Knauf Rocksilk RS45 Acoustic Mineral Wool is a high-density rock mineral wool insulation slab used in acoustic, thermal and fire protection applications. It is suitable for use within walls, floors, ceilings, partitions, joist voids and soundproofing systems where cavity absorption is required.
This variable product is available in 50mm, 75mm and 100mm thicknesses, allowing you to choose the correct depth for your wall, ceiling or floor build-up.
Knauf Rocksilk RS45 is used to absorb sound energy within cavities and improve the performance of complete acoustic systems. It is commonly installed between timber studs, metal studs, ceiling joists, floor joists and within voids behind acoustic plasterboard systems.
It is not a standalone soundproofing barrier. Instead, it works by reducing cavity resonance and supporting the overall acoustic build-up when used with suitable boards, resilient systems, acoustic sealant and correct detailing.
Rocksilk RS45 helps improve acoustic performance by absorbing sound energy inside cavities. In a wall or ceiling system, empty voids can allow sound to resonate and pass through more easily. Filling those voids with mineral wool helps reduce this resonance.
For best results, Rocksilk RS45 should be combined with other soundproofing materials such as acoustic plasterboard, resilient bars, Genie Clips, MuteClips, acoustic membranes, acoustic sealant and perimeter isolation details.
Knauf Rocksilk RS45 can be used in a range of acoustic and insulation applications, including:
Knauf Rocksilk RS45 is a versatile mineral wool slab that can be used across multiple building applications. It offers acoustic absorption, thermal insulation and non-combustible fire performance in one product.
The slabs are easy to cut, friction fit between framing members and install into wall, ceiling and floor cavities. The 1200mm x 600mm slab format makes them practical for common timber and metal frame applications.
Choose the thickness based on the depth of your cavity. As a general rule, the mineral wool should fill the cavity neatly without being heavily compressed. Over-compressing the slab can reduce its effectiveness and make installation harder.
For acoustic systems, Rocksilk RS45 should normally be used with additional mass, decoupling and airtight sealing. Mineral wool alone will not fully soundproof a wall, ceiling or floor.
If you are unsure which thickness you need, please contact our team before ordering. We can help advise on the correct acoustic build-up for your wall, ceiling or floor system.
Knauf Rocksilk RS45 Acoustic Mineral Wool is a rock mineral wool slab used in acoustic, thermal and fire protection applications. It is suitable for use in walls, floors, ceilings, internal partitions and separating floor systems.
| Product Name | Knauf Rocksilk RS45 Acoustic Mineral Wool |
| Brand | Knauf Insulation |
| Product Type | Rock mineral wool insulation slab |
| Application | Acoustic, thermal and fire protection insulation |
| Material | Rock mineral wool |
| Density | 45kg/m³ |
| Thermal Conductivity | 0.035 W/mK |
| Reaction to Fire | Euroclass A1 non-combustible |
| Binder Technology | ECOSE® Technology |
| Slab Size | 1200mm x 600mm |
| Area Per Slab | 0.72m² |
| Available Thicknesses | 50mm, 75mm and 100mm |
| Facing | Unfaced slab, unless otherwise stated |
| Main Acoustic Function | Sound absorption within wall, ceiling and floor cavities |
| Standalone Soundproofing Product? | No — should be used as part of a complete acoustic system |
| Thickness | Slab Size | Slabs Per Pack | Pack Coverage | Declared R-Value |
|---|---|---|---|---|
| 50mm | 1200mm x 600mm | 10 slabs | 7.20m² | 1.40 m²K/W |
| 75mm | 1200mm x 600mm | 6 slabs | 4.32m² | 2.10 m²K/W |
| 100mm | 1200mm x 600mm | 5 slabs | 3.60m² | 2.85 m²K/W |
Knauf Rocksilk RS45 can be used in a range of applications, including:
Rocksilk RS45 is used to absorb sound inside cavities. It is normally installed between studs, joists or frame members before the plasterboard or acoustic board layers are fitted.
It helps reduce cavity resonance and supports the performance of the complete soundproofing system. It should be combined with appropriate mass, decoupling and airtight sealing for best acoustic results.
Knauf Rocksilk RS45 is an acoustic insulation slab, not a complete soundproofing system on its own.
The final acoustic result will depend on the full wall, floor or ceiling construction, including the existing structure, cavity depth, board mass, decoupling method, perimeter sealing, workmanship and flanking noise paths.
For Building Regulations, fire-rated or compliance-led projects, use the correct tested system specification and seek project-specific advice where required.
Store packs clean, dry and protected before installation. Do not leave mineral wool exposed to weather or standing water.
Wear suitable PPE when cutting and installing mineral wool, including gloves, long sleeves, eye protection and a dust mask. Cut slabs with a sharp insulation knife or suitable saw.
Knauf Rocksilk RS45 Acoustic Mineral Wool is installed within wall, floor and ceiling cavities to provide acoustic absorption, thermal insulation and fire protection support.
For acoustic projects, it should be installed neatly between studs, joists or framing members without gaps, heavy compression or rigid bridging.
Choose the correct thickness for your cavity depth. The slab should fit neatly into the cavity without being heavily compressed.
Check the installation area before fitting. The cavity should be clean, dry and free from loose debris, sharp fixings and obvious gaps.
For soundproofing systems, plan the complete build-up before installing the mineral wool. This may include acoustic plasterboard, resilient bars, Genie Clips, MuteClips, acoustic membranes and acoustic sealant.
Measure the distance between the studs, joists or frame members.
Take measurements at several points because older buildings and timber frames are not always perfectly even.
For a neat friction fit, the slab can usually be cut slightly wider than the cavity, but it should not be forced in so tightly that it becomes heavily compressed.
Place the Rocksilk RS45 slab on a stable cutting surface.
Use a sharp insulation knife or suitable saw to cut the slab to the required size. Cut cleanly and avoid tearing the edges.
Where possible, cut pieces so they fit tightly around studs, joists, noggins and services without leaving open gaps.
Push the slab gently into the cavity so it sits flush with the framing.
The insulation should fill the cavity evenly. Avoid leaving air gaps, voids or loose edges.
Do not heavily compress the mineral wool. Compression can reduce its ability to absorb sound within the cavity and may make the surface uneven for the board layers.
Cut neatly around pipes, cables, sockets, noggins and other obstructions.
Do not leave large holes around services. Small gaps can reduce the overall acoustic performance of the system.
Where services pass through the wall, ceiling or floor, use suitable acoustic sealant or approved fire/acoustic detailing as required by the project.
For wall installations, fit the Rocksilk RS45 between timber or metal studs before installing the plasterboard or acoustic board layers.
Make sure the slabs are supported by the studs and sit flat within the cavity.
For acoustic walls, the mineral wool should normally be combined with suitable board mass and airtight perimeter sealing.
For ceiling soundproofing systems, fit the Rocksilk RS45 between the ceiling joists.
If the ceiling is open from below, friction fit the slabs between the joists or use suitable retention netting where required.
Make sure the mineral wool does not drop, sag or leave open gaps before the ceiling board layers are installed.
For timber floor voids, fit the Rocksilk RS45 between the floor joists to reduce cavity resonance.
Where needed, support the insulation with netting, wire or suitable support battens so it remains in position.
Do not use RS45 as a load-bearing floating floor resilient layer unless it has been specifically specified for that purpose. It is normally used within the cavity rather than as a compressed layer beneath a floating deck.
If the mineral wool is being used in a decoupled system, make sure it does not create rigid bridges between isolated layers.
The insulation should sit within the cavity and should not be packed so tightly that it forces isolated boards, clips, channels or frames out of position.
Once the Rocksilk RS45 is fitted, install the specified plasterboard, acoustic plasterboard or soundproofing board layers.
Follow the board manufacturer’s fixing guidance. In clip and channel systems, only fix boards into the channel and avoid fixing through into the structure behind.
For high-performance acoustic systems, stagger board joints between layers and use acoustic sealant around perimeters.
After the board layers are installed, seal perimeter gaps, service penetrations and small openings with suitable acoustic sealant.
Pay attention to:
Good airtightness is essential because sound can pass through small gaps.
Knauf Rocksilk RS45 Acoustic Mineral Wool helps absorb sound within cavities, but it does not block sound by itself.
The final performance depends on the complete wall, floor or ceiling build-up, including existing structure, board mass, decoupling method, acoustic sealing, workmanship and flanking paths.
If you are unsure which thickness or system is right for your project, please contact our team before installation. We can help advise on the most suitable acoustic build-up for your wall, ceiling or floor.
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