Description
Ceresit CT84 XPS Foam 850 ml — Polyurethane Adhesive for XPS Insulation Boards
Product Overview
Ceresit CT84 XPS Foam 850 ml is a one-component polyurethane adhesive engineered for bonding extruded polystyrene insulation boards within Ceresit Ceretherm ETICS facade and foundation systems. A single 850 ml canister covers approximately 10 m² on facade applications and up to 14 m² on foundation insulation, delivering significantly higher coverage per unit than traditional cement-based adhesives at a fraction of the weight. Boards reach initial anchorage strength in approximately two hours, allowing mechanical fixings, reinforcing mesh, and basecoat work to follow the same day — a scheduling advantage that can shorten overall insulation programmes by up to five working days. Formulated for application from −10 °C to +40 °C and at humidity levels up to 100%, CT84 XPS Foam keeps installations moving through the colder, damper months of the UK building season when cementitious adhesives slow dramatically or become impractical. This product is part of the EPS adhesives and basecoats collection at Renders World, with XPS-specific formulation optimised for the closed-cell surface of extruded polystyrene boards.
Key Benefits
- High coverage from a single canister — one 850 ml can bonds approximately 10 m² on facades and 14 m² on foundation walls, meaning fewer units per project, less material handling on scaffold, and lower storage requirements on site compared with 25 kg bags of cement adhesive.
- Two-hour anchorage for same-day progression — boards are ready for mechanical fixing and reinforcing-layer application approximately two hours after bonding at +20 °C, keeping multi-trade programmes moving without overnight curing delays.
- All-season application from −10 °C — the polyurethane chemistry cures reliably at sub-zero temperatures where cementitious adhesives cannot be used, extending the UK installation season through autumn, winter, and early spring without weather-related downtime.
- Humidity tolerance up to 100% RH — moisture accelerates the polyurethane curing reaction, so damp and misty conditions that would compromise traditional adhesives work in this product's favour on exposed UK sites.
- Near-zero additional dead load at 100 g/m² — compared with approximately 5 kg/m² for a cement adhesive, the minimal bond-line weight protects the integrity of lightweight XPS boards and timber-frame substrates.
- Thermal bridging prevention — the cured polyurethane has a thermal conductivity of 0.040 W/mK, comparable to the insulation boards themselves, maintaining a continuous thermal envelope at every bond line rather than introducing a conductive path.
- Broad substrate compatibility — adhesion of ≥ 0.08 MPa (ETAG 004) verified on concrete, ceramic brick, aerated concrete, OSB, coated and galvanised steel, XPS, EPS, bituminous coatings, plasterboard, and wood.
Technical Specifications
| Property | Value |
|---|---|
| Composition | One-component polyisocyanate with propane/isobutane propellant |
| Pack size | 850 ml metal canister |
| Coverage — facade | Approx. 10 m² per canister |
| Coverage — foundation | Approx. 14 m² per canister |
| Application temperature | −10 °C to +40 °C |
| Humidity tolerance | Up to 100% RH |
| Crust formation time | Approx. 10 min at +20 °C / 60% RH |
| Hardening time (anchorage) | Approx. 2 hours at +20 °C / 60% RH |
| Thermal conductivity | 0.040 W/mK |
| Adhesion — all tested substrates (ETAG 004) | ≥ 0.08 MPa |
| Open time (levelling window) | Approx. 20 min |
| Fire classification (EN 13501-1) | B–s1,d0 |
| Frost resistance post-cure | Tolerates sub-zero temperatures 8 hours after application |
| Application method | PU gun or applicator straw, canister valve-down |
| BBA Certificate | 14/5142 |
| Shelf life | 15 months from production date (store above +5 °C) |
Application and Compatibility
Ceresit CT84 XPS Foam is designed to pair with XPS insulation boards in Ceresit Ceretherm external thermal insulation composite systems. The polyurethane adhesive bonds XPS panels to new-build masonry and renovation substrates, including older render and plaster surfaces confirmed as load-bearing. The closed-cell surface structure of XPS boards requires an adhesive that develops mechanical grip without relying on moisture absorption into the board face — the polyurethane formulation achieves this by expanding slightly during cure to fill micro-irregularities and create a continuous bond line.
For facade insulation, apply a perimeter bead 20 mm from the board edge and one central bead parallel to the long side. Press the board to the wall with a long float two to four minutes after application and level within the 20-minute open window. For foundation and plinth insulation, apply five vertical beads parallel to the short edge of the board, 20 mm from the perimeter, providing maximum contact area where ground moisture and hydrostatic pressure demand the strongest bond. CT84 XPS Foam also bonds directly to existing insulation layers, enabling ETICS-on-ETICS upgrades without full strip-back — a practical route for Part L compliance improvements on properties with ageing insulation systems.
Installation Notes
For the cleanest result, shake the canister vigorously for several seconds before attaching it valve-down to a PU applicator gun. A gun adapter provides finer bead control and less product waste than the supplied applicator straw, particularly on longer runs. Maintain a consistent nozzle-to-board distance to ensure even bead width across the panel. Boards reach anchorage strength in approximately two hours at +20 °C; at lower temperatures the cure extends — at 3–5 °C, allow closer to three hours before proceeding with mechanical fixings.
A step worth getting right is the substrate bond test: adhesive-fix a 100 × 100 mm test piece of XPS in several locations and pull-test after two to four hours. The bond is satisfactory when the XPS board itself tears rather than the adhesive separating from the substrate. Clean unhardened adhesive residue with Ceresit PU Cleaner or acetone promptly — once cured, removal is mechanical only. On exposed scaffold lifts, protect freshly bonded boards from direct wind to maintain consistent curing. For a detailed comparison of polyurethane foam and cement-based bonding methods, the foam adhesive vs traditional adhesive guide covers performance differences across all key criteria.
Installer's Note
CT84 XPS Foam is the product that makes foundation insulation straightforward. XPS boards below the DPC are bonded directly to the foundation wall, often against damp concrete or bituminous tanking — conditions where a cement adhesive would struggle to develop any meaningful bond. The polyurethane grips immediately, the moisture actually accelerates the cure, and the boards are solid enough to backfill against within a few hours. On facade work the coverage is the standout advantage: at 10 m² per canister, a single pallet of XPS goes on in a fraction of the time it would take with bucket-mixed cement adhesive, and the scaffold stays cleaner without mixing stations and residue. Keep canisters stored above 5 °C overnight — cold canisters dispense unevenly and waste product on the first few metres of bead until the contents warm up.
Is This Product Right for Your Project?
- Ideal for XPS board bonding on facades and foundations — choose Ceresit CT84 XPS Foam when bonding extruded polystyrene boards within a Ceresit Ceretherm ETICS system, particularly on foundation walls, below-DPC applications, and cold-weather installations where polyurethane chemistry outperforms cementitious alternatives.
- For EPS board bonding instead — the Ceresit CT84 EPS Foam 850 ml in the same polyurethane range is optimised for expanded polystyrene boards and delivers the same two-hour anchorage and all-season application benefits.
- For a cement-based universal adhesive — the Roker U Grey Adhesive 25 kg offers a traditional trowel-applied bond suitable for both mineral wool and EPS boards, with a familiar workflow preferred on some specification-driven contracts where cementitious adhesives are mandated.
- For full XPS board selection — browse the XPS insulation boards collection to match the correct board thickness and lambda to your foundation or facade specification.
Frequently Asked Questions
How many canisters do I need for a typical foundation insulation project?
At approximately 14 m² coverage per canister on foundation applications, a typical semi-detached perimeter foundation of 30–35 m² requires three canisters with a comfortable working margin. Order one additional canister per project to cover bead corrections, test patches, and any gap-filling between boards without delaying the programme.
What is the difference between CT84 XPS Foam and CT84 EPS Foam?
Both products share the same polyurethane base chemistry, coverage rates, and curing characteristics. The XPS variant is specifically formulated to develop reliable adhesion on the smooth, closed-cell surface of extruded polystyrene, which is less absorptive than the open-cell structure of expanded polystyrene. In practice, either variant bonds to both board types, but specifying the XPS-labelled product ensures the adhesive-to-board interface is optimised for the substrate it will encounter most frequently on XPS-dominant projects.
Can I use CT84 XPS Foam to bond mineral wool slabs?
The Ceresit CT84 Express Plus formulation is tested and approved for fixing mineral wool boards as well as EPS and XPS within Ceretherm systems. Adhesion to mineral wool meets the same ≥ 0.08 MPa threshold (ETAG 004). For projects primarily using mineral wool, confirm with the system specification that a polyurethane adhesive is permitted — some system certifications mandate a cementitious basecoat adhesive for mineral wool boards.
Is this adhesive suitable for below-DPC and buried applications?
Yes. CT84 XPS Foam is widely used for foundation and below-DPC insulation where XPS boards are bonded to basement walls, foundation concrete, and bituminous tanking membranes. The polyurethane bond tolerates permanent ground-contact moisture and the cured adhesive does not degrade in damp conditions. Apply five vertical beads per board to maximise contact area on foundation substrates, and allow boards to reach full anchorage before backfilling against them.
Technical Documentation