1 · Substrate prep

Existing soffit cleaned of dust, oil, paint, and loose material. Concrete made good where spalled. For basement soffits in older properties, hygroscopic salts and moisture history are tested before fixing. Any active condensation source on the upper floor (failed bathroom tiling, undetected slow leaks) traced and addressed before the boards go up.

2 · Xella mineral adhesive

Xella-specified mineral adhesive applied to the board face on a perimeter-and-dab pattern. The same chemistry family as the board (calcium silicate based) for compatibility — no organic adhesives that would compromise the A1 fire classification. Boards offered up to the soffit and pressed into the bed.

3 · Mechanical fixings

Polymer plug-and-pin fixings drilled through the board into the concrete or masonry above — typically 4–6 per board for overhead applications. Mechanical fixings are mandatory overhead (gravity is working against the adhesive bond) — never adhesive-only on a ceiling, even for short-span boards.

4 · Joint reinforcement

Self-adhesive mesh tape over every butt joint and at perimeter wall-to-soffit junctions. The mesh and the board face together give the painter or render coat a continuous surface — no plaster skim layer needed, no plasterboard layer needed.

5 · Surface levelling (optional)

Where the soffit will be a visible architectural ceiling (residential basement, gallery space, retail), a thin mineral reinforcing coat embeds the mesh and creates a flat paint-ready surface. For utility applications (underground car parks, plant rooms), the board face is painted direct without levelling — board joints visible but performance unaffected.

6 · Paint or mineral finish

Mineral primer (matched to the board chemistry) followed by emulsion, silicate, or mineral paint topcoat. White matt finish is the default for basements and car parks; colour options for architectural soffits. No plasterboard, no skim, no second-fix wet trade.

Autoclaved aerated concrete (AAC)

Same chemistry family as Xella's Ytong and Hebel structural AAC blocks — millions of m³ in service across European construction since the 1920s. Multipor is the thermal-insulation-grade product at lower density, made on the same plant chemistry, with the same long-term performance record.

Lime, cement, silica sand, water

Standard cementitious binders mixed with fine silica aggregate, plus a small amount of aluminium powder as the aeration agent. The aluminium reacts with the alkaline slurry during manufacture, generating hydrogen bubbles that create the foam structure. The hydrogen escapes; what remains is a fixed mineral foam.

Autoclave cure

Boards are cured under high pressure and saturated steam in a sealed autoclave. The cure forms tobermorite — a calcium silicate hydrate mineral — that gives the boards their final strength and dimensional stability. Same cure process used for AAC structural blocks; well-understood, century-old chemistry.

115 kg/m³ density

Light enough to handle and lift overhead (a 600 × 390 × 100 mm Multipor board weighs about 2.7 kg — manageable by a single fitter on a step or scaffold); dense enough to paint directly, support light fixings, and resist abrasion in a public ceiling environment.

100% inorganic mineral

No plastic content, no organic binder, no fibre reinforcement, no flame retardant. The board is calcium silicate hydrate plus aerated voids, end of bill of materials. Cradle-friendly disposal — disposes with construction rubble at end of life, no hazardous-waste designation.

Fire: A1 non-combustible

Pure mineral matrix, no organic content, no contribution to fire. Euroclass A1 — the highest non-combustibility class available. No 11 m external wall height restriction, no fire-engineering compensating measure required. The single biggest spec advantage on commercial overhead insulation work.

50+ year design life

AAC chemistry has a century of European service history in Ytong structural blocks. Multipor is the same family, manufactured at thermal-insulation density. Properly fixed and finished, the boards stay in service for the life of the building — set-and-forget overhead insulation.

No annual service required

No moving part, no electrical component, no consumable. The painted mineral ceiling is the same maintenance cycle as any painted ceiling — repaint as the homeowner's normal cycle dictates, every 10–15 years for commercial spaces.

Refinish or recolour any time

The mineral surface accepts any compatible mineral or emulsion paint system. Retail and commercial fit-outs change ceiling colour without disturbing the insulation. The same mineral primer works for repaints; no need to remove or replace boards to refresh the appearance.

Skamol on basement walls

A basement is a 5-sided thermal envelope. Multipor handles the soffit; SkamoWall (or Redstone Clima Redboard Pro) handles the walls. Both A1 mineral, both alkaline anti-mould, both vapour-open. CleverBloom usually quotes basement scope as a combined Multipor-and-SkamoWall package — fewer trades, single project handover, coordinated detailing at the wall-to-soffit junction.

Services penetrations sealed A1

A Multipor soffit only delivers its A1 fire performance if services penetrations (downlights, cable routes, pipework, ventilation ducts) are sealed with A1-rated firestop materials. Combustible foams used as quick gap-fillers around services compromise the whole assembly. CleverBloom seals every penetration with rated mineral firestop as part of the scope.

Condensation source above

Multipor stops the soffit being a cold surface, but it can't fix moisture sources in the room above. Failed shower tray seals, undetected slow plumbing leaks, or a poorly-ventilated bathroom directly over the basement will eventually saturate the boards from above. Before fitting, we check the upstairs services and ventilation; remedial work upstairs goes first.