MASONRY CAVITY STOP SOCK 552 is designed to prevent passage of fire through concealed voids within the external fabric of a masonry wall construction.

The polythene enclosed rockfibre barrier is manufactured in bespoke sizes to suit the specified cavity width.

The barrier is held in place under compression between the inner block work and outer masonry leaf.



Masonry Cavity Stop Sock 552 assists in satisfying requirements of guidance documents such as Approved Document B and The Scottish Technical Handbook.

The product reduces flanking sound transmission at separating wall and floor junctions and complies with Robust Detail (Appendix A) as a “cavity stop”.

Suitable for both vertical and horizontal positioning to the edge of cavities, around openings, at separating compartment lines and to sub-divide cavities.


• Designed for installation within masonry cavities
• Accommodates a maximum void of 175mm
• Easy installation process
• Installed under compression
• For voids up to 150mm a minimum compression of 15mm is required, thereafter 20mm compression is required up to the maximum void of 175mm
• Tested and assessed to the basic principles of BS 476-20: 1987
• Suitable for both vertical and horizontal orientation
• Solutions available offering either 60 minutes or 120 minutes fire resistance performance

When installing it may be necessary to consider additional use of DPC’s and/or cavity trays in line with relevant Building Control guidance.

Cavity Stop Sock 552 positioned in a vertical and horizontal orientation around a window opening.

Product Performance

Cavity WidthStop Sock Size required for 60 minutes integrity/15 minutes insulationStop Sock Size required for 120 minutes integrity/60 minutes insulation
50mm65mm x 65mm65mm x 65mm
60mm75mm x 90mm75mm x 150mm
75mm90mm x 120mm90mm x 150mm
85mm100mm x 120mm100mm x 150mm
100mm115mm x 120mm115mm x 150mm

Other sizes are available

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