Description
A crack-free basecoat that survives decades of thermal cycling starts with the right fibre-reinforced mortar, and Atlas Hoter U Grey is the 2-in-1 cement adhesive and basecoat that bonds EPS and XPS boards and embeds fibreglass mesh from one 25 kg bag — delivering ≥0.25 MPa adhesion to concrete with an extended 4-hour pot life that keeps big basecoat runs moving.
Where Atlas Hoter U Grey Performs Best — UK EPS and XPS Walls
Atlas Hoter U Grey is a fibre-reinforced 2-in-1 cement mortar that bonds EPS and XPS boards at 4.0–5.0 kg/m² and forms the mesh-reinforced basecoat at 3.0–3.5 kg/m², certified under EN 15824:2017 for UK EWI systems. Sold within the EPS adhesives and basecoats range at Renders World, one bag code covers both the bonding and reinforcement stages on a typical 100 m² elevation, simplifying procurement and cutting stock-keeping on the gantry. Structural microfibres distribute thermal and mechanical stress across the cured layer, holding the basecoat together against hairline cracking from solar gain and substrate movement.
The grey-cement formulation suits projects where the decorative coat is a mid- or dark-tone silicone or acrylic render, since light show-through under the finish is not a concern. On standard and graphite EPS facades, extruded polystyrene plinth zones, and mineral-substrate solid-wall retrofits over brick or block, it is the workhorse mortar UK specifiers reach for — installers consistently report the 4-hour pot life is what changes the working day on larger elevations. The full board-type-to-mortar decision matrix sits in the EPS adhesive selection guide.
Why Trade Specifiers Choose Atlas Hoter U Grey
- One product, two stages: Bonds insulation boards and embeds fibreglass mesh in the reinforced basecoat, so a single 25 kg bag code covers both site operations and reduces stock-keeping on the scaffold.
- 3D microfibre crack control: Structural microfibres distribute thermal and mechanical stress across the cured layer, holding the basecoat together against hairline cracking from solar gain and substrate movement on tall elevations.
- 4-hour pot life at 20 °C: Mixed mortar stays workable for around four hours, so a two-person team mixes bigger batches and applies long stretches of basecoat without restarting at the mixer every 90 minutes.
- ≥0.25 MPa adhesion to concrete: Tested bond strength on dense substrates supports certified Atlas ETICS detailing on jobs where Building Control and warranty providers verify the specification.
- Highly vapour permeable: The cured mortar breathes with the wall, letting interstitial moisture escape rather than building up behind a sealed insulation layer.
- EPS, graphite EPS, and XPS in one spec: Compatible with all three polystyrene grades, so the same adhesive bonds the field boards and the perimeter XPS plinth strip on a single elevation.
- BBA and NSAI certified system component: Documented within the Atlas ETICS family, giving developers and Building Control the certification trail required for warranty sign-off on UK facades.
Technical Specifications — Atlas Hoter U Grey Data Sheet Highlights
| Property | Value |
|---|---|
| Product type | Cement-based 2-in-1 adhesive and reinforcing mortar |
| Composition | Grey cement, mineral fillers, polymer modifiers, microfibres |
| Pack size | 25 kg bag |
| Mixing ratio | 5.0–5.5 l clean water per 25 kg |
| Pot life | ~4 hours at 20 °C |
| Open time | Min. 25 minutes |
| Application temperature | +5 °C to +25 °C (substrate and ambient) |
| Consumption — board fixing | 4.0–5.0 kg/m² (≈5 m² per bag) |
| Consumption — basecoat and mesh | 3.0–3.5 kg/m² (≈7 m² per bag) |
| Reinforced layer thickness | 2–5 mm |
| Adhesion to concrete | ≥0.25 MPa |
| Board thickness supported | EPS up to 500 mm; XPS up to 200 mm |
| Standards / certification | EN 15824:2017 · BBA · NSAI · ETA within Atlas ETICS |
| Application method | Hand trowel or rendering machine |
| Shelf life | 12 months (sealed, dry storage) |
| Manufacturer | Atlas Sp. z o.o. |
How to Apply Atlas Hoter U Grey — Mixing Ratio, Pot Life, and Coverage
Mix the 25 kg bag into 5.0–5.5 litres of cool, clean water — powder into water — with a paddle mixer on low speed until lump-free, rest five minutes, then remix briefly to activate the polymers. Apply between +5 °C and +25 °C on clean, sound substrates. For board fixing, lay a 3–4 cm perimeter band with three to six central dots, then press each board until contact covers at least 40 % of the rear face, the figure the certified Atlas ETICS detail requires. On dense concrete the mortar bonds directly; on absorbent or dusting substrates such as aerated block or old lime render, a pass of Atlas Uni-Grunt evens out suction first.
After the bonding layer cures at roughly 24 hours and mechanical fixings are in, trowel a 2–3 mm continuous basecoat, press Atlas 150 g/m² fibreglass mesh into the wet mortar with minimum 100 mm overlaps, then smooth a second thin pass so the mesh sits in the outer third of the layer. Work in shade or overcast conditions where possible, since direct midday sun on dark graphite EPS can flash-dry the thin layer before the mesh beds in. The basecoat and mesh reinforcement guide covers overlap discipline, corner detailing, and the diagonal patches around openings.
Installation Notes — Conditions, Mechanical Fixings, and Finishing
Keep both substrate and ambient temperature between +5 °C and +25 °C for at least 24 hours after application. Mechanical fixings are mandatory on certified ETICS regardless of adhesive grade — install them through the boards after the bonding layer has fully cured, typically at 6–8 per m² for the wind-load zone, then encapsulate the anchor heads within the reinforced basecoat. Confirm board-face temperature with an infrared thermometer rather than the air reading, because dark graphite EPS warms faster than masonry and can exceed the working window on a sunny scaffold.
Allow the finished basecoat a minimum of three days to cure before priming and the decorative render, extending that in cool or humid weather so the surface is fully ready for the quartz primer. On a full Atlas build-up, Hoter U Grey (board fixing) → mechanical fixings → Hoter U Grey (mesh basecoat) → quartz primer → a certified Atlas thin-coat silicone render completes the facade, keeping every layer inside one warranted system. Clean tools with water before the mortar sets; store sealed bags off the ground under cover.
Pro Tips From UK Installers Using Atlas Hoter U Grey
Experienced installers rely on a handful of habits to turn the long pot life and fibre reinforcement into a faster, cleaner basecoat run — the reward is fewer mixer restarts and no mesh telegraphing through the finish.
- Mix to the workboat, not the bag: Two-thirds of a bag in one bucket gives a stiffer first mix that thins predictably with the remaining water, easier to control than chasing consistency from a full bag.
- Use the long pot life as a logistics tool: On 200 m² and above, mix a full station batch at the start of a run — the four-hour window lets one operative trowel continuously while another preps the next bay.
- Watch the wet edge, not the clock: The 25-minute open time governs how long you have to embed mesh; losing the wet edge is the most common cause of mesh telegraphing through the finish render.
- Tape the perimeter before basecoating: A clean masking line along reveals and verges saves twenty minutes of trowel correction later and keeps the bead nose crisp.
- Shade the dark boards: On graphite EPS in summer, sequence basecoat work to follow the shade around the building so the mortar never skins before the mesh is in.
How Atlas Hoter U Grey Compares to the White Variant and Sibling Adhesives
Hoter U comes in grey and white cement on the same fibre-reinforced base, and Renders World stocks a universal wool-and-EPS alternative for mixed-board buildings. The table sets the three against each other so the choice follows the topcoat colour and board type on your elevation.
| Variant | Key Spec | When to Choose |
|---|---|---|
| Atlas Hoter U Grey 25 kg | Grey cement · fibre-reinforced · ≥0.25 MPa | Mid and dark topcoats, standard EWI |
| Atlas Hoter U White 25 kg | White cement · same fibre reinforcement | Light and pastel topcoats, no show-through |
| Roker U Grey 25 kg | Universal · mineral wool + EPS rated | Mixed wool/EPS buildings, one adhesive |
Is Atlas Hoter U Grey Right for Your Project?
- Yes — for EPS, graphite EPS, or XPS EWI under a mid or dark topcoat: One certified adhesive and basecoat across the elevation, with a long working time that suits batch mixing on larger jobs and full Atlas ETICS documentation for warranty sign-off.
- Going under a light or pastel finish? The white-cement GRP sibling Atlas Hoter U White 25 kg offers identical fibre-reinforced performance with no grey show-through, reducing the need for a tinted primer under pale silicone renders.
- Insulating with mineral wool? Mineral wool needs a more vapour-permeable adhesive engineered for the slab structure — Roker U Grey 25 kg is the wool-and-EPS-rated alternative in the same range, keeping the A1 fire layer inside its certification envelope.
- For full-system specification, pair it with the EPS insulation boards range as the thermal layer, then a quartz primer and a certified Atlas thin-coat render — staying inside one ecosystem protects warranty cover on the finished facade.
FAQ — Atlas Hoter U Grey Coverage, Compatibility, and Ordering
How many bags of Atlas Hoter U Grey do I need per 100 m² of EWI?
At average rates of 4.5 kg/m² for board fixing and 3.5 kg/m² for the basecoat, a 100 m² elevation consumes about 450 kg + 350 kg = 800 kg of mortar, or 32 bags. Order 35 bags per 100 m² to absorb the 10 % wastage that comes with uneven substrates, complex window detailing, and offcut losses on long basecoat runs. As a 2-in-1 product it covers both stages, so there is no separate adhesive and basecoat order to reconcile.
How long does the mixed mortar stay workable in the bucket?
At a standard 20 °C the mixed paste stays workable for approximately four hours, roughly double the working time of conventional 90-minute adhesives. Plan batch sizes around that window — a two-person team can comfortably mix 50 kg at a time on warm summer days and still finish the bucket before it stiffens. Above +25 °C the window shortens, so shading the bucket and mixing to demand preserves the workability the product is valued for.
Can I use Atlas Hoter U Grey to bond mineral wool boards?
Hoter U Grey is certified for EPS, graphite EPS, and XPS. Mineral wool needs a wool-rated adhesive with higher vapour permeability engineered for the slab structure, so specifying the correct grade keeps the system inside its certification envelope and protects the A1 fire performance of the wool layer. Roker U Grey is the wool-and-EPS-rated alternative in the same range, and the EPS adhesive selection guide walks through the decision by board type.
Do I still need mechanical fixings if the adhesive is this strong?
Yes — certified ETICS installations rely on mechanical anchors to manage wind-load pressures and long-term structural movement regardless of adhesive grade. Install the fixings through the boards after the bonding layer has fully cured, typically at least 24 hours, then apply the reinforced basecoat over the anchor heads so they are fully encapsulated. The combination of adhesive bond and fixings forms the dual-retention system the certification requires.
Does the substrate need priming before bonding the boards?
Dense, well-cured concrete and clean fair-faced brick generally accept the adhesive directly, so no primer is needed. Absorbent, dusting, or chalky substrates — aerated concrete blocks, old painted renders, or weathered lime coatings — should be sealed with a consolidating wall primer beforehand so suction is even and the mortar cures at full bond strength across the whole elevation.
How long can I store unopened bags on site?
Sealed bags keep for 12 months from the manufacture date when stored off the ground in dry conditions, ideally on a pallet under a weather sheet rather than on bare concrete. Once a bag is opened, transfer unused powder into a sealed plastic tub the same day, since humid UK air reduces the pot life and bond strength of partially used bags within a week.
Technical Documentation — Atlas Hoter U Grey TDS and DoP