Description
Atlas Hoter U Grey 25 kg is the fibre-reinforced, 2-in-1 cement adhesive and basecoat mortar that bonds EPS and XPS insulation boards and embeds fibreglass mesh in one product, delivering certified adhesion of ≥ 0.25 MPa to concrete with an extended 4-hour pot life. Sold within the professional EPS adhesives and basecoats range at Renders World, this grey-cement mortar belongs to the certified Atlas ETICS family and is specified by UK trade installers on retrofit and new-build EWI projects where crack resistance, long working time, and full system compatibility decide the spec.
Where Atlas Hoter U Grey Performs Best — UK EPS and XPS Walls
Atlas Hoter U Grey 25 kg 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. On a typical 100 m² elevation, one bag code covers both the bonding and the reinforcement stage — simplifying procurement and reducing stock-keeping on site.
The grey-cement formulation suits projects where the final 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 graphite EPS façades, on extruded polystyrene plinth zones, and on mineral-substrate solid-wall retrofits over brick or concrete block, this is the workhorse mortar that consistently delivers the bond strength and crack control trade specifiers expect.
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 gantry.
- 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. The benefits of fibre-enhanced basecoats guide explains why this matters on tall elevations.
- 4-hour pot life at 20 °C: Mixed mortar stays workable for around four hours, so a two-person team can mix bigger batches and apply 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 UK jobs where Building Control and warranty providers verify the spec.
- 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.
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 |
| Standards | EN 15824:2017 · ETA-certified within Atlas ETICS |
| Application | Hand trowel or rendering machine |
| Shelf life | 12 months, sealed, dry storage |
How to Apply Atlas Hoter U Grey — Mixing Ratio, Pot Life, Coverage
Mix the 25 kg bag into 5.0–5.5 litres of cool, clean water using a paddle mixer on low speed until the paste is lump-free, then rest for five minutes and remix briefly to activate the polymers. For board fixing, apply the mortar in a 3–4 cm perimeter band with three to six central dots, then press the board against the wall until contact covers at least 40 % of the rear face — the figure that satisfies the certified Atlas ETICS detail.
After the bonding layer has cured (typically 24 hours) and mechanical fixings are installed, 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 over the top so the mesh sits in the outer third of the layer. The complete basecoat and mesh reinforcement layer guide covers overlap discipline, corner detailing, and the diagonal mesh patches around openings.
Installation Notes — Conditions, Drying Times, Finishing
Atlas Hoter U Grey performs best between +5 °C and +25 °C, with both substrate and ambient temperatures inside that range for at least 24 hours after application. On dense, well-cured concrete the mortar bonds directly; on absorbent or dusting substrates such as aerated concrete or old lime renders, a coat of Atlas Uni-Grunt primer evens out the suction so the adhesive cures at full strength across the elevation.
Schedule basecoat work for overcast conditions or shaded scaffolding where possible — direct midday sun on dark graphite EPS can flash-dry the thin mortar layer before the mesh is properly embedded, weakening the bond between mortar and fibre. Allow the finished basecoat to cure for a minimum of three days before priming and applying the decorative thin-coat render, extending that window in cool or humid weather so the surface is fully ready for the quartz primer, which is the moment the basecoat starts paying back the time invested in curing it properly.
Pro Tips From UK Installers Using Atlas Hoter U Grey
- Mix to the workboat, not the bag. Two-thirds of a 25 kg bag in one bucket gives a stiffer first mix that thins down predictably with the remaining water — easier to control than chasing the 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 basecoat 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 the 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 window reveals and verges saves twenty minutes of trowel correction later and keeps the bead nose crisp.
Is Atlas Hoter U Grey Right for Your Project?
- Atlas Hoter U Grey is the right call when your EWI build-up uses EPS, graphite EPS, or XPS boards and you need one certified adhesive and basecoat across the elevation, with a long working time that suits batch mixing on larger jobs.
- Going under a light-coloured finish? The white-cement 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 within the same range.
- For full-system specification, pair Atlas Hoter U Grey 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, 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 around 450 kg + 350 kg = 800 kg of mortar, which works out to 32 bags. Order 35 bags per 100 m² to absorb the 10 % wastage that typically comes with uneven substrates, complex window detailing, and offcut losses on long basecoat runs.
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, which is 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 the mortar starts to stiffen.
Can I use Atlas Hoter U Grey to bond mineral wool boards?
Atlas Hoter U Grey is certified for EPS, graphite EPS, and XPS — for mineral wool elevations the specification calls for a wool-rated adhesive with higher vapour permeability, and our guide to choosing the right adhesive for EPS and wool systems walks through that decision. Using the correct adhesive grade keeps the system inside its certification envelope and protects the A1 fire performance of the wool layer.
Do I still need mechanical fixings if the adhesive is this strong?
Yes — certified ETICS installations in the UK 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 24 hours minimum), then apply the reinforced basecoat over the anchor heads so they are fully encapsulated.
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 required. Absorbent, dusting, or chalky substrates — such as aerated concrete blocks, old painted renders, or weathered lime coatings — should be sealed with a wall primer beforehand so suction is even and the mortar cures at full bond strength across the 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 directly on bare concrete. Once a bag is opened, transfer any unused powder into a sealed plastic tub the same day — humid UK air will reduce the pot life and bond strength of partially used bags within a week.
Technical Documentation — Atlas Hoter U Grey TDS and DoP
- Atlas Hoter U Grey — Manufacturer Technical Data Sheet (PDF, atlas.com.pl)
- Atlas Hoter U — Product Page and Declaration of Performance (atlas.com.pl)