kg/m² is the key coat named for this silicone render, which removes the most common ordering error on a mixed-brand facade.
- Thirty-year certified system life: under normal service conditions, installed and maintained to the certificate, the system is assessed as remaining effective for at least 30 years.
What BBA 13/5018 Records for the System Around It
| Property | Certified value and scope |
|---|---|
| Product form | Ready-to-use silicone-silicate paste |
| Particle grain sizes | 1.5 to 2.0 mm |
| Coverage in the system | 2.5 to 3.0 kg/m² as a finishing coat |
| Coverage per bucket | About 8.3 to 10 m² per 25 kg |
| Named key coat | Silkon ANX at 0.25 to 0.35 kg/m² |
| Reinforcing mesh | Atlas 150, 150 g/m², 4.5 by 5.0 mm |
| Basecoat thickness | 2.0 to 5.0 mm, or 4.0 to 6.0 mm twin mesh |
| Height limit, England, Wales, NI | No storey more than 18 m above ground |
| Height limit, Scotland | No storey at 11 m or more, or within 1 m of a boundary |
| Certificate | BBA 13/5018, Sheet 1, fourth issue 2022 |
| Fire class of a construction using it | No classified construction names it |
The last row catches people out, so it is worth being plain about. The certificate's reaction-to-fire table classifies complete constructions, and the rows in it name Atlas Cermit Mineral, Atlas Silicate Render, Atlas Silicone Render and Atlas Acrylic-Silicone Render as the finishing coat. None of those rows names it. Its own A2-s1, d0 from the data sheet therefore stands as a material class and nothing more, and no construction class is carried across to it from a neighbouring row. The same applies to the impact Use Category table, where the row identity could not be resolved cleanly enough to publish. Where a project brief calls for a classified construction, the fire strategy has to name the whole build-up, and the designer settles it.
How to Apply the Render Over a Reinforced Basecoat
The material is supplied ready to use, so there is no mixing ratio and no pot life to manage — stir each bucket to a uniform consistency with a slow-speed paddle and keep the batch sequence consistent across an elevation. Lay on to a coat thickness matching the grain with a stainless float, then texture with a plastic float while the surface is still workable. The layers underneath are where the certified figures matter most.
- Adhesive and boards: cementitious powder adhesive at 4.0 to 5.0 kg/m², covering a minimum of 40% of the board, with supplementary mechanical fixings placed while the adhesive is setting.
- Reinforced basecoat: 2.0 to 5.0 mm thick with Atlas 150 alkali-resistant mesh embedded and trowelled smooth, increasing to 4.0 to 6.0 mm where a second mesh layer is specified.
- Key coat: Silkon ANX at 0.25 to 0.35 kg/m² once the basecoat is dry; the wider exterior render primers range covers the consolidating products used first on high-suction substrates.
Work wet-on-wet across a whole elevation and plan breaks at corners, downpipes or colour changes so joints fall where the eye expects them. The EWI system build-up guide sets out the full layer sequence, and the step-by-step thin coat render method covers the trowel work in detail.
Installing Silicone-Silicate Render in UK Conditions
The Atlas sheet gives a working range of +5 to +30 °C for substrate and air alike, and that range covers curing, not only the hour the material goes on. A UK booking is therefore made against the wall temperature first thing and the overnight forecast. Protecting the elevation from direct sun, wind and driving rain while the coat cures gives the most uniform finish, and unopened buckets carry 12 months from production, so on a phased contract order the later elevations later rather than storing a whole job from day one.
- Check the wall, not the forecast: substrate temperature on a shaded north elevation lags air temperature by a wide margin first thing, and an infrared thermometer settles it in seconds.
- Watch the ceiling as well as the floor: +30 °C is the declared upper limit, and a south-facing wall in direct sun reaches it on a day the air never does.
- Prepare and prime to the substrate: the substrate preparation guide covers suction testing and consolidation on old lime plaster and aerated block, and the seasonal application timing guide maps the UK calendar month by month.
How the Atlas Finishing Coats Compare in One Certified System
All three finishes below are named in the same certificate, at the same stage of the same build-up, which makes the comparison a like-for-like one. Two columns change a decision: the vapour class, because it decides whether the wall can dry outwards, and the key coat, because it changes what else goes on the order.
| Finishing coat | Vapour class | Grain sizes | Coverage in system | Key coat named |
|---|---|---|---|---|
| Silicone-silicate | V1 (high) | 1.5 to 2.0 mm | 2.5 to 3.0 kg/m² | Silkon ANX |
| Silicone | V2 (medium) | 1.5 to 2.0 mm | 2.5 to 3.5 kg/m² | Silkon ANX |
| Acrylic | V2 (medium) | 1.5 to 3.0 mm | 2.5 to 5.0 kg/m² | Cerplast |
The silicate hybrid is the only one of the three declared at V1, and it carries the narrowest consumption band, so quantity risk on a large contract is lowest here. The acrylic shares its key coat with the mineral and acrylic-silicone finishes, which is worth knowing if a facade is being finished in more than one material.
Choosing Between This Finish and the Rest of the Range
- Choose Atlas Silicone-Silicate Render 25kg where the wall has to dry outwards — solid masonry, lime-backed or heritage fabric — or where the specification is an Atlas EPS build-up inside the certificate's storey-height limits and you want the tightest coverage band for take-off purposes.
- Choose a straight silicone finish where the project is standard modern masonry and V2 is sufficient for the wall; the parent collection lists the white and grey bases side by side.
- Settle the colour first — shade and grain both change how a facade reads, and the render colour charts and catalogues let you sign a physical swatch off before the tinting run.
At the Atlas sheet's 2.2 kg/m² for a 1.5 mm layer laid by hand, one bucket covers about 11 m². Inside the certified build-up, where the rate runs 2.5 to 3.0 kg/m², the same bucket covers 8.3 to 10 m². Prices are not published here because they move; ask and you get the current figure against the shade, the grain and the quantity.
Renders World tints to order on its own equipment and processes orders the same day where the stock is there. Delivery is quoted after the order rather than calculated at checkout, and the terms sit in the shipping policy. A tinted bucket is mixed for you and sits outside the 14-day change-of-mind return — that is set out in the cancellations and returns policy. Collection is open too: the counter at Unit 9A, Central Trading Estate in Southampton runs Monday to Friday from 7am to 5pm and Saturday morning until noon, and a bucket is tinted to your shade there and then.
FAQ — Coverage, Certification and Heritage Use
How many buckets does a 100 m² elevation take?
That depends on which rate the job is ordered against, and the two rates answer two different questions. Work it through:
- Data sheet, 1.5 mm by hand: 100 m² × 2.2 kg/m² = 220 kg; 220 ÷ 25 = nine buckets, plus a tenth for reveals, cut-outs and detailing.
- Certified build-up: 100 m² × 2.5 kg/m² = 250 kg and 100 m² × 3.0 kg/m² = 300 kg; that is ten to twelve buckets, plus about ten per cent, so eleven to fourteen.
- Machine application at 1.9 kg/m² pulls the sheet figure down to 190 kg, or eight buckets before the allowance.
Order against the certified band if the job is a certified EWI build-up, and against the sheet if it is not. The render coverage calculator runs the same arithmetic across other grains and products.
What else does the certified build-up need?
Silkon ANX key coat at 0.25 to 0.35 kg/m² directly beneath it, over a reinforced basecoat of 2.0 to 5.0 mm carrying Atlas 150 mesh at 150 g/m². Swapping the key coat for a different one takes the wall outside the certified specification, so order the two together.
What vapour figures can I put in a condensation risk analysis?
V1 to EN 15824, with an Sd value below 0.14 m, both declared for Atlas Silicone-Silicate Render 25kg on the Atlas sheet and both covered by Declaration of Performance 125/3/CPR. That is the figure a hygrothermal calculation needs, and it is the open end of the scale rather than a mid-range one. The classes are declared for the paste alone; the rest of the build-up carries its own resistances and they add up, so run the whole section rather than the topcoat.
What does BBA 13/5018 actually certify?
The Atlas/Aval EPS external wall insulation system as a whole, not this bucket on its own. Certificate limits apply to the system. In England, Wales and Northern Ireland it should not be used on buildings with a storey more than 18 m above ground level. In Scotland it should not be used on buildings with a storey 11 m or more above ground level, or within 1 m of a boundary. The material's own A2-s1, d0 does not lift those limits, and the project fire strategy should confirm the specification.
How does it differ from the plain Atlas silicone render?
On the two Atlas sheets, in the vapour class above all: V1 here against V2 for the plain silicone finish, with adhesion equal at 0.35 MPa on both. The binder is the reason — potassium silicate alongside the silicone resin — and on a wall that has to breathe it is the difference that decides the specification.
Is it the right choice for a listed building?
It is the strongest candidate in this range on the vapour figures, and V1 with an Sd below 0.14 m is what a conservation officer or a building surveyor will ask to see. Two cautions stand. The certificate covers it as part of an insulated system rather than as a coating for solid heritage fabric, so on a bare historic wall the specification rests on the data sheet alone. And consent comes first: agree the finish with the conservation officer against both documents before any material is ordered or tinted, because a tinted batch is made for the job.
Technical Documentation — Data Sheet and Agrément Certificate