Fibre reinforcement in a cementitious basecoat is a narrower benefit than most product copy suggests, and the narrowness is what makes it worth understanding. The manufacturer sheets claim one thing for it — resistance to cracking — and claim nothing for it on adhesion, coverage or bond strength.
This guide takes the fibre question apart using only documents fetched this session: two editions of the Atlas Hoter U technical sheet, the Ceresit ZU sheet as the non-fibre comparator, and BBA Agrément Certificate 13/5018. Where the documents disagree with each other, that disagreement is reported rather than smoothed over. The Renders World EPS adhesives basecoats range holds both the fibre-reinforced and the plain cementitious options, so the comparison below is between products a specifier can actually put side by side on one order.
What Fibre Reinforcement Actually Adds to a Basecoat Layer
Fibre-enhanced basecoats earn their place on one documented property: the Atlas Hoter U sheet claims increased resistance to micro-cracking at the initial setting stage and to cracking during service life, across a reinforced layer of 2 mm to 5 mm. That is the whole of the manufacturer's fibre claim, and it is a real one — the reinforced layer is the part of an EWI build-up that shrinks as it cures and moves as the facade cycles.
What the fibre does not do is raise the bond. Atlas states minimum adhesion of 0.25 MPa to concrete and 0.08 MPa to expanded polystyrene for Hoter U. Ceresit ZU, which carries no fibre claim at all, states ≥ 0.25 MPa and ≥ 0.08 MPa to the same two substrates under ETAG 004. The two figures match exactly, which is the single most useful thing on this page: a buyer paying a premium for fibre is buying crack behaviour, not grip.
- Where fibre reinforcement is doing work: the reinforced layer at 2–5 mm, during the first set and through subsequent thermal movement, per the Atlas sheet's own wording.
- Where it is not the deciding factor: adhesion to substrate and to board, where the fibre-reinforced and plain products publish identical minima.
- What the fibre never replaces: the glass-fibre mesh. Both Atlas editions specify mesh embedded in the mortar with a minimum 10 cm overlap, plus 20 × 35 cm diagonal strips at 45° across opening corners. The whole-layer method sits in the basecoat and mesh reinforcement layer guide.
Vapour permeability is claimed for Hoter U on both sheet editions, stated as a property rather than a figure — no Sd value or class appears on either, so none is published here.
Four Criteria for Judging a Fibre-Reinforced Adhesive
The advantages of a fibre-reinforced adhesive are easiest to assess against criteria the documents can answer. Broader adhesive selection — foam against cementitious, board type, substrate condition — belongs to the guide to choosing the right adhesive for EPS; the four below are the ones where fibre content is the variable.
- Working time on the scaffold. Hoter U gives approximately 4 hours of working time from mixing, with a minimum 25-minute open time and a 5-minute maturing pause. Ceresit ZU gives a pot life of up to 90 minutes. On a large elevation that difference reshapes how much is mixed at once, and it favours the fibre-reinforced product for reasons unconnected to the fibre.
- Board thickness the product covers. The Hoter U sheet states the mortar fixes EPS boards up to 500 mm and XPS boards up to 200 mm. Read that alongside the certified scope: BBA 13/5018 describes the Atlas/Aval EPS system with white EPS from 20 to 300 mm and grey EPS from 25 to 200 mm, and the constructions in its reaction-to-fire table are limited to 250 mm maximum EPS thickness. Two scopes, and the certified one is the tighter of them.
- How the certificate names the product. BBA 13/5018 lists Atlas Hoter U (Aval KT 55) as both an adhesive and a basecoat within the Atlas/Aval EPS External Wall Insulation System, at 4.0 to 5.0 kg/m² adhesive coverage and 2.0 to 5.0 mm basecoat thickness. That is component status inside a certified system, and it is the accurate way to describe it — the certificate belongs to the system, not to the bag. The certificate is published in full by Atlas as BBA Agrément Certificate 13/5018.
- Fire, at the right scope. The certificate's Table 4 sets out constructions achieving B-s1, d0 and B-s2, d0 to EN 13501-1 in which Hoter U is the named adhesive and basecoat, with EPS to 250 mm maximum. Those classifications describe the construction, not the mortar, and the certificate restricts use in England, Wales and Northern Ireland to buildings with no storey more than 18 m above ground, and in Scotland to buildings with no storey 11 m or more.
The Fibre-Reinforced Options and What Separates Them
Three products carry the conversation in the Renders World range, and the honest ranking runs on what the documents support rather than on how they are marketed.
Atlas Hoter U Grey — the documented fibre-reinforced choice
Atlas Hoter U Grey 25 kg is the product both fetched sheets describe: a 2-in-1 mortar for bonding EPS and XPS boards and for forming the reinforced layer over them, with the crack-resistance claim above and raised polymer dispersion content credited for its adhesion to mineral substrates, including sound existing paint coatings. Consumption is stated as 4.0–5.0 kg/m² for bonding and 3.0–3.5 kg/m² for the reinforced layer.
One caution from the sheet is worth carrying to site because it costs nothing to observe: warm graphite EPS should not be bonded, and graphite boards should not be allowed to heat up during fitting or initial set, since that can cause the board to release from the adhesive. Storing EPS insulation boards shaded and working the sunny elevation early handles it entirely.
Atlas Hoter U White — a strength difference, not a colour one
Atlas Hoter U White 25 kg is the same product on white cement rather than grey. Both sheet editions give the same reason for the white version, and it is not the one usually quoted: using white cement increases the strength of the layer formed from the adhesive. No fetched document mentions basecoat show-through beneath pale renders, so that argument is left off this page. Specify white for the stated strength benefit, and treat any colour reasoning as a site preference rather than a manufacturer position.
Roker U Grey — where mineral wool enters the build-up
The Hoter U sheet is explicit that mineral wool boards, both lamella and facade types, are outside its scope and direct the specifier to the Atlas Roker system instead. That makes Roker U Grey 25 kg the route on a wool elevation. No Roker U document was retrieved this session, so no adhesion value, thickness limit, vapour figure or fibre claim is published for it here — the routing is documented, the specification is not, and it should be confirmed from the bag before ordering.
Fibre-Reinforced Against Plain Cementitious, Figure by Figure
Every cell below is copied from a document fetched this session. Blank claims are shown as omitted rather than filled from a comparable product.
| Property | Atlas Hoter U (fibre-reinforced) | Ceresit ZU (no fibre claim) |
|---|---|---|
| Fibre content stated | Yes — see the divergence noted below | None stated |
| Adhesion to concrete | min. 0.25 MPa | ≥ 0.25 MPa (ETAG 004) |
| Adhesion to EPS | min. 0.08 MPa | ≥ 0.08 MPa (ETAG 004) |
| Working time from mixing | approx. 4 hours | pot life up to 90 minutes |
| Reinforced layer thickness | 2 mm min / 5 mm max | Not stated on the sheet |
| Bonding consumption | 4.0–5.0 kg/m² | approx. 5.0 kg/m² |
| Reinforced-layer consumption | 3.0–3.5 kg/m² | approx. 4.0 kg/m² |
| Application temperature | +5 °C to +25 °C — see divergence below | +5 °C to +25 °C |
| Reinforced layer after bonding | not earlier than 3 days | after 3 days |
Two divergences, both worth acting on. The 2016 edition of the Hoter U sheet describes the mortar as reinforced with cellulose fibres; the 2021 edition names only structural fibre reinforcement and micro-fibres, without a material. Neither edition mentions polypropylene or glass. The same two editions give different application ceilings — +5 °C to +25 °C in 2016, +5 °C to +30 °C in 2021 — and the table above carries the stricter of the two. Order against the sheet edition printed for the bag in front of you, and where a specification hangs on fibre type, ask Atlas to confirm it in writing.
Working Out Quantities and Making the Call
Combined consumption for both stages is 4.0–5.0 + 3.0–3.5 = 7.0–8.5 kg/m². For 100 m² of facade that gives 100 × 7.0–8.5 = 700–850 kg, and 700–850 ÷ 25 = 28–34 bags. For a 60–80 m² semi-detached, 60 × 7.0 = 420 kg and 80 × 8.5 = 680 kg, so 420 ÷ 25 = 17 and 680 ÷ 25 = 28 — a genuine 17 to 28 bag span, because the sheet ties actual consumption to substrate evenness and bonding technique rather than to floor area alone. Measure the wall properly and the range narrows quickly.
- Specify Hoter U Grey where the boards are EPS or XPS, one product should serve both bonding and the reinforced layer, and the documented crack resistance is worth having. It is the fibre-reinforced product with two fetchable sheets and named component status in BBA 13/5018.
- Specify Hoter U White where the added layer strength from white cement is wanted, which is the reason the sheets themselves give for the variant.
- Specify Roker U the moment mineral wool appears on any elevation, because the Hoter U sheet routes wool to the Roker system rather than covering it.
- Specify Ceresit ZU where the fibre claim is not the priority and the shorter 90-minute pot life suits how the crew works, since the adhesion minima are the same.
Where the programme runs cold and the +5 °C floor is the obstacle rather than crack behaviour, a polyurethane foam at the bonding stage is a different answer to a different problem, set out in the comparison of foam and traditional adhesives.
Key Takeaway: Fibre reinforcement in a basecoat buys documented crack resistance in the 2–5 mm reinforced layer and nothing measurable on bond — Atlas Hoter U and Ceresit ZU publish identical adhesion minima of 0.25 MPa to concrete and 0.08 MPa to EPS. Two editions of the Hoter U sheet disagree on fibre type and on the temperature ceiling, so confirm both against the bag before a specification depends on them.
Written by Mariusz Saja. Technically reviewed by Rafał Wyrzykowski. Last reviewed Aug 2026.
Fibre-Reinforced Basecoat Questions
What type of fibre is in Atlas Hoter U?
The 2016 edition of the technical sheet describes the mortar as reinforced with cellulose fibres, while the 2021 edition refers only to structural fibre reinforcement and micro-fibres without naming the material. Neither names polypropylene or glass, so no fibre type is stated as settled on this page. Where a specification turns on it, ask Atlas to confirm against the current production sheet.
Does a fibre basecoat bond better than a standard one?
On the published minima, no. Atlas Hoter U states minimum 0.25 MPa to concrete and 0.08 MPa to EPS, and Ceresit ZU states ≥ 0.25 MPa and ≥ 0.08 MPa to the same substrates under ETAG 004. The fibre claim covers resistance to micro-cracking at initial set and cracking in service, which is a separate property from bond.
How many bags do I need for a three-bedroom semi?
At combined consumption of 7.0–8.5 kg/m² across both stages, a 60–80 m² facade works out at 420–680 kg, or 17 to 28 bags of 25 kg. The sheet ties real consumption to substrate evenness and bonding technique, so a measured survey of the actual wall area minus openings will tighten that range considerably.
Can Atlas Hoter U be used on mineral wool boards?
The sheet places both lamella and facade mineral wool outside the product's scope and directs the specifier to the Atlas Roker system instead. On a mixed build-up with wool on some elevations, Roker U Grey is the documented route, and confirming its own figures from the bag before ordering keeps the specification clean.
What temperature can it be applied at?
The stricter of the two sheet editions gives +5 °C to +25 °C for the mortar, the substrate and the surroundings during work, and the later edition gives +5 °C to +30 °C. Both editions also rule out working during snow, rain or strong wind, and call for sheeted scaffolding throughout, which is the practical way to hold those conditions steady.