Description
Ceresit CT 84 Express XPS is an XPS adhesive in foam form: a one-component, low-expansion polyurethane, applied with a gun, that bonds extruded polystyrene boards to foundation walls and the plinth zone. It sits with the other board adhesives and basecoats, and its work stops where the facade starts — boards above the plinth, in EPS or mineral wool, take a different CT 84.
XPS Adhesive for Foundation Walls and the Plinth Zone
Ceresit gives this foam one main job: fixing XPS insulation boards to the foundation walls of a building. The Czech edition of the technical sheet widens that slightly. It covers the whole substructure and plinth zone, and it also covers repair work on an existing plinth where boards have come loose from the wall.
- Foundation and plinth insulation in XPS — the use every edition of the sheet names first.
- Loose XPS boards on an existing plinth — pierce the board through to the wall and inject the adhesive at the spacing the repair needs; thin boards are held flat locally so they do not bulge.
- Layered bonding of polystyrene boards, in normal and in reduced temperatures.
The substrate list is long, and it reads like a foundation wall rather than a facade: ceramic brick, concrete, aerated concrete dry or after water exposure, timber, OSB, coated and galvanised steel sheet, glass, bitumen and plasterboard. The Czech edition adds fibre-cement and gypsum-fibre boards, dry masonry and bituminous waterproofing membranes. Bitumen matters most here, because a foundation wall below ground often already carries a bituminous damp-proofing coat before any insulation goes on.
One exclusion is stated plainly: smooth plastic films — plasticised PVC, polypropylene, polyethylene and PTFE — are not recommended as a substrate. On anything similar, bond a trial board and test it before committing the wall.
Technical Data — CT 84 Express XPS
| Property | Declared value |
|---|---|
| Product type | One-component, low-expansion polyurethane adhesive |
| Boards | Extruded polystyrene (XPS) |
| Yield per container | Up to 14 m² on foundation insulation, 2 cm bead |
| Air and substrate temperature | +5 °C to +35 °C |
| Air humidity | Even above 90 % |
| Hardening time | Approx. 2 hours |
| Anchors | From approx. 2 hours after bonding |
| Surface correction | Up to 20 minutes after bonding |
| Thermal conductivity | λ 0.040 W/(m·K) |
| Bond, XPS to concrete, 8 mm joint | ≥ 0.08 MPa at 0 °C and at +40 °C / 30 % RH |
| Container | 750 ml metal can |
| Shelf life | 15 months from the production date on the base |
| Storage | Upright, cool and dry, +5 °C to +50 °C, no frost |
| Reference conditions | +23 °C, 50 % relative humidity |
The bond figure comes from Henkel's Polish national declaration of performance No. 00556, which covers CT 84 Express XPS together with five other adhesives of the CT 84 family; every other line is printed on the technical sheets. The 14 m² is a ceiling, not an average: the manufacturer measures it on a 2 cm bead and states that the real yield moves with temperature, humidity, the gap between board and wall, and the way the adhesive is laid.
The two editions of the sheet agree on every working figure and part on one: storage. The Polish edition asks only for a temperature above zero; the Czech edition sets +5 °C to +50 °C and adds protection from frost and direct sun. Store to the tighter range — a van left out overnight in January can fall below it.
How to Apply CT 84 Express XPS on a Foundation Wall
- Prepare the wall. Before any XPS adhesive goes on, remove dust, grease and anything that weakens adhesion. Hollow-sounding plaster comes off; dirt, release-agent residue, vapour-tight paint and weakly bonded coatings come off completely, for example with a pressure washer. Brush out moss and algae, treat the area with a fungicidal wash, then let the wall dry out fully. In cold weather the surface must carry no frost, ice or snow.
- Test an existing finish. Where the wall is plastered or painted, bond 10 × 10 × 10 cm polystyrene cubes in several places and pull them off by hand after 2 to 4 hours. The wall is sound when the polystyrene tears rather than the bond or the substrate.
- Dampen the surface. The Czech edition recommends misting the substrate with clean water before application, for better adhesion and a more even cure.
- Prepare the can. Bring it to room temperature, about 15 °C, and shake it hard. Take off the valve guard, hold the can valve-up and screw the dispensing gun on with the gun's own valve closed, then open the gun valve.
- Fix the starter track first. The base profile is mechanically fixed before the first board goes on.
- Lay five vertical strips parallel to the shorter sides of the board, about 2 cm in from the edge, with the gun held can-up and a steady distance kept between gun and board.
- Place and press. Two to four minutes after laying the adhesive, set the board against the wall and press it lightly with a long straightedge. Board alignment can still be corrected with the straightedge for up to 20 minutes.
- Anchor and reinforce. From about two hours, anchors can go in. Roughen the smooth face of the XPS before the reinforcing layer, which is built with a cement basecoat and glass-fibre mesh; the Czech sheet names Ceresit CT 325 glass-fibre mesh for it.
Where the anchors, spacing and board layout are still open, the guide to fixing pattern and spacing covers them, and the basecoat and mesh reinforcement guide takes the next layer from there.
Weather, humidity and the working window
Work between +5 °C and +35 °C, air and substrate alike. High air humidity speeds the setting of the foam rather than stopping it, and the Czech edition recommends the adhesive precisely for poorer weather, when cement adhesives dry slowly or not at all. In strong wind or rain, scaffold nets or sheeting are required, with extra attention to the corners of the building. The weather window planning guide sets these limits against the UK calendar.
Why a Foam XPS Adhesive at the Plinth
- Anchors on the same day. With a foam XPS adhesive the insulation can be anchored from about two hours after bonding, so a plinth run bonded in the morning is anchored in the afternoon.
- A bond line that insulates. Ceresit declares a thermal conductivity of 0.040 W/(m·K) and describes the cured foam as close to polystyrene or wool in thermal behaviour, which a cement adhesive is not.
- Damp is not the enemy. The adhesive works in air humidity above 90 %, and moisture speeds its cure — useful at ground level, where the wall rarely dries out completely.
- One can across the awkward substrates. Bitumen, concrete, brick and sheet materials all appear on the same list, so a foundation wall that changes material along its length is bonded with one XPS adhesive.
For the choice of board itself, the comparison of extruded and expanded polystyrene sets the two materials side by side, and the plinth thermal bridge guide explains why the detail at the base of the wall decides how the whole insulation performs. Against a bag of cement adhesive, the foam and cement adhesive comparison weighs the two workflows.
CT 84 Express XPS or the EPS and Wool Version
| Question | CT 84 Express XPS | CT 84 Express Plus |
|---|---|---|
| Boards the manufacturer names | Extruded polystyrene (XPS) | EPS and mineral wool |
| Where it goes | Foundation walls and plinth zone | Facade insulation systems (ETICS) |
Above the plinth, the boards change and so does the adhesive: the CT 84 version for EPS and mineral wool facades takes over there. How the two zones fit into one wall is laid out in the EWI build-up guide.
What the Adhesive Needs Around It
- A PU foam dispensing gun. This XPS adhesive is applied through a gun screwed onto the can; the technical sheets describe no other method.
- Starter tracks and anchors from the fixings and accessories range — the track goes on before the first board, the anchors after about two hours.
- A filling foam for the joints. Ceresit recommends a polyurethane gap-filling foam, not the adhesive, for any gaps between XPS boards, because it insulates better.
- Acetone or a PU foam cleaner for fresh adhesive on tools and surfaces; once cured, it comes off only mechanically.
Ordering for a Plinth Run
Each 750 ml can of this XPS adhesive covers up to 14 m² of foundation insulation. A 30 m² plinth works out at 30 ÷ 14 = 2.1 cans, so order three: the 14 m² is the manufacturer's upper figure, and a rough wall, a wider gap or cold weather all bring it down.
- Dispatch: Renders World processes orders the same day when the stock is there.
- Delivery: not calculated at checkout — the team contacts you after the order with the most cost-effective option, and every delivery is kerbside.
- Collection: in person from the Renders World counter in Southampton during opening hours. Carry the cans in the load space of the vehicle, never in the passenger cabin, and keep them out of direct sun and away from anything above +50 °C, because the can is under pressure.
A can bought directly from Renders World and returned in its original condition falls within the 14-day change-of-mind return.
FAQ — CT 84 Express XPS
How many cans do I need for a plinth?
Divide the plinth area by 14 m² and round up: 20 m² needs two cans, 45 m² needs four. The 14 m² is measured on a 2 cm bead in good conditions, so a cold day or an uneven wall pushes the real figure lower.
Can I use it for EPS or mineral wool on the facade?
It is made and documented as an XPS adhesive for the foundation and plinth. For EPS and mineral wool boards on the facade, the CT 84 version for those boards is the documented choice; the national declaration covers both products, but the technical sheets give them different jobs.
What is the lowest temperature I can work at?
+5 °C, for the air and for the wall. Humidity is not a limit — the foam works in air above 90 % humidity and cures faster in it — but frost, ice or snow on the substrate is.
Will it bond to a bitumen-coated foundation wall?
Yes. Bitumen is on the substrate list of every edition of the technical sheet. The coating itself must be sound and well bonded to the wall; a loose or flaking layer is removed first, like any other weak finish.
When can the anchors go in?
From about two hours after the board is bonded. Before the reinforcing layer, roughen the smooth face of the XPS so the basecoat has something to key into.
Does the adhesive carry a fire classification?
The technical sheets and the national declaration give no reaction-to-fire class for the adhesive on its own. The Polish sheet lists European Technical Assessments for complete Ceresit Ceretherm systems, and any fire classification belongs to the complete system as tested, not to one component taken out of it.
Technical Documentation