RW3 Rockwool 100mm

ROCKWOOL RW3 100mm Technical Specifications

ROCKWOOL RW3 100mm Acoustic Mineral Wool is a semi-rigid stone wool insulation slab used for acoustic, thermal and fire insulation in walls, floors, ceilings, partitions and roof constructions. With a nominal density of 60kg/m³, RW3 is commonly used within acoustic soundproofing systems to absorb sound within cavities and reduce resonance.

Product Specification

Suitable Applications

ROCKWOOL RW3 100mm can be used in a wide range of acoustic, thermal and fire insulation applications. It is commonly installed within:

• Stud walls and partition walls
• Party wall soundproofing systems
• Floor joist cavities
• Ceiling voids and suspended ceiling systems
• Drylining and acoustic wall systems
• Roof and general building insulation applications
• Home offices, studios, media rooms and commercial spaces

Acoustic Use

ROCKWOOL RW3 is used to help absorb sound within a wall, floor or ceiling cavity. Its stone wool fibre structure helps reduce sound movement inside the void and can improve the overall performance of a complete soundproofing system.

RW3 is mainly used to help with airborne noise, such as voices, TV noise, music and general room-to-room sound transfer. In floor and ceiling systems, it can also support the wider acoustic build-up by reducing resonance within the cavity.

Sound Absorption

ROCKWOOL’s RW Slabs datasheet lists RW3 at 100mm thickness with a practical sound absorption coefficient of 1.00. This makes 100mm RW3 a strong option for deeper acoustic cavities where sound absorption is required.

Common System Uses

• Between timber studs in wall soundproofing systems
• Between floor joists as part of a floor soundproofing build-up
• Above suspended ceilings or within ceiling voids
• Behind acoustic plasterboard systems
• Combined with Tecsound acoustic membranes
• Combined with resilient bars or furring channel systems
• Used with acoustic sealant to reduce weak points around edges and junctions

Important Performance Note

ROCKWOOL RW3 is an acoustic insulation slab, not a complete soundproofing system on its own. It performs best when used inside a full wall, floor or ceiling build-up with suitable acoustic boards, membranes, isolation products and properly sealed joints.

The final soundproofing result will depend on the existing structure, cavity depth, installation quality, surrounding materials and how well gaps and flanking paths are controlled.

Handling Advice

ROCKWOOL RW3 slabs can be cut to fit between studs, joists and other framing. For best results, cut the slabs neatly so they fit snugly within the cavity without being heavily compressed. Over-compressing mineral wool can reduce its effectiveness within the acoustic build-up.

If you are unsure whether 100mm RW3 is the correct thickness for your project, please contact our team before ordering. We can help advise on the most suitable insulation and soundproofing system for your room, noise issue and available cavity depth.

How to Install ROCKWOOL RW3 100mm Acoustic Mineral Wool

ROCKWOOL RW3 100mm Acoustic Mineral Wool is used to fill wall, floor and ceiling cavities as part of an acoustic insulation system. It helps absorb sound inside the void, reduce resonance and improve the overall performance of the soundproofing build-up.

RW3 is straightforward to install, making it suitable for both DIY users and trade installers. For the best result, the slabs should be cut neatly and fitted snugly into the cavity without being heavily compressed.

What You’ll Need

• ROCKWOOL RW3 100mm Acoustic Mineral Wool slabs
• Measuring tape
• Insulation saw or sharp serrated knife
• Straight edge or board for cutting
• Gloves
• Long-sleeved clothing
• Dust mask
• Safety glasses
• Waste bag for offcuts
• Acoustic sealant, if sealing around the system

Before You Start

Check the cavity depth before installing the slabs. ROCKWOOL RW3 100mm is best suited to cavities deep enough to accept a 100mm slab without heavy compression.

The slab should fit neatly between studs, joists or framing. Avoid forcing the insulation into spaces that are too shallow, as over-compression can reduce the acoustic benefit and make the installation less effective.

Step 1: Prepare the Area

Before installing RW3, make sure the cavity or frame is ready. The installation area should be:

• Clean — remove loose dust, debris and leftover material.
• Dry — avoid installing insulation into damp cavities.
• Clear — check for cables, pipework, fixings and obstructions.
• Stable — make sure framing, joists or battens are secure before fitting the slabs.

Where cables or services are present, take care not to damage them during cutting or fitting.

Step 2: Measure the Cavity

1. Measure the width and height of the cavity between studs, joists or framing.
2. Check the cavity depth to make sure 100mm RW3 is suitable.
3. Mark the required slab size before cutting.

For a snug fit, cut the slab slightly oversized by a few millimetres. This helps the mineral wool hold itself in position without leaving gaps at the sides.

Step 3: Cut the ROCKWOOL RW3 Slabs

1. Place the slab on a stable cutting surface.
2. Use a straight edge or board as a guide.
3. Cut the slab with an insulation saw or sharp serrated knife.
4. Keep cuts neat so the slab fits closely around the frame and any services.

Cut carefully around pipes, cables and other obstructions. Avoid leaving gaps, as empty spaces can reduce the overall acoustic performance of the cavity.

Step 4: Fit the Slabs into the Cavity

1. Place the cut slab into the cavity.
2. Push it gently into position.
3. Make sure it fits snugly between the studs, joists or framing.
4. Check that the slab fills the full depth and width of the cavity where possible.

The insulation should sit securely without falling out, but it should not be crushed or heavily compressed. A neat, friction-fit installation is usually best.

Step 5: Fill Gaps and Awkward Areas

Use offcuts to fill small gaps around edges, pipes, joists and awkward spaces. The aim is to keep the cavity evenly filled with no obvious empty areas.

For acoustic performance, continuity matters. Sound can travel through weak points, so take time to fill irregular spaces properly.

Step 6: Add the Next Acoustic Layer

Once the RW3 is fitted, the next layer of the soundproofing system can be installed. Depending on the project, this may include:

• Acoustic plasterboard
• Standard plasterboard
• TECSOUND acoustic membrane
• Resilient bars
• Furring channels
• Floating floor layers
• Acoustic sealant around edges and joints

ROCKWOOL RW3 works best as part of a complete acoustic build-up. It absorbs sound within the cavity, while boards, membranes and isolation products help add mass and reduce vibration transfer.

Installing RW3 in Walls

For stud walls and party wall upgrades, fit the RW3 between the vertical studs. Cut the slabs to fit snugly, then install the chosen board or acoustic lining system over the frame.

For better results, combine RW3 with acoustic plasterboard, Tecsound membrane, resilient bars or furring channels, depending on the wall construction and the level of performance required.

Installing RW3 in Floors

For timber floors, fit RW3 between the floor joists. The slabs should sit securely within the void without dropping or leaving gaps.

RW3 can help reduce sound movement through the floor cavity, but impact noise from footsteps normally requires additional materials such as acoustic underlay, resilient layers or a floating floor system.

Installing RW3 in Ceilings

For ceiling systems, fit RW3 between ceiling joists or within the ceiling void. Work carefully overhead and cut the slabs to manageable sizes where needed.

For improved ceiling soundproofing, RW3 is commonly combined with resilient bars, furring channels, acoustic plasterboard, Tecsound membrane and acoustic sealant.

Installation Tips

• Wear PPE — use gloves, long sleeves, eye protection and a dust mask when cutting and fitting mineral wool.
• Cut slightly oversized — this helps the slabs friction-fit into the cavity.
• Avoid over-compression — heavily compressed insulation can reduce acoustic effectiveness.
• Fill the full cavity — avoid gaps around edges, joists, studs, pipes and cables.
• Use offcuts carefully — small pieces can fill awkward spaces and reduce waste.
• Combine with the right system — RW3 is most effective when used with suitable acoustic boards, membranes and sealants.

Important Soundproofing Note

ROCKWOOL RW3 is an acoustic insulation slab, not a complete soundproofing system by itself. It helps absorb sound within the cavity, but the final performance depends on the full wall, floor or ceiling build-up.

For best results, combine RW3 with suitable acoustic boards, membranes, isolation products and acoustic sealant. If you are unsure how to use RW3 100mm in your project, please contact our team before fitting. We can help advise on the most suitable system based on your room, cavity depth and noise issue.