Description
Ceresit CT84 XPS Foam 850 ml is the polyurethane adhesive engineered for extruded polystyrene insulation — bonding XPS boards to foundation walls, plinth zones, and below-DPC substrates at approximately 14 m² yield per canister, with cure tolerance from −10 °C to +40 °C and humidity up to 100 % RH actively accelerating the polyurethane reaction rather than compromising it.
This product sits within the professional EPS adhesives and basecoats range at Renders World and bonds XPS insulation boards at the ground-line interface where standard cement adhesives struggle with damp concrete, bituminous tanking, and cold-weather application.
Where Ceresit CT84 XPS Foam Performs Best — Plinth, DPC and Foundation Zones
Ceresit CT84 XPS Foam is a one-component polyurethane adhesive engineered for the closed-cell surface of extruded polystyrene boards, applied across the ground-line zones where XPS is mandated and standard cement adhesives cannot deliver a reliable bond on damp or bituminous substrates.
- Plinth strips between DPC and ground level — the 300–500 mm transition zone where wool or EPS field insulation steps down to denser water-resistant XPS at ground contact.
- Below-DPC perimeter insulation against foundation walls — concrete that is rarely fully dry and often coated with bituminous DPM, where the moisture is cure-accelerating rather than cure-defeating.
- Basement and cellar wall insulation against damp concrete — interior or exterior, with hydrostatic pressure on the bond line that the polyurethane reaction is built to tolerate.
- Bituminous tanking interfaces — substrates where any cement adhesive would simply not bond reliably, and where the foam chemistry is the only practical adhesive specification.
Why Trade Specifiers Choose Ceresit CT84 XPS Foam
- 14 m² foundation yield per 850 ml canister — higher coverage than the 10 m² facade rate, reflecting the closer-spaced 5-bead pattern that ground-contact bonding uses; three canisters cover a typical 30–35 m² semi-detached perimeter foundation with margin.
- Application and cure to −10 °C — the polyurethane chemistry cures reliably at sub-zero substrate temperatures where cement adhesives are unusable, extending foundation work through UK winter months.
- Humidity to 100 % RH accelerates rather than compromises cure — damp concrete, freshly tanked bituminous surfaces, and below-DPC zones become the conditions where the foam chemistry outperforms cement bonding rather than the conditions that defeat it.
- ≥ 0.08 MPa adhesion to bituminous and damp substrates (ETAG 004) — verified bond strength across concrete, brick, aerated concrete, OSB, galvanised steel, XPS, EPS, bituminous coatings, plasterboard, and wood.
- Same-day backfill at 2 hours — boards reach mechanical-fixing anchorage in approximately 2 hours at +20 °C and tolerate sub-zero exposure after 8 hours, so foundation work can be backfilled the same working day.
- λ 0.040 W/mK matches XPS — the cured foam carries the same thermal conductivity as the board it bonds, eliminating the cold-bridge lines at every bead that cement dabs create at the plinth.
- BBA 14/5142 certified — independent UK certification supports specification on projects subject to Building Control verification and warranty provider documentation.
Technical Specifications — Ceresit CT84 XPS Foam Data
| Property | Value |
|---|---|
| Product type | One-component polyurethane (PU) foam adhesive, gun-applied |
| Composition | Polyisocyanate base with propane/isobutane propellant |
| Pack size | 850 ml metal canister |
| Coverage — facade application | ≈ 10 m² per canister |
| Coverage — foundation application | ≈ 14 m² per canister |
| Application temperature | −10 °C to +40 °C |
| Humidity tolerance | Up to 100 % RH |
| Crust formation | ≈ 10 minutes at +20 °C / 60 % RH |
| Time to mechanical fixing | ≈ 2 hours at +20 °C (≈ 3 hours at 3–5 °C) |
| Open time | ≈ 20 minutes |
| Frost resistance after application | Tolerates sub-zero exposure 8 hours after application |
| Adhesion (ETAG 004) | ≥ 0.08 MPa across tested substrates |
| Thermal conductivity (λ) | 0.040 W/mK |
| Fire classification (EN 13501-1) | B–s1,d0 |
| Certification | BBA 14/5142 · Ceresit Ceretherm system |
| Shelf life | 15 months from production date, stored above +5 °C |
The foundation coverage rate is the figure that drives ordering on ground-line work. At 14 m² per canister against the 10 m² facade figure, the closer-spaced bead pattern uses more adhesive per board but delivers the bond density that backfill loading and hydrostatic pressure require.
How to Apply Ceresit CT84 XPS Foam — 5-Bead Foundation Pattern and Cold-Substrate Cure
Shake the canister vigorously for around 30 seconds, screw it valve-down into a professional PU applicator gun, and trigger a short test bead onto waste material to clear the nozzle. Two bead patterns cover the application set — facade pattern at 10 m² yield and foundation pattern at 14 m² yield — and the choice depends on the substrate, not the board type.
- Facade XPS bead pattern — one perimeter bead 20 mm from the board edge plus one central bead running parallel to the long side; press the board within 2–4 minutes and slide it into final position within the 20-minute open window.
- Foundation and below-DPC bead pattern — 5 vertical beads parallel to the short edge of the board, 20 mm from the perimeter, distributed evenly across the board width; the closer pattern maximises contact area where ground moisture and backfill loading demand the strongest bond.
- Cold-substrate timing — boards reach mechanical-fixing anchorage in approximately 2 hours at +20 °C; at substrate temperatures of 3–5 °C, allow closer to 3 hours before pinning or backfilling.
Once boards are anchored, the elevation is ready for the reinforced basecoat on facade work, or for backfilling against on foundation installations. For the foam-vs-cement decision in detail across both substrate types, the foam adhesive vs traditional cement comparison covers cost-per-m², programme implications, and substrate tolerance side by side.
Installation Notes — Bond Testing, Cold Canister Storage, Foundation Backfill
The substrate bond test is the discipline that separates a confident foundation specification from a hopeful one. Adhesive-fix a 100 × 100 mm test piece of XPS in several locations across the elevation, pull-test after 2–4 hours, and confirm the XPS board itself tears rather than the adhesive separating from the substrate. A clean separation at the bond line is the warning sign that demands a substrate primer or alternative adhesive specification before the field boards go on.
On cold foundation work, store canisters indoors above +5 °C overnight and bring them out only as the day's work demands. A canister stored in a cold van dispenses unevenly and wastes the first metre of bead until the contents reach working temperature, which on a 30 m² perimeter foundation can mean half a canister's yield lost before lunch. Clean uncured foam residue with Ceresit PU Cleaner or acetone promptly; once cured, removal is mechanical only and difficult on visible elevations.
On below-DPC zones, allow boards to reach full 2-hour anchorage before backfilling against them. The polyurethane is strong enough to hold lateral soil pressure within the working day, but compressing a partially cured bond line risks dislodging the board before the foam has fully set.
Pro Tips From UK Installers Using Ceresit CT84 XPS Foam
Foundation and plinth work is where the difference between a careful adhesive specification and a hopeful one shows up most clearly — usually six months later, when a marginal bond gives up under the first wet winter. A few site practices keep the foundation course working as intended.
- Test before you trust the substrate — bituminous tanking varies enormously between manufacturers and ages; a 4-hour test patch on every foundation specification is worth ten minutes of operative time to avoid a board-bond failure that only shows up after backfill. The torn-XPS-not-clean-separation rule is the only acceptable result.
- Bead toward the back of the cavity on plinth work — position beads slightly toward the rear face so foam expansion fills the cold-bridge gap behind the board rather than squeezing out at the visible edge; this eliminates the cold spot that causes the surface mould the homeowner notices first.
- Match canister count to perimeter, not area — a typical UK semi has 30–35 m of foundation perimeter, not 30–35 m² of elevation area; three canisters at 14 m² yield assumes the perimeter is measured correctly, and a fourth canister staged ready avoids a mid-elevation pause for resupply.
- Schedule plinth work before scaffold strike — foundation bonding is often left to the end of an EWI programme when scaffolding is being struck and access becomes awkward; schedule it at the start of the ground-floor lift instead, while operatives have full ground-level access and the substrate is still clean from site preparation.
Is Ceresit CT84 XPS Foam Right for Your Project?
- Ideal for XPS at plinth, DPC, foundation perimeter, and below-grade zones — choose CT84 XPS Foam where the substrate carries damp, bituminous tanking, or sub-zero conditions that rule out conventional cement adhesives, and where the board specification is closed-cell extruded polystyrene.
- For EPS field elevations above the plinth — the CT84 EPS Foam sibling at the same 850 ml pack delivers identical 2-hour anchorage and cold-cure performance, optimised for the open-cell surface of standard EPS; pair the two products across the elevation for a fully foam-bonded build-up.
- For cement-based universal adhesive on warranty-mandated systems — Atlas Roker U Grey 25 kg handles XPS, EPS, and mineral wool from a single cementitious product where certified systems require cement bonding.
- For deeper context on the thermal-bridge physics — the plinth thermal bridges and mould prevention guide sets out why cold-bridge management at the ground line drives the mould prevention case that XPS plus foam adhesive is designed to solve.
FAQ — Ceresit CT84 XPS Foam Coverage, Compatibility, Foundation Specification
How many canisters does a typical UK foundation insulation project need?
At the rated foundation yield of approximately 14 m² per canister using the 5-bead pattern, a typical 30–35 m² semi-detached perimeter foundation consumes three canisters with working margin. Order four per project — the extra canister covers test patches, bead corrections, gap-filling between boards, and the inevitable cold-canister yield loss on the first run of the day. On detached properties or larger commercial perimeters, scale up by 14 m² per canister and add a 15–20 % allowance for cold-weather contingency.
When should I specify CT84 XPS Foam over the standard CT84 EPS Foam?
Choose the XPS-labelled product whenever XPS boards are the substrate the adhesive will encounter most frequently — plinth strips, foundation perimeter, below-DPC zones, basement walls. The two products share the same polyurethane base chemistry and either will bond to either board type, but the XPS variant is formulated specifically for the smooth, closed-cell surface of extruded polystyrene where reliable bond development matters most. On EPS-dominant facade work, the standard CT84 sibling is the matching specification, and the XPS vs EPS comparison covers where each board type is mandated across UK EWI specifications.
Is this adhesive truly suitable for permanent below-DPC and buried applications?
Yes. The polyurethane bond tolerates permanent ground-contact moisture, and the cured adhesive does not degrade in damp conditions, which is why the product is widely specified for foundation, basement, and below-DPC insulation. Apply the 5-vertical-bead foundation pattern rather than the facade pattern, allow boards to reach full 2-hour anchorage before backfilling against them, and the bond carries the lateral soil load and hydrostatic pressure of a typical UK foundation envelope.
Can CT84 XPS Foam bond mineral wool slabs?
The Ceresit CT84 Express Plus variant is certified for mineral wool as well as EPS and XPS within Ceretherm systems, meeting the same ≥ 0.08 MPa adhesion threshold per ETAG 004. On projects primarily using mineral wool, confirm the system specification permits polyurethane bonding — some certified systems mandate cementitious adhesive for wool. The EPS adhesive and basecoat selection guide covers the cement-based wool-rated alternatives within the range.
Can I apply CT84 XPS Foam at sub-zero substrate temperatures?
Yes. The documented application range extends down to −10 °C substrate and ambient temperature, which is the lowest cold-cure rating of any adhesive in the EPS adhesives and basecoats range. The cure rate slows below +20 °C, so allow approximately 3 hours to mechanical-fixing anchorage at 3–5 °C rather than the 2-hour figure quoted at room temperature, and keep canisters stored above +5 °C overnight to maintain dispensing consistency on the first run of the day.
How should canisters be stored and disposed of on a UK foundation project?
Store canisters upright above +5 °C and below +30 °C, away from direct sunlight and frost — bring them indoors overnight on winter foundation jobs so they dispense at full yield in the morning. Shelf life is 15 months from production date in sealed canisters. Spent canisters are pressurised metal waste collected separately by the site waste carrier for licensed recycling, and the transport weight saving versus the equivalent cement bag quantity lowers the delivery carbon footprint on every below-grade project.
Technical Documentation — Ceresit CT84 TDS and BBA References