Description
Two stages, one bag: Ceresit ZU bonds the boards and then carries the mesh, at 5.0 kg/m² and 4.0 kg/m² respectively, with a pot life of up to 90 minutes at the sheet's +23 °C reference conditions — and a set-before-mesh interval the data sheet puts at three days rather than one.
Ceresit ZU on a Ceretherm Wall — What the Mortar Does at Each Stage
Ceresit ZU mesh adhesive 25kg is the cement and lime mortar that fixes EPS boards at roughly 5.0 kg/m² and then forms the mesh-reinforced layer at 4.0 kg/m² on Ceretherm ETICS elevations. Renders World lists it in the EPS adhesives basecoats range as the Ceresit-brand route through both stages.
Henkel writes the product for expanded and extruded polystyrene within the Ceresit Ceretherm Popular system, on new build and on thermal renovation alike, and recommends white or graphite EPS boards meeting EN 13163 for external wall insulation. That board recommendation is where the mortar meets the rest of the wall, and graphite EPS insulation boards sit inside it.
The sheet is explicit about what the mortar will bond to, which is the pre-order check worth doing on any elevation:
- Sound, load-bearing walls, renders and cement substrates free of grease, bitumen, dust and anything else that reduces adhesion.
- Existing renders and paint coats only after testing — hollow render comes off, and vapour-tight or poorly adhering coatings are removed completely.
- Highly absorbent walls such as aerated concrete blocks, primed first with Ceresit CT 17 and left to dry for at least two hours, a sequence the substrate preparation guide works through wall by wall.
Why Installers Specify This Mortar for EPS Facades
- One product across both structural stages: board fixing at 5.0 kg/m² and the reinforced layer at 4.0 kg/m² come out of the same 25 kg bag, so a job runs on one code and the certification chain stays with one product.
- Declared bond to ETAG 004: min. 0.25 MPa to concrete and min. 0.08 MPa to EPS, with the layer-to-layer figure after ageing also at min. 0.08 MPa — the number that matters most on a wall that has already been through a few winters.
- Flexural resistance min. 5.5 N/mm² to EN 1015-11:2001+A1:2007, which is the property carrying the reinforced layer through thermal movement once the render is on.
- 90-minute pot life: a batch stays workable long enough to bond a full lift, and because the figures are declared at +23 °C and 50% relative humidity, a warm bright day shortens it and a cool one stretches it.
- Machine application is provided for: Henkel names Wagner PC 15 and SPG Baumaschinen PG 20 with a 6 mm nozzle, so a large elevation can be sprayed rather than trowelled.
- Graphite EPS is in scope: the manufacturer states the mortar can be used for graphite polystyrene and for energy-efficient construction, so a project mixing white and graphite boards keeps one adhesive.
Declared Technical Data From the Ceresit ZU Data Sheet
Every line below is transcribed from the Ceresit ZU technical data sheet published on Henkel's own datasheet host and fetched this session. Where that sheet is silent, this page is silent: it declares no colour, no basecoat thickness in millimetres and no fixing quantity per square metre.
| Property | Declared value |
|---|---|
| Base | Cementitious and lime mixture with mineral fillers and modifiers |
| Bulk density | approx. 1.3 kg/dm³ |
| Mixing ratio | 4.5–5.0 l water per 25 kg |
| Temperature of application | +5 °C to +25 °C, substrate and ambient |
| Pot life | up to 90 minutes |
| Compressive strength | 20 N/mm², class CS IV, EN 1015-11:2001+A1:2007 |
| Flexural resistance | min. 5.5 N/mm², EN 1015-11:2001+A1:2007 |
| Adhesion to concrete | min. 0.25 MPa, ETAG 004 |
| Adhesion to EPS boards | min. 0.08 MPa, ETAG 004 |
| Adhesion between layers after ageing | min. 0.08 MPa, ETAG 004 |
| Water absorption after 24 h | max. 0.5 kg/m², ETAG 004 |
| Assumed consumption — fixing boards | approx. 5.0 kg/m² |
| Assumed consumption — reinforced layer | approx. 4.0 kg/m² |
| Assumed consumption — putty layer | approx. 1.0 kg/m² |
| Shelf life | up to 12 months from production, dry and cool, on pallets in undamaged packaging |
| Packaging | 25 kg bags |
| Reference conditions for the declared data | +23 °C, 50% relative humidity |
Two figures follow straight from the table. A bag covers 25 kg ÷ 5.0 kg/m² = 5.0 m² of board fixing or 25 kg ÷ 4.0 kg/m² = 6.25 m² of reinforced layer — and the third consumption line, the 1.0 kg/m² putty layer, is the one most quantity estimates leave out.
Certification Scope — Which Assessment Covers Which System
The assessments on this sheet belong to complete Ceretherm systems, not to the bag on its own, and they differ by system. Read the row that matches the build-up actually being installed.
| Ceretherm system | Assessment | Certificate and DoP | Reaction to fire, EN 13501-1 |
|---|---|---|---|
| Popular | ETA 08/0309 | 1488-CPR-0382/Z · DoP 00426 | B–s1, d0 |
| Impactum | ETA 13/0086 | 1488-CPR-0407/Z · DoP 00436 | B–s2, d0 |
| Reno | ITB-KOT-2018/0472, edition 1 (national) | 020-UWB-0895/Z · NDoC 00444 | Not stated on this sheet |
Both fire classes are system classifications tested on an assembled wall, so neither is a property of the mortar and neither transfers to a different build-up. Taking the stricter of the two, B–s2, d0 in Ceretherm Impactum is the figure to plan against where the exact system is not yet fixed, with B–s1, d0 available where the wall is genuinely built as Ceretherm Popular.
For a UK project these are European and Polish system documents rather than UK product approvals; the sheet separately lists Irish Agrément Board Certificate No. 09/0340 as a document of reference. Under current Approved Document B guidance the external wall is assessed as a whole construction, so the certificate that counts is the one covering the finished build-up — the sequence set out in the EWI system build-up guide.
How to Apply Ceresit ZU — Mixing, Board Fixing and the Reinforced Layer
Mixing the bag
Pour the powder into a measured 4.5–5.0 litres of cool, clean water and stir with a paddle mixer to a lump-free mass, then wait about five minutes and mix again. Working through the batch inside the 90-minute pot life keeps the mortar performing as declared.
Fixing the boards
- Trowel a continuous 3–4 cm strip around the board edge plus a few spots of approximately 8 cm diameter.
- Press the board home immediately with light blows of a long float, so the pressed mortar covers a minimum of 40% of the board's surface.
- On even, smooth substrates, comb the mortar on with a 10–12 mm toothed float instead.
- Butt the boards tightly and stagger the vertical joints in the brick-like pattern the sheet specifies.
- Where the substrate is doubtful, bond 100 × 100 mm polystyrene test pieces and pull them after four to seven days: torn polystyrene means the wall is carrying, while a piece that lifts with mortar attached calls for mechanical fixings.
The reinforced layer
Once the mortar has set, sand the boards, add the mechanical fixings and spread fresh ZU with a 10 or 12 mm notched trowel. Bed Ceresit CT 325 reinforcing mesh into the wet mortar with 10 cm overlaps and smooth until the weave no longer shows; the basecoat and mesh reinforcement guide covers the embedding technique in detail, and both stocked grades sit in the fibreglass mesh range.
Installation Notes — Curing Interval, Conditions and Site Practice
One divergence is worth settling before the programme is written. The data sheet says the boards are sanded and fixed after the mortar has set in, at three days, while Henkel's own Ceresit product page says after approximately 24 hours. Plan to the longer figure, which is the stricter of the two, and treat a faster turnaround as something to confirm with the system holder for the specific job.
- Work dry, between +5 °C and +25 °C for both substrate and air, and protect the finished reinforced layer from rain — sheeted scaffolding is recommended in the sheet itself.
- Stay off sunlit walls during the reinforced layer, so the mortar does not skin before the mesh is bedded and smoothed.
- Cover the boards within two weeks: if the reinforced layer is delayed beyond that, check the board faces, and take yellowed or dusty surfaces back with coarse sandpaper before continuing.
- Fixing quantity comes from the system, not the mortar: the sheet requires mechanical anchors at the reinforced-layer stage but declares no number per square metre, and the fixing pattern and spacing guide explains how that figure is set.
- Clean tools wet: fresh splashes wash off with water, while hardened material has to come off mechanically.
Read across a whole elevation, the three-day interval is what shapes the schedule rather than the mixing or the trowelling, since it sits between board day and mesh day on every lift. The day-by-day EWI installation timeline puts that pause into a realistic UK programme.
Choosing Between ZU and the Other Bonding Routes
| Your project | Best route | Standout spec |
|---|---|---|
| Ceresit Ceretherm EPS or graphite EPS facade | Ceresit ZU 25 kg, on this page | ETA 08/0309 in Ceretherm Popular |
| Cement adhesive for a different system, or a white-cement base | EPS adhesives basecoats | Brand-matched 2-in-1 mortars |
| Fast board fixing with no mixing station | foam against cement adhesive comparison | Canister foam, board fixing only |
| Stone wool slabs on a fire-sensitive elevation | mineral wool insulation | ZU's scope is EPS and XPS only |
Is Ceresit ZU the Right Mortar for Your Build-Up?
- Yes, for a Ceretherm EPS or XPS facade: one mortar covers bonding and reinforcement, with ETAG 004 bond figures and an ETA against the system it belongs to.
- Materials cost per square metre: at £12.90 per 25 kg bag, August 2026, board fixing works out at £12.90 ÷ 5.0 m² = £2.58/m² and the reinforced layer at £12.90 ÷ 6.25 m² = £2.06/m², so both stages together come to about £4.64/m² in mortar alone, before boards, mesh, fixings and labour.
- Insulating with stone wool instead? The declared scope of Ceresit ZU mesh adhesive 25kg is EPS and XPS, so slab build-ups take a wool-rated adhesive from the mineral wool insulation range.
- Still choosing between brands? The EPS adhesive selection guide sets the Ceresit and Atlas mortars side by side on board type, system and certification.
- Ready to order: the bag was showing in stock at the August 2026 check, and Renders World holds the CT 325 mesh that the reinforced layer needs alongside it.
FAQ — Quantities, Compatibility and Compliance
How many bags does 100 m² of external wall insulation need?
Both stages are counted, using the sheet's assumed consumption:
- Board fixing: 100 × 5.0 = 500 kg ÷ 25 = 20 bags.
- Reinforced layer: 100 × 4.0 = 400 kg ÷ 25 = 16 bags.
- Total 36 bags, and a 10% site allowance for reveals, corners and offcuts takes the order to about 40 bags.
Can it be used on mineral wool boards?
No — Henkel writes the scope as EPS and XPS boards within Ceretherm, and recommends white or graphite EPS meeting EN 13163. Stone wool has different fibre structure and vapour behaviour and takes a wool-rated adhesive, which keeps both the bond and the system documentation intact.
What are the weather limits on the day?
Dry conditions with substrate and ambient temperature from +5 °C to +25 °C, no reinforced-layer work on sunlit walls, and protection from rain once the layer is on. Sheeting the scaffold keeps a marginal spring or autumn day workable and the declared figures meaningful.
Is Ceresit ZU certified for UK use?
The documented cover is European and national system assessment — ETA 08/0309 in Ceretherm Popular and ETA 13/0086 in Ceretherm Impactum, with Irish Agrément Board Certificate No. 09/0340 listed as a reference document. UK compliance is assessed on the finished external wall, so specify the mortar as part of a named system and keep the manufacturer's documents with the project file.
Does it also work as a levelling or skim coat?
The sheet carries a third consumption line, a putty layer at approximately 1.0 kg/m², alongside board fixing and the reinforced layer. That is the thin closing pass over a reinforced surface rather than a substrate levelling render, which the sheet handles separately by asking for hollows to be filled with cement render before bonding starts.
How should bags be stored on site?
Up to 12 months from the production date, kept dry and cool on pallets in undamaged packaging. The powder is alkaline once mixed because of its cement and lime content, so gloves and eye protection during mixing are sensible, and eyes that catch a splash are rinsed thoroughly with water.
Technical Documentation