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Inside one of the units after the work: the underside of the mezzanine deck in a continuous black finish over the closed-cell layer, cable trays and lighting below, white hygienic rooms along the left and a roller door open to the yard.
Project recordThe deck, finished

Project record · Metal deck soffit · Closed-cell, profile filled first

Food-sector units, London: 324 m² of deck soffit at 140 mm.

Two adjoining industrial units in south London, fitted out for the food sector, with a corrugated metal mezzanine deck over the working floor. We filled the profile, built 140 mm of NexSeal LE closed-cell beneath it in three passes, and checked the layer for depth at 29 points and for adhesion and cohesion, then finished it in a black vapour control coating.

324m²
Metal deck soffit treated
140mm
Closed-cell, in three passes
29
Depth checks recorded
Five days
14 to 18 September 2026

01The building

A metal deck over clean rooms, with services everywhere beneath it.

The units were being fitted out as food-sector premises: white hygienic rooms on the ground floor, a mezzanine above them, and cable tray, lighting and pipework hung beneath the deck. The underside of that deck is a corrugated metal profile on downstand beams, and it needed insulating, sealing against moisture vapour and finishing cleanly over the rooms below.

Why the deck mattered. Bare metal follows the temperature on its other side. Beneath it, warm and humid air from the rooms meets a cold surface, and every trough in the profile is a place for condensation to gather above a food area.

Why the profile came first. A corrugated deck has deep troughs between its ribs. Spraying straight to depth would bridge them and leave voids against the metal. Filling the profile first gives the build-up passes a flat, bonded base.

The brief. 140 mm of closed-cell across the deck and its beams, continuous around the services, with the conditions, the depth and the bond all recorded, then a black vapour control finish over the top.

Building
Two adjoining industrial unitsFood-sector fit-out, mezzanine over hygienic rooms
Location
South London
Substrate
Metal soffit, underside of the mezzanine deckCorrugated profile; services and cable tray below
Area
324 m²
Application
140 mm Enverge NexSeal LE closed-cellMorrells Mako 2K Etch Primer on the prepared metal
Finish
Bostik Idenden ET-150 vapour control coating, black
Conditions
Deck dry, clean and fixedSubstrate 23°C against a dew point of 15°C
Verification
Depth at 29 points; adhesion and cohesion

02What we specified, and why

Primed metal, 140 mm of closed-cell on a filled profile, and a black vapour control coat.

The depth was set at 140 mm. The method made sure that depth was a continuous bonded layer across the ribs, the troughs and the beams, rather than a skin over hidden voids, and the coating sealed and finished it.

  • The base: Morrells Mako 2K Etch Primer. Applied to the agreed areas of metal before any foam, giving the insulation a properly prepared surface to bond to.
  • The system: Enverge NexSeal LE closed-cell, at 140 mm. Sprayed directly to the underside of the metal deck, bonding to the profile and closing around beams, hangers and fixings. λ 0.027 W/mK is the product's declared figure. Profiled metal roof underside, the application.
  • Why the profile is filled first. The troughs were filled before the build-up began, so each following pass sat on a level, bonded surface and nothing was left hollow against the metal.
  • Why three passes. 50, 50 and 40 mm, with 12 minutes between them. Closed-cell foam gives off heat as it cures; controlled passes keep each layer stable and bonded to the one beneath.
  • The finish: Bostik Idenden ET-150 vapour control coating, in black. Applied over the cured foam to form a vapour control layer. It reduces moisture vapour moving from the warm, humid rooms into the insulation, supports condensation control, and leaves a clean, durable surface over the services.
Product
Enverge NexSeal LE, closed-cell
Depth
140 mm, passes of 50, 50 and 40 mm
Primer
Morrells Mako 2K Etch Primer, prepared metal
Density
38 kg/m³, checked on site
Coating
Bostik Idenden ET-150 vapour control, black
Checks
Depth at 29 points, adhesion, cohesion
The underside of the mezzanine deck after the work: the deck and a downstand beam under one continuous layer in a black finish, hangers and cable tray running below, the tops of the white rooms beneath.

Over the beams. The deck and its downstand beams under one continuous layer, finished in the black vapour control coat. Project record.

Footage and photographs · Project record

The layer going on, the depth gauged, the deck coated.

Beneath the deck with the foam on and the black coat starting, one of the 29 depth checks, the Bostik black coat over the services, and the finished soffit above the rooms.

Project recordDuring: foam on
A depth gauge pushed into the cured closed-cell layer on the underside of the deck.
Project recordChecked: depth gauge
After: the Bostik Idenden ET-150 vapour control coating in black over the foam, above mesh cable tray and strip lights, a roller door at the right.
Project recordAfter: Bostik black coat on
After: the finished soffit above the white hygienic rooms, with cable tray, lighting and a steel column.
Project recordAfter: above the rooms

Footage and photographs from the job, as it ran. Labelled Project record because they are.All project records

03How the work ran

Prime, log the conditions, fill, build up, check, coat.

A fit-out in progress, with rooms already built beneath the deck. The sequence protected what was below, confirmed the metal was fit to spray, and recorded the result before the coating sealed it.

  1. Preparation

    Deck primed, services and rooms protected.

    The deck confirmed dry, clean and fixed; Morrells Mako 2K Etch Primer applied to the agreed areas of prepared metal; cable tray, lighting and the rooms below sheeted before spraying.

  2. Conditions

    Logged before the first pass.

    25°C ambient and 55% relative humidity, with the deck at 23°C against a dew point of 15°C: 8°C of margin, so the metal stayed dry as the foam went on.

  3. Application

    Profile filled, then three passes to 140 mm.

    The troughs filled first, then passes of 50, 50 and 40 mm with 12 minutes between them, and the spray zone ventilated for an hour. Five sets across the five days.

  4. Checks and finish

    Checked and signed, then coated in black.

    Density checked at 38 kg/m³, adhesion and cohesion passed, and the depth gauged at 29 points; signed by the lead installer and the site supervisor on 18 September 2026. Bostik Idenden ET-150 then applied over the cured foam.

04The outcome

A continuous 140 mm layer across the deck, checked, then sealed in black.

The figures are the site's own: the depth gauged on the cured foam, the bond tested on the deck, the dates from the daily log.

Depth

140mmas specified

Gauged at 29 points across the deck, each at about 140 mm.

Coverage

324m²continuous

One layer across ribs, troughs and beams, the profile filled before the build-up.

Bond

Passadhesion and cohesion

Tested on the deck after application, with density checked at 38 kg/m³.

Finish

Coatedvapour control, black

Bostik Idenden ET-150 over the cured foam: a vapour control layer and a clean, durable surface.

Where this record comes from

The job's own quality record. The daily spray foam log: conditions, processing settings, site tests and a photographic register of 37 points, signed on completion. The coating is recorded separately, as its own stage.

Yours will differ. A different deck, objective or exposure gives a different depth. How thickness follows the objective.

05Where this record leads

If this looks like your building.

The application this record used, the building family, and how the depth is set. More work in and around London: spray foam insulation London.

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