Description
Atlas Roker U Grey is the one cementitious mortar in the Renders World EPS adhesives basecoats range whose manufacturer sheet clears it for mineral wool slabs and polystyrene boards alike, bonding the insulation and forming the reinforced layer over it from the same bag.
Where Atlas Roker U Grey Bonds Best — Mixed Wool and EPS Elevations
Atlas Roker U Grey adhesive for wool and EPS 25kg bags bond mineral wool up to 30 cm thick and EPS up to 50 cm, so one product covers both board types on a mixed elevation. That dual scope is the reason it earns its place on a facade where the insulation specification changes part-way up the wall.
The manufacturer sheet lists it for both white and graphite EPS and for facade and lamella mineral wool, which covers every board format a UK retrofit is likely to present. The practical gain is procurement: one bag code, one mix ratio and one set of curing times across the whole scaffold.
- Mixed-board elevations where slabs from the mineral wool insulation range meet polystyrene on the same building, and switching adhesive mid-facade would mean two mixing stations.
- Solid-wall retrofit on Victorian and Edwardian brick, where the sheet permits bonding to sound, well-adhered paint films after an adhesion check on each substrate type.
- Graphite board work using the EPS insulation boards range, where the same mortar also serves as the reinforcing coat over the boards three days later.
Why Specifiers Choose One Adhesive Across Both Board Types
- Two board families, one bag: wool to 30 cm and EPS to 50 cm from a single 25 kg product, which removes the wrong-bucket risk that comes with running two adhesives on one lift.
- Declared adhesion of ≥ 0.25 MPa to concrete and ≥ 0.08 MPa to thermal insulation: the sheet states the insulation figure once, for thermal insulation generally, rather than separately for wool and EPS.
- Fibre-reinforced matrix: the sheet credits the fibres with raised resistance to micro-cracking at the initial setting stage and to cracking in service — the fibre-enhanced basecoat guide explains what that does to a reinforced layer.
- High vapour permeability, stated as a property: Atlas describes the mortar as not restricting water-vapour flow through the insulated wall, which matters most where mineral wool is doing the insulating. No Sd figure appears on the sheet, so none is quoted here.
- Named in Atlas system assessments: the sheet lists Roker U as a component of the ATLAS ETICS set under ITB-KOT-2020/1616 edition 1 and of ATLAS ROKER EPS under ITB-KOT-2020/1188 edition 1. Both are Polish national technical assessments — a point the adhesive selection guide puts in context against UK certification routes.
Atlas Roker U Technical Data — Declared Values and Their Scope
Every figure below is transcribed from the Atlas technical data sheet dated 19 February 2021, read in full this session. Where the sheet declares a value once for a whole class of substrate, it is published that way rather than split.
| Property | Declared value |
|---|---|
| Product type | Cementitious adhesive and reinforcing mortar |
| Pack size | 25 kg paper sack |
| Bulk density, dry mix | approx. 1.43 kg/dm³ |
| Mixing ratio | 0.22–0.24 l/kg — 5.50–6.00 l per 25 kg |
| Maturation time | approx. 5 minutes |
| Pot life | approx. 2 hours |
| Open time | min. 30 minutes |
| Application temperature | +5 °C to +30 °C, substrate and ambient |
| Reinforced layer, min/max thickness | 4 mm / 6 mm |
| Bonding — mineral wool | approx. 4.5–5.5 kg/m² |
| Bonding — EPS | 4.0–5.0 kg/m² |
| Reinforced layer — mineral wool | approx. 5.5–6.5 kg/m² |
| Reinforced layer — EPS | 3.0–3.5 kg/m² |
| Adhesion to concrete | ≥ 0.25 MPa |
| Adhesion to thermal insulation | ≥ 0.08 MPa |
| Compressive strength, PN-EN 1015-11 | Category CS IV |
| Water absorption after 24 hours | < 0.5 kg/m² |
| Max board thickness, wool / EPS | 30 cm / 50 cm |
| Shelf life | 12 months from production, dry storage |
| Soluble chromium (VI) | ≤ 0.0002 % |
The reinforced-layer thickness of 4–6 mm is declared once, for the layer itself, and is not split between wool and EPS on this sheet. The consumption rates are split, and the difference is large enough to change an order: a wool reinforced layer uses close to double the mortar an EPS one does.
How to Apply Roker U — Mixing, Bonding and the Reinforced Layer
Pour the sack into pre-measured water at 5.50–6.00 litres per 25 kg, mix with a slow-speed paddle to an even consistency, stand the mix for five minutes and remix. Use the mixed mortar within about two hours, and prime over-absorbent or unevenly absorbent substrates first — weak cement renders, aerated concrete and silicate blockwork are the ones the sheet names, and the substrate preparation guide covers the sequence.
Bonding EPS boards
Apply the mortar to the board, never to the wall, as a perimeter bead at least 3 cm wide plus 6–8 dabs of at least 8 cm diameter. Aim for coverage of at least 40 % of the board face, rising to a minimum of 60 % once the board is beaten in, and keep the bed under 10 mm thick. On flat, true substrates the sheet allows a full-face pass with a 10 × 10 mm notched trowel instead.
Bonding mineral wool slabs
Wool takes two passes. Skim the slab face thinly first to key the fibres, then lay the working bed over that skim and comb it with a 10 × 10 mm notched trowel before setting the slab to a staggered joint pattern. Leave mechanical fixings until at least 24 hours after bonding.
Building the reinforced layer
Start the reinforced layer no earlier than three days after the boards go on. Over wool, lay two-thirds of the final quantity, bed the fibreglass mesh into it, then close with the remaining third; over EPS the sheet allows a single operation with a 6–10 mm notched trowel. Lap the mesh a minimum of 10 cm and set 20 × 35 cm diagonal patches at 45° into the corners of every opening before the main mesh goes over them — the reinforcement layer guide covers lapping discipline in detail.
Installation Conditions, Curing Times and Fixing Density
Work between +5 °C and +30 °C on both substrate and air, keep scaffold sheeting up, and stop for rain, snow or strong wind. Rendering follows about three days after the reinforced layer, once the render manufacturer's own conditions are also satisfied.
- Fixings: a minimum of 4 per m², with the actual count set by the insulation technical design — the fixing pattern and spacing guide owns the layout question.
- Pin material: wool takes galvanised metal-pin anchors; EPS accepts plastic or steel pins. This is a sheet requirement, not a preference, and it is the detail most often missed on a mixed elevation.
- Graphite EPS: keep the boards shaded and cool through bonding and initial set. Warm graphite board is the one condition the sheet flags for adhesion, and shading solves it outright.
- Doubtful substrates: bond 10 × 10 × 10 cm EPS cubes as a pull test, reading them at three days, or at five days below 10 °C and above 80 % humidity. A cube that tears through the foam confirms the wall is sound.
Reaction to Fire — Which Class Belongs to Which Finish
The sheet declares reaction to fire for the finished ATLAS ROKER system, not for the mortar in the bag, and the class changes with the render on top. Read the row that matches the finish actually specified.
| System as tested | Declared class |
|---|---|
| ATLAS ROKER system with acrylic and silicone renders | B-s1,d0 |
| ATLAS ROKER system with mineral and silicate renders | A2-s2,d0 |
A thin-coat silicone finish therefore sits in the B-s1,d0 row, whatever the insulation beneath it is, and neither class transfers to a build-up assembled from other components. Height limits, building class and the project fire strategy are separate questions under current UK guidance, and the facade fire requirements guide is the page that works through them.
Choosing Between Roker U and the Hoter U Adhesives
All three products bond insulation and take mesh at the same stage of the build-up, so the choice comes down to the board on the wall and the shade of the finish above it.
| Product | Board scope on its own sheet | Choose it when |
|---|---|---|
| Atlas Roker U Grey | Mineral wool to 30 cm and EPS to 50 cm | Wool is on the wall, alone or alongside EPS |
| Atlas Hoter U Grey | Read from its own sheet | EPS-only elevations, grey mortar under mid or deep shades |
| Atlas Hoter U White | Read from its own sheet | EPS-only elevations finished in pale or white render |
Both Hoter U products sit in the same collection as this one and their scopes are stated on their own data sheets rather than borrowed from this page. Where the board decision itself is still open, the wool against polystyrene comparison weighs the two materials on the criteria that actually move a specification.
Is Roker U Right for Your Build-Up?
- Wool anywhere on the elevation — Roker U is the mortar in this range whose sheet covers it, and the two-pass skim method is what makes that scope work on site.
- Mixed wool and EPS — one product, one mix ratio, one curing programme, sized against the wool zones because they consume the most.
- EPS-only, cost-led jobs — an EPS-specific adhesive may work out keener per square metre, so compare the sheets before committing a large order.
- Whole-system context — the EWI build-up guide shows where the bonding and reinforcing layers sit relative to everything else on the wall.
Renders World lists Roker U Grey adhesive for wool and EPS 25kg at £13.80 per 25 kg bag, August 2026, showing as available at that fetch. That is £13.80 ÷ 25 kg = £0.552 per kg, so a wool bond-and-reinforce build-up at 10.0–12.0 kg/m² runs £5.52–£6.62/m² in adhesive, and an EPS one at 7.0–8.5 kg/m² runs £3.86–£4.69/m². Add the boards from the ranges above and the order is complete in one basket.
FAQ — Roker U Coverage, Compatibility and Specification
How many bags cover 100 m²?
Price the zones separately. Wool needs 4.5–5.5 kg/m² to bond plus 5.5–6.5 kg/m² to reinforce, so 10.0–12.0 kg/m² × 100 m² = 1,000–1,200 kg ÷ 25 = 40–48 bags, or 44–53 with 10 % waste. EPS needs 4.0–5.0 plus 3.0–3.5, so 7.0–8.5 kg/m² × 100 m² = 700–850 kg ÷ 25 = 28–34 bags, or 31–38 with waste.
Can one bag code serve both board types on the same wall?
Yes — that is the scope the data sheet declares, covering white and graphite EPS and both facade and lamella wool. The application method still changes by board: wool takes the skim-and-bed pass, EPS takes bead-and-dabs.
What does this do that an EPS-only adhesive does not?
It carries a declared bond to mineral wool, which an EPS-specific mortar does not, and it is formulated for the vapour flow a wool build-up depends on. On an all-EPS job that extra scope buys nothing, so the EPS-specific products are worth pricing.
What weather limits apply during application?
Substrate and air both need to sit between +5 °C and +30 °C, with sheeting on the scaffold and no work through rain, snow or strong wind. Graphite boards want shade through bonding and initial set, which is easily managed with the sheeting already up.
Does the declared fire class make a wall compliant?
The classes belong to the tested ATLAS ROKER system with a named render family, so they describe an assembly rather than the bag. UK compliance rests on the project fire strategy and the building's height and use class, assessed for the specific build-up being installed.
Written by Mariusz Saja. Technically reviewed by Rafał Wyrzykowski. Last reviewed Aug 2026.
Technical Documentation — Atlas Roker U Data Sheet