Description
At 120 mm the Frontrock Super slab sits one step past the general-purpose retrofit thickness, and it is the deepest board in the range still packed three to a bundle. It belongs to the wider mineral wool insulation range at Renders World, supplied three slabs to a 1.8 m² pack.
Where This Stone Wool Board Fits on a UK Facade
Rockwool Super 120mm mineral slab is a stone wool ETICS board declaring 0.036 W/mK thermal conductivity to EN 12667 and a declared thermal resistance of 3.30 m²K/W, fixed behind render where a solid wall needs more depth than 100 mm provides.
Take that resistance from the declaration rather than from a calculator. Dividing 0.120 m by 0.036 W/mK returns 3.33, while the manufacturer declares 3.30 m²K/W at this thickness. The gap is small, and it is exactly the sort of rounding that decides whether a marginal compliance calculation passes on paper.
- Deeper solid-wall retrofit: pre-1919 brick and stone where the target asks for more than the 100 mm board delivers, kept vapour-open at μ = 1 to EN 12086.
- Framed construction behind a render carrier: a non-combustible layer where the fire strategy sets the material before the U-value does.
- Exposed and wind-driven-rain elevations: long-term water absorption declared at ≤ 3.0 kg/m² to EN 12087.
Why Specifiers Choose a Dual-Density Stone Wool Slab
- Euroclass A1 to EN 13501-1: declared for the slab under DoP RW-CEE-DoP-0237/BCM/23/w1, and declared as unchanged by heat, weathering and ageing — the class does not drift over the life of the wall.
- Declared compressive stress of 20 kPa: CS(10)20 to EN 826, so the board holds its thickness under fixing plates rather than dishing behind the render.
- Tensile strength of 10 kPa perpendicular to the faces: TR10 to EN 1607, which governs pull-off resistance once adhesive and fixings are both loaded.
- Vapour-open at μ = 1: effectively the resistance of still air, so an insulated solid wall keeps drying outward through a wet winter — the property that matters most on the older masonry this thickness usually goes onto.
- Tight thickness tolerance at class T5: to EN 823, keeping board faces flush across a run and saving base-coat material at the joints.
Declared Performance — Thermal, Fire and Moisture
| Property | Declared value | Standard |
|---|---|---|
| Thermal conductivity λD | 0.036 W/mK | EN 12667 |
| Thermal resistance RD at 120 mm | 3.30 m²K/W | EN 13162 |
| Reaction to fire | Euroclass A1 | EN 13501-1 |
| Compressive stress at 10% deformation | 20 kPa | EN 826 |
| Tensile strength perpendicular to faces | 10 kPa | EN 1607 |
| Water vapour diffusion resistance factor | μ = 1 | EN 12086 |
| Short-term water absorption | ≤ 1.0 kg/m² | EN 1609 |
| Long-term water absorption | ≤ 3.0 kg/m² | EN 12087 |
| Thickness tolerance | Class T5 | EN 823 |
| Dimensional stability | DS(70,-); DS(70,90) | EN 1604 |
Two entries on the declaration are deliberately blank, and both are worth knowing before a specification is written. Sound absorption and point load carry no declared performance, so an acoustic figure for a finished wall comes from testing that wall, not from this board. A U-value behaves the same way: it belongs to the whole build-up and never to a board, and the U-value calculation method for wall insulation thickness sets out how the layers add up.
How to Install the Slab Behind a Render System
Stone wool is fitted rather than poured, and at 120 mm the handling changes slightly — the board is deep enough that a short knife stops being the right tool.
- Set the base track level to suit the finished insulation depth, and work upward from it so the first course carries the geometry for everything above.
- Bond with a wool-compatible adhesive. Use Roker U grey adhesive for wool and EPS, formulated for stone wool fibres; the general-purpose products on the EPS adhesives basecoats shelf are matched to polystyrene instead.
- Butt the slabs tightly in a broken-bond pattern, keeping joints closed — an open joint is the one place a continuous layer stops being continuous.
- Fix mechanically with plates and plugs from the insulation fixing accessories range, to the schedule issued for the project.
- Reinforce and render once the fixings sit flush, embedding mesh fully in the base coat.
Plug length has to be re-specified when moving up from a thinner board, because the extra 20 mm of insulation comes straight out of the embedment depth. Fixing count and length are both set by the system holder's schedule and a project wind-load calculation, and Renders World holds the plate and plug range to match whichever schedule the designer issues.
Thickness Options Across the Range
| Thickness | Declared RD | Pack | When to choose it |
|---|---|---|---|
| 80 mm slab | 2.20 m²K/W | 3 slabs, 1.8 m² | Where reveal depth or projection limits the build-up |
| 100 mm slab | 2.75 m²K/W | 3 slabs, 1.8 m² | The general-purpose retrofit thickness |
| 120 mm | 3.30 m²K/W | 3 slabs, 1.8 m² | Deeper retrofit targets on solid walls |
| 160 mm slab | 4.40 m²K/W | 2 slabs, 1.2 m² | Low-energy work where depth is available |
Stepping from 100 mm to 120 mm adds 0.55 m²K/W for the same three-slab pack, and it is the last thickness before the pack drops to two slabs and 1.2 m² of coverage. Anyone comparing prices across the range should put them on a per-square-metre footing first, because the pack break at 140 mm makes a straight pack-to-pack comparison misleading.
Ordering — Pack Size, Price and Matched Components
Rockwool Super 120mm mineral slab is sold by the pack of three at £47.80 per 1.8 m² pack as displayed in August 2026. On the pack coverage above that is £47.80 ÷ 1.8 m² = £26.56 per m² for the insulation layer alone, before adhesive, fixings, mesh and finish.
- Order in pack multiples: coverage steps in 1.8 m², so a 60 m² elevation needs 60 ÷ 1.8 = 33.3, rounded up to 34 packs before any allowance for cuts at reveals and returns.
- Pallet quantity: 12 packs per pallet, covering 21.6 m² — the figure a scaffold-loading calculation needs.
- Pack weight: 16.5 kg, still a comfortable one-person lift.
Note that the pallet holds 12 packs at this thickness against 16 at 100 mm, so a delivery covering the same wall area arrives on more pallets and needs more standing room on site.
Is This the Right Slab for Your Project?
- Choose it where a non-combustible insulation layer is required and the elevation can carry 120 mm plus render without fouling reveals, eaves or a boundary.
- Step down to the 100 mm Super slab at 2.75 m²K/W when projection is tight or the calculation is already satisfied.
- Step up to the 160 mm Super slab at 4.40 m²K/W where depth is available and the target is more demanding.
- Weighing wool against polystyrene? The mineral wool and polystyrene comparison sets out where each earns its place, and the facade fire requirements briefing covers where the choice is made for you.
- Period masonry: the solid-wall Victorian retrofit guide and the condensation risk guide cover the moisture side of a deeper build-up.
FAQ — Coverage, Compatibility and Compliance
How much does one pack cover?
Three slabs at 1000 × 600 mm give 1.8 m² laid flat, the same coverage as the 80 mm and 100 mm packs. Add an allowance for cuts at reveals, returns and parapets before converting an elevation area into a pack count.
Which adhesive suits stone wool?
A wool-compatible cementitious adhesive is the requirement, since stone wool fibres bond differently from a closed-cell board face. Roker U grey is the product held for this range at Renders World.
Do fixings need to change when moving from 100 mm to 120 mm?
Yes — the additional 20 mm of board comes directly off the embedment depth, so a plug sized for a thinner slab will sit shallower in the substrate. Plug length and the number per square metre both come from the system holder's fixing schedule and the project wind-load calculation, so confirm those before ordering rather than carrying over the last job's quantities.
Does the A1 class apply to the finished wall?
Euroclass A1 to EN 13501-1 is declared for the slab under its Declaration of Performance, and declared as unchanged by ageing. A completed external wall combines several materials, so its performance is assessed as a system by the building designer under current Approved Document B guidance.
Why is the declared R-value 3.30 rather than 3.33?
The declaration publishes a rounded resistance for each thickness, and that published figure is the one a compliance calculation should carry. Dividing thickness by lambda gives a slightly higher answer and is not the declared property.
Is an acoustic improvement figure available?
Sound absorption is declared as NPD — no declared performance — across every thickness of this slab, so any acoustic benefit on a finished facade is established by testing the completed build-up rather than quoted from the board.
Technical Documentation