Description
Atlas Hoter U Grey Adhesive with Fibre 25 kg — ETA-Certified 2-in-1 EPS Basecoat and Bonding Mortar
Product Overview
A single 25 kg bag of Atlas Hoter U Grey handles both stages of an EWI insulation build-up — bonding EPS or XPS boards directly to masonry and embedding fibreglass mesh into the reinforced basecoat layer — delivering ETA-certified adhesion of ≥ 0.25 MPa to concrete and an extended 4-hour pot life as a core component of the Atlas ETICS system — the fully certified EWI assembly that satisfies UK Building Control and warranty requirements. Part of the professional EPS adhesive and basecoat range at Renders World, this cement-based mortar is fortified with advanced 3D structural microfibres for exceptional crack resistance and impact durability, making it the preferred choice for UK trade installers executing flawless thermal retrofits and new-build installations.
Each bag covers approximately 5 m² for board fixing (at 4.0–5.0 kg/m²) or 7 m² for basecoat mesh embedding (at 3.0–3.5 kg/m²), mixing effortlessly with 5.0–5.5 litres of clean water to form a smooth, highly workable paste. Compatible with both standard white EPS and graphite-enhanced polystyrene boards, as well as extruded polystyrene (XPS), Atlas Hoter U provides the tested, highly vapour-permeable adhesive layer that keeps walls breathing naturally for a healthier indoor environment, while meeting the rigorous technical standards that Building Control and warranty providers require on compliant EWI installations across the UK.
Key Benefits
- Two Jobs from One Bag: Bonds EPS and XPS insulation boards securely to the substrate and creates the reinforced basecoat layer with embedded mesh — keeping material logistics simple, reducing site waste, and ensuring seamless compatibility between the bonding and reinforcing stages.
- Crack-Resistant 3D Fibre Layer: Built-in structural microfibre reinforcement within the mortar matrix distributes mechanical stress across the cured basecoat, significantly reducing the risk of hairline cracking from thermal expansion, structural settlement, or surface impacts. For more technical insights, read our guide on the benefits of fibre-enhanced basecoats.
- Extended 4-Hour Working Time: An exceptionally long 4-hour pot life at standard temperatures means the mixed mortar stays workable longer than standard adhesives, allowing installers to mix larger batches, work at a more comfortable pace, and minimise wasted material that sets prematurely in the bucket.
- High Adhesion Strength: Grips reliably on difficult substrates — including old brick, painted masonry, and mixed-surface walls — thanks to a high polymer-dispersion content (meaning the bond holds firm even where older surfaces are uneven), keeping your insulation securely in place through decades of UK weather.
- Highly Vapour Permeable: The cured mortar breathes actively, allowing trapped moisture to escape from the wall assembly and preventing condensation buildup within the insulation system, which protects both the masonry structure and the indoor air quality.
- Universal EPS and XPS Compatibility: Engineered and tested to bond both standard and graphite-enhanced EPS, as well as dense XPS perimeter boards, meaning contractors can use a single trusted adhesive across the entire building envelope regardless of the specific polystyrene grade chosen.
Technical Specifications
| Property | Value |
|---|---|
| Product Type | Cement-based adhesive and reinforcing mortar (2-in-1) |
| Composition | Grey cement, mineral fillers, polymer modifiers, microfibres |
| Pack Size | 25 kg bag |
| Colour | Grey |
| Mixing Ratio | 5.0–5.5 litres water per 25 kg bag |
| Pot Life | Approx. 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 / Mesh | 3.0–3.5 kg/m² (≈ 7 m² per bag) |
| Reinforced Layer Thickness | 2–5 mm |
| Adhesion to Concrete | ≥ 0.25 MPa |
| Certification / Standards | ETA-certified (Atlas ETICS) / EN 15824:2017 ★ 2026 |
| Application Method | Trowel (hand) or machine |
| Shelf Life | 12 months in dry conditions, original sealed packaging |
Application & Compatibility
Atlas Hoter U performs best when mixed to a lump-free consistency and applied to clean, structurally sound mineral substrates — such as brick, concrete, and existing renders — that are free from dust, oil, and loose materials that could compromise the bond. For a complete system, pair this adhesive with Atlas 150 g/m² fibreglass mesh to form the impact-resistant basecoat layer that protects the insulation and provides a stable canvas for the final decorative finish. A comprehensive overview of how adhesive mortars integrate into the broader facade system is available in our adhesive selection guide for EPS insulation.
- Stage 1 — Bonding Insulation Boards: Apply the mortar using the perimeter-and-dot method — a continuous band of adhesive 3–4 cm wide along the board's edges, combined with 3 to 6 patches (dots) evenly distributed in the centre. Once pressed against the wall, the adhesive must cover at least 40% of the board’s rear surface to ensure secure, ETA-compliant bonding. For perfectly flat substrates, a notched trowel (10–12 mm) can be used to apply a full-surface adhesive bed.
- Stage 2 — Reinforced Basecoat Layer: After the bonding layer has fully set (usually 24 hours), install the required mechanical fixings and lightly sand the board joints. Apply a 2–3 mm continuous layer of Atlas Hoter U using a stainless steel trowel, press the fibreglass mesh into the wet mortar (ensuring minimum 100 mm overlaps at all mesh joints), and immediately smooth over a second thin pass to fully embed the mesh. The basecoat and mesh reinforcement guide outlines proper overlapping and corner detailing techniques.
- Substrate Priming: A coat of Atlas Uni-Grunt primer on highly absorbent or dusting substrates — such as aerated concrete or old lime renders — regulates suction evenly so the adhesive cures at full strength across the entire elevation. On dense, well-cured concrete, Hoter U bonds directly without needing a primer.
- System Context: For a complete system, pair Atlas Hoter U Grey with graphite or standard EPS insulation boards as the thermal layer, followed by Atlas Cerplast quartz primer and an Atlas decorative thin-coat render (such as silicone or acrylic). Keeping all components within the certified Atlas ETICS ecosystem ensures full compatibility and protects your manufacturer warranty.
Installation Notes
Mix the 25 kg bag gradually into 5.0–5.5 litres of cool, clean water using an electric paddle mixer on a low speed until a smooth, uniform paste is achieved, then allow the mixture to rest for 5 minutes before briefly remixing to activate the polymers. For the most resilient cure, schedule the basecoat application during overcast conditions or shade the scaffolding, as direct midday sun on dark graphite EPS boards can cause the thin mortar layer to flash-dry and weaken before the mesh is properly embedded. Keeping the freshly applied basecoat sheltered from rain, wind, and frost for 24 hours — with ambient and wall surface temperatures between +5 °C and +25 °C — gives the mortar the stable curing conditions that produce the strongest, most crack-resistant bond.
Trade Insight — Installer's Note
The standout feature of Atlas Hoter U is undoubtedly its generous 4-hour pot life — a massive advantage on large commercial elevations or during warmer UK summer days where standard 90-minute adhesives leave you rushing. Because the mortar stays highly plastic in the tub for longer, a solo installer or small team can mix larger volumes at the station and apply vast stretches of basecoat without the constant interruption of mixing fresh batches. Furthermore, the structural microfibres in the mix are formulated to lay flat under the trowel rather than snagging, resulting in an exceptionally smooth finish that requires less sanding and consumes noticeably less quartz primer during the next stage of the build.
Is This Product Right for Your Project?
- Choose Atlas Hoter U Grey 25 kg if your EWI specification uses expanded (EPS) or extruded (XPS) polystyrene boards and you need a high-performance, fibre-reinforced 2-in-1 adhesive that offers an exceptionally long working time within a fully certified Atlas facade system.
- Need a white cement basecoat? The Atlas Hoter U White 25 kg provides identical bonding and 3D fibre-reinforcement properties but is based on premium white cement, which prevents grey show-through and eliminates the need for tinted primers under light-coloured decorative renders.
- Insulating with mineral wool instead of polystyrene? Mineral wool slabs are heavier and require a much higher vapour permeability than EPS adhesives can provide. A dedicated mineral wool adhesive such as Roker U grey 25 kg, available in the same collection, ensures the highly breathable, secure bond required for A1-rated non-combustible systems.
Frequently Asked Questions
How many bags of Atlas Hoter U Grey do I need per 100 m² of EWI?
A standard 100 m² installation requires adhesive for both board fixing and creating the reinforced basecoat. Calculating at average consumption rates (4.5 kg/m² for fixing and 3.5 kg/m² for basecoating), the project requires 450 kg + 350 kg = 800 kg total. Dividing this by 25 kg yields exactly 32 bags, though we recommend ordering 35 bags per 100 m² to account for 10% wastage, uneven substrates, and complex detailing around windows and doors.
Can Atlas Hoter U be used to fix mineral wool insulation boards?
Atlas Hoter U is engineered and certified specifically for EPS and XPS boards, where its fibre-reinforced formula delivers its best performance. Mineral wool projects have distinct breathability and weight requirements that are perfectly served by a purpose-built adhesive — Atlas Roker U is certified for mineral wool boards up to 300 mm as well as EPS up to 500 mm, so specifying Roker U for mineral wool elevations keeps the system fully compliant and the facade protected for the long term.
How long does the mixed mortar stay workable?
Once mixed with the correct ratio of water, Atlas Hoter U offers an exceptionally long pot life of approximately 4 hours at a standard temperature of 20 °C. This extended working window is highly beneficial for tradespeople, allowing for larger batch mixing and steady, unhurried application across wide elevations without the mortar stiffening prematurely in the bucket.
Does this adhesive system require mechanical fixings?
Yes, mechanical fixings (insulation dowels/anchors) are a mandatory requirement for certified ETICS installations in the UK to manage wind-load pressures and structural movement. You should install the fixings through the insulation boards after the Atlas Hoter U adhesive has fully cured (typically a minimum of 24 hours), prior to applying the reinforced basecoat layer over the top.
Is Atlas Hoter U safe to handle and environmentally responsible?
Atlas Hoter U is formulated to strictly comply with European environmental and safety regulations, containing no harmful solvents or toxic volatile organic compounds (VOCs). Because it is a cement-based product, the wet mix is alkaline, meaning installers must wear standard PPE (gloves and safety glasses) to prevent skin and eye irritation; however, once fully cured, the mortar is completely inert, environmentally safe, and will not leach contaminants into the surrounding soil or masonry.
