Description
Atlas Hoter U is the fibre-reinforced cement mortar that does both structural jobs of an insulated facade from one bag: it bonds the boards to the wall, then carries the mesh in the reinforced layer over them. The grey-cement version of Atlas Hoter U sits in the EPS basecoat range at Renders World, and the white-cement version of the same mortar is stocked beside it.
Where Atlas Hoter U Belongs on a UK Insulated Facade
Atlas Hoter U bonds EPS and XPS at 4.0–5.0 kg/m² and forms the mesh layer at 3.0–3.5 kg/m², so one bag code covers both ETICS stages on an elevation. Atlas builds it from a cement binder, graded aggregates and modifiers, with fibre reinforcement through the mix.
The fibres are credited with two specific things rather than a general claim: they hold the mortar together against microcracking at the initial setting stage, and against cracking later in the system's service life, which is what keeps a thin reinforced layer intact across a tall elevation. The high adhesion has a stated cause as well — a raised polymer dispersion content, helped by a graded, tight aggregate packing.
The Atlas Hoter U sheet is unusually explicit about where the mortar belongs, and the boundaries are worth as much as the permissions.
| Scope | What the sheet declares |
|---|---|
| Boards it takes | White EPS, graphite EPS, XPS |
| Board thickness | EPS to 50 cm; XPS to 20 cm |
| Boards it refuses | Mineral wool, lamella and facade alike |
| Masonry substrates | Aerated concrete, silicate, ceramic, block, stone |
| Concrete and plaster | Cast and precast concrete; cement and cement-lime plaster |
| Painted walls | Permitted, adhesion assessed each time |
| System types | Thin-coat, renovation over EPS, ceramic |
| Tiled finishes | Ceramic tiles to 0.36 m² |
| Height limit | Over 25 m the sheet routes to Atlas Roker |
Two of those rows decide projects. Mineral wool goes to the Roker system, and the wool-rated adhesive is stocked in the same range — a hard boundary, not a preference. Buildings taller than 25 m are routed away from Atlas Hoter U as well, with one exception the sheet states: buildings of up to 11 storeys handed over before 1 April 1995 may still be insulated with EPS. Underground garages and ceilings under heated rooms go to Atlas Roker G.
Matching mortar to board type is the whole decision at this stage, and the adhesive selection guide for EPS boards works through it by board and by substrate. The boards themselves sit in the graphite EPS insulation boards range, and mineral wool slabs pair with Roker U grey adhesive instead.
Why Specifiers Choose the Grey 25 kg Bag
- One mortar, two stages. Atlas declares both functions in the system — fixing the insulation, and forming the reinforced layer beneath all its thin-coat renders — so procurement runs off a single bag code.
- Bond strength stated on both faces. Minimum 0.25 MPa to concrete and minimum 0.08 MPa to polystyrene in the air-dry state, which is the pair a fixing calculation rests on.
- Around four hours of working time. Long enough to mix a station batch and run a bay, with 25 minutes of open time governing the mesh work itself.
- Fibre reinforcement with a named purpose rather than a marketing line: the fibres are what hold the cured layer together across a tall elevation.
- Vapour permeable, and declared frost resistant and water resistant for external walls.
- Named in certified systems: ETA 06/0081 for the Atlas system, ETA 07/0316 for Atlas XPS, and two Polish national assessments in the edition now in force.
The fibre question is worth understanding rather than taking on trust, and the basecoat and mesh reinforcement layer guide sets out what the reinforcement changes in the cured layer.
Atlas Hoter U Specifications, Edition of 25 August 2026
| Property | Value as published by Atlas |
|---|---|
| Composition | Cement binder, aggregates, modifiers, fibres |
| Bulk density, dry mix | Approx. 1.40 kg/dm³ |
| Mixing ratio | 0.20–0.22 l water per kg |
| Water per bag | 5.00–5.50 l per 25 kg |
| Maturation time | Approx. 5 minutes, then remix |
| Working time of mixed mortar | Approx. 4 hours |
| Open time | Minimum 25 minutes |
| Adhesion to concrete, air-dry | Minimum 0.25 MPa |
| Adhesion to polystyrene, air-dry | Minimum 0.08 MPa |
| Reinforced layer thickness | 2 mm minimum, 5 mm maximum |
| Consumption, bonding boards | 4.0–5.0 kg/m² |
| Consumption, reinforced layer | 3.0–3.5 kg/m² |
| Working temperature | +5 °C to +30 °C |
| Packaging | 25 kg paper bags |
| Shelf life | 12 months from the production date |
| System approvals | ETA 06/0081 and ETA 07/0316 |
| National assessments | ITB-KOT-2020/1616 and ITB-KOT-2018/0385 |
The starred values in the manufacturer's own table — working time, open time and both adhesion figures — are recommended for application at roughly 20 °C and 55 % relative humidity, which is the condition Atlas ties them to.
Where the Older Sheet Differs, and What It Changes on Site
Atlas Hoter U has two technical sheets in circulation. The edition in force carries the date 25 August 2026 and closes with the sentence that all previous editions lose validity. The one still mirrored by distributors carries the date 19 February 2021. Three of the differences change what a contractor does.
- Bonded area. The older edition asks for at least 40 % of the board face, rising to a minimum 60 % once the board is pressed home. The current edition states 40 % and no second figure. Working to 60 % satisfies both.
- Graphite boards. The 2021 sentence about graphite boards under the reinforced layer breaks off unfinished. The current edition completes it: sand the boards and remove the dust first.
- National assessments. Four were named in 2021, two in the edition now in force.
Where the two disagree, the stricter reading leads and carries the date of the edition it comes from. One figure sits only in the older edition — soluble chromium (VI) at or below 0.0002 % — and since neither the current technical sheet nor the safety data sheet repeats it, it is not stated here as a property of what is in the bag today.
How to Apply Atlas Hoter U — Bonding, Then the Reinforced Layer
Atlas Hoter U is mixed in one pass. Empty the bag into measured water, mix with a low-speed paddle to a uniform consistency, stand it for about five minutes, scrape the unmixed material off the vessel wall and remix. Use the batch within roughly four hours, working between +5 °C and +30 °C.
Preparing the wall
The substrate must be unfrozen, dry, stable, seasoned and clean of dust, dirt, lime, oils, grease, wax and paint residue. Hollow-sounding plaster is removed without exception. Paint coatings with low adhesion come off mechanically, and hydrodynamic washing is the method the sheet names. Where fungi, algae or lichen are present, the surface is cleaned mechanically and then treated with Atlas Mykos Plus.
Larger irregularities are filled beforehand with a levelling mortar; Atlas names ZW 330 for the job. Absorbent or unevenly absorbent walls are primed, and priming is required outright on weak cement and cement-lime plasters and on aerated concrete, silicate block and slag-block walls. Three primers are named: Grunt NKP, which is used as supplied without dilution, Uni-Grunt, and the concentrate Uni-Grunt Ultra.
Two building types get their own instruction. On large-panel construction the inter-panel joints are assessed as well as the wall face, and any sealant that can react chemically with the insulation is removed. On prefabricated sandwich panels the original fixing of the facing layer is assessed and, where needed, strengthened by additional anchoring — assessment and design by someone holding structural qualifications.
Bonding the boards
- Fix and level the base track first — it forms the bottom edge of the insulation.
- Apply the mortar to the board, never to the wall: a perimeter band at least 3 cm wide along the edge, plus 6 to 8 dabs of at least 8 cm diameter across the rest of the face.
- Hit the coverage figure. At least 40 % of the board face is bonded, and the older edition puts the figure after pressing at a minimum of 60 %. Keep the bed under a pressed board to no more than 10 mm.
- Set out in staggered vertical joints, offer the board up immediately after buttering and beat it into position with a straightedge.
- On flat, smooth substrates a notched trowel of at least 10 × 10 mm across the whole board face is permitted instead of band-and-dab.
- Mechanical fixings come no earlier than 24 hours after bonding, with plastic or steel pins to the thermal design and never fewer than 4 per m².
Fixing quantity is a design output rather than a rule of thumb, and the fixing pattern and spacing guide covers how the layout is arrived at.
Forming the reinforced layer
The Atlas Hoter U reinforced layer starts no earlier than three days after the boards were bonded. Before anything goes over them, the board surface must be free of frost, level, clean, stable and dust-free — and graphite boards are sanded and dedusted at this point, which is the instruction the older sheet leaves unfinished.
Lay the mortar out evenly with a notched trowel of 6–10 mm, roll the Atlas 150 reinforcing mesh into it and bed it in with the trowel, smoothing flat in the same pass. The mesh must finish completely invisible and fully embedded, with laps of at least 10 cm. At the corners of openings, additional strips of at least 20 × 35 cm go in at 45 degrees, beneath the main reinforcing layer. Any remaining unevenness is sanded once the mortar has dried, since it will otherwise show through the render.
Rendering follows once the layer has dried, about three days, and the layer is coated with the key coat matched to the chosen render before any finish goes on. Tools wash out in clean water immediately after use, and hardened residues need the manufacturer's own cement remover.
Site Conditions, Graphite Boards and Testing a Doubtful Wall
Three Atlas Hoter U instructions carry more weight on site than anything in the data table.
- Never bond heated graphite EPS. Atlas is explicit: do not let graphite boards warm during installation or during the adhesive's initial set, because heating at either stage can separate the board from the mortar. Sequencing dark boards to follow the shade is the practical answer.
- Sheet the scaffold. Covers are necessary during the works, and no work is carried out in snow, rain or strong wind.
- Test a wall you are unsure of. Where a substrate is weak, dusting or hard to clean, bond polystyrene cubes of 10 × 10 × 10 cm at representative points and check the joint after three days, or after five days below 10 °C and above 80 % humidity.
That test reads one way only. If the polystyrene tears when pulled by hand, the substrate is sound. If the cube comes away carrying the mortar and a layer of the wall with it, the wall is not load-bearing, and how the weak layer is dealt with belongs in the thermal design rather than on the scaffold.
Fire Classification and Certification Scope
Neither edition of the technical sheet gives a reaction-to-fire class for Atlas Hoter U on its own. The class belongs to a complete build-up, and BBA Agrément Certificate 13/5018 for the Atlas/Aval EPS External Wall Insulation System is where it is declared. No product is BBA certified; a system is.
What makes the certificate readable here is that this mortar appears in the same row twice — as the adhesive, under its system designation Aval KT 55, and again as the basecoat. Built from products stocked in this range, that row is the build-up below.
| Role in the certified build-up | What it is |
|---|---|
| Adhesive | Hoter U, as Aval KT 55 |
| Insulation | EPS to a maximum 250 mm |
| Basecoat | Hoter U |
| Mesh | Atlas 150 or Atlas 165 |
| Key coat | Cerplast |
| Finishing coat | Atlas Cermit mineral or silicone render |
| Classification | B-s2, d0 to EN 13501-1:2010 |
The certificate allows further Atlas mortars in the adhesive, basecoat and key-coat roles, and those are not listed here because this shop does not carry them. It also does not say which pairing of key coat and finishing coat was tested, so the classification stays attached to the assembly as a whole and is narrowed no further. The EPS insulation in isolation is classified E.
Two storey limits come with that certificate. In England, Wales and Northern Ireland the system should not be used on buildings with a storey more than 18 m above ground level. In Scotland the limit is a storey 11 m or more above ground level, or a position within 1 m of a boundary, subject to the conditions the certificate sets out. Impact resistance is certified per construction as well, and those rows cannot be tied to one build-up, so no impact category is stated.
Grey or White, and Where Mineral Wool Changes the Answer
Renders World stocks both versions, and they share one formulation and one technical sheet; the cement is the variable. Atlas states that white cement increases the strength of the layer formed from the adhesive, and says nothing that would separate the two on any other property.
| Your project | What to specify | Deciding line |
|---|---|---|
| EPS or XPS facade, mid or dark finish | Atlas Hoter U grey 25 kg | Grey cement, min. 0.25 MPa to concrete |
| EPS or XPS where layer strength leads | Atlas Hoter U White 25 kg | White cement, stronger cured layer |
| Mineral wool slabs, any elevation | Roker U on the Atlas Roker system | This mortar is not rated for wool |
Ordering Atlas Hoter U — Bags per Elevation
Because Atlas Hoter U is consumed at two different rates, quantities are worked stage by stage. A 25 kg bag bonds 5.0 to 6.3 m² of board at 4.0–5.0 kg/m², and forms 7.1 to 8.3 m² of reinforced layer at 3.0–3.5 kg/m².
- Bonding 100 m²: 400–500 kg, which is 16 to 20 bags.
- Reinforced layer over 100 m²: 300–350 kg, which is 12 to 14 bags.
- Both stages together: 700–850 kg, or 28 to 34 bags, before any allowance for uneven substrates and offcuts.
Atlas ties actual consumption to how level the wall is and to the bonding method chosen, so an older, uneven elevation lands at the upper end.
Three things are worth knowing before the order goes in. Renders World processes orders the same day when the stock is there. Delivery is not calculated at checkout — the team works out the most cost-effective method after the order arrives and comes back with it. And because this mortar ships in paper bags, it sits outside the 14-day return that covers most of the catalogue, so quantities are worth settling before ordering rather than after. Collection in person from the counter during opening hours is the other route.
Store the bags closed, dry, cool, ventilated and preferably palletised, out of direct sun and away from food and drink, because the product hardens irreversibly on contact with moisture.
The mortar contains cement, and the safety data sheet classifies it as causing skin irritation, possible allergic skin reaction, serious eye damage and possible respiratory irritation. Avoid breathing the dust, wear protective gloves, clothing, eye and face protection, and keep it away from children. The hazardous constituents named are Portland cement clinker and dusts from Portland cement production.
Common Questions From the Scaffold
How many bags cover a 100 m² elevation?
Between 28 and 34 bags of Atlas Hoter U across the two stages: 16 to 20 bags to bond the boards, and 12 to 14 to form the reinforced layer. A single bag covers 5.0 to 6.3 m² when bonding and 7.1 to 8.3 m² in the mesh layer, so part-elevations scale from there.
Can this mortar bond mineral wool slabs?
No. The declared scope is white EPS, graphite EPS and XPS, and both lamella and facade wool slabs are routed to the Atlas Roker system. Specifying the wool-rated adhesive keeps the build-up inside the system it was assessed as, which matters most on projects where wool was chosen for its fire performance in the first place.
How soon after bonding can the reinforced layer go on?
Three days at the earliest. Mechanical fixings can go in from 24 hours after bonding, and rendering follows once the reinforced layer has dried, roughly a further three days, with the key coat for the chosen render applied first. Cool or humid weather extends both waits.
Anything different about graphite EPS?
Two things, and both are easy to miss. Heated graphite boards are never bonded, and they are kept from warming while the adhesive takes its initial set. Before the reinforced layer they are also sanded and dedusted.
What weather stops the work?
- Mortar, substrate and surroundings all sit between +5 °C and +30 °C.
- Snow, rain and strong wind stop bonding altogether, and covers on the scaffolding count as necessary rather than optional.
- Below 10 °C with humidity above 80 %, an adhesion test on a doubtful wall is assessed after five days instead of three.
Is there a building height limit?
Two separate limits apply, from two documents. Atlas routes buildings over 25 m to the Roker system, with an exception for buildings of up to 11 storeys handed over before 1 April 1995. BBA Agrément Certificate 13/5018 sets its own storey limits for the certified system: above 18 m in England, Wales and Northern Ireland, and 11 m or within 1 m of a boundary in Scotland.
Technical Documentation