Thermo-loc FRStop Cavity Stop Sock

Fire-rated thermal and acoustic cavity stop sock designed to restrict the spread of smoke and flames within external masonry.
4-hour fire integrity and Class O surface spread of flame classification.
FRSTOP will also further minimise the effect of flanking noise pollution at wall junctions.


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

Product Information

FRstop cavity stop sock

Product CodeCavity WidthDimensionsIntegrity
ACSS5050mm65 x 65 x 1200mm4 hours
ACSS7575mm90 x 75 x 1200mm4 hours
ACSS8585mm100 x 100 x 1200mm4 hours
ACSS9090mm105 x 120 x 1200mm4 hours
ACSS100100mm120 x 100 x 1200mm4 hours
ACSS115115mm130 x 100 x 1200mm4 hours
ACSS125125mm140 x 100 x 1200mm4 hours
ACSS150150mm150 x 100 x 1200mm4 hours

  • 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 requests
  • Meets the requirements of the Robust Detail, Part B and NHBC Standards
  • 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
  • Manufactured using rockwool mineral wool. Rockfibre uses no CFCs, HCFCs in the manufacturing process. Thermal conductivity of Rockfibre insulation 0.037w/mK.
  • 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 and proprietary wall weep vents at 900mm centres to prevent water ingress from bridging the cavity.
  • 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.

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

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