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Thermo-loc FRStop Cavity Stop Sock

Fire-rated thermal and acoustic cavity stop sock.

Use cases:

  • To restrict the spread of smoke and flames within external masonry
  • To further minimise the effect of flanking noise pollution at wall junctions

The Thermo-loc FRStop is also available as a fire-rated cavity stop sock for timber frame construction. Please see the datasheet for further details.

For more information call 01405 765567 Free next day delivery *

View product range & add to quote

Features & Benefits

FRstop cavity stop socks are lengths of low resin, non-combustible, rockfibre mineral wool sleeved in 50 micron polythene for on-site weather protection.

  • 4 hour fire integrity
  • Polythene encapsulated cavity stop sock
  • Available in standard widths of 50, 75, 85, 90, 100, 115, 125 and 150mm
  • Special cavity widths are available on request
  • Meets the requirements of the Robust Detail, Part B and NHBC Standards


Technical Information


  • Satisfies all NHBC requirements
  • Complies with all relevant Building Regulations
  • Meets all relevant British Standards
  • Non-combustible to BS476 : Part 4 1970 (1984) Class 1
  • Surface spread of flame to BS476 part 7 1987
  • Class O to the Building Regulations

Material and colour choice

  • Manufactured using rockwool mineral wool
  • Rockfibre uses no CFC’s, HCFC’s in the manufacturing process
  • Thermal conductivity of Rockfibre insulation 0.037w/mK

Installation advice

  • FRstop is designed to friction fit within the cavity and is easily installed both vertically and horizontally into the cavity during construction. Care should be taken to ensure butt joints are closely fitted and the cavity sock fully fills the cavity.
  • This method should be incorporated with a preformed horizontal cavity tray (refer to Technical Department for appropriate type) and proprietary wall weep vents (Timloc product code 1143) at 900mm centres to prevent water ingress from bridging the cavity.

How to order

  • To calculate quantities divide the overall length of the required cavity wall run by 1.2m, allow an additional unit for each corner for cutting. Always round up to the next whole number
  • Determine and stipulate the cavity width that FRstop needs to suit

Bill of quantity

F30 Accessories/sundry items for brick/block/stone walling


  • Manufacturer: Timloc Building Products, Timloc House, Ozone Park, Howden, East Yorks. DN14 7SD. T: 01405 765 567 W:
  • Types(s) and location(s): FRstop - thermal and acoustic fire stops to be installed vertically and horizontally as work proceeds. Position where a party wall meets the cavity wall or at floor levels, supplied in 1.2m lengths and butt jointed.
  • Reference: ACSS Range
  • Options: ACSS50 – 50mm cavity
  • ACSS75 – 75mm cavity
  • ACSS85 – 85mm cavity
  • ACSS90 – 90mm cavity
  • ACSS100 – 100mm cavity
  • ACSS115 – 115mm cavity
  • ACSS125 – 125mm cavity
  • ACSS150 – 150mm cavity
  • nbs plus
  • riba

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