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ClassicBond EPDM Water Cut-Off Mastic
ClassicBond EPDM Water Cut-Off Mastic
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Compression Sealant for EPDM Termination Bars & Fixings
ClassicBond Water Cut-Off Mastic is a one-component, extremely tacky butyl-blend sealant designed to create a watertight compression seal in EPDM rubber roofing systems.
It is applied beneath the membrane before mechanical termination, where it seals around fixings under compression - preventing water tracking into screw penetrations or behind termination bars.
When compressed, the mastic “oozes” into gaps, forming a durable seal that remains flexible long-term.
What Water Cut-Off Mastic Is Used For ▸
Water Cut-Off Mastic is primarily used:
- Beneath termination bars
- Beneath balustrade fixings on balconies
- At compression-type wall terminations
- Anywhere the membrane is mechanically fixed and compressed
It is not a surface sealant - it is a compression-type sealing agent.
Why It’s Critical for Termination Bars ▸
When a termination bar is fixed through the membrane:
- Screws penetrate the EPDM
- Water can track along the fixings
- Movement over time can create small voids
Water Cut-Off Mastic is applied as an 11mm bead beneath the membrane, and when the termination bar is tightened down, it compresses and seals around every fixing point.
Recommended System Practice ▸
It is strongly recommended to use Water Cut-Off Mastic beneath compression terminations, and then apply Lap Sealant along the exposed top edge of the termination bar.
This two-stage approach provides:
- Internal compression sealing
- External weather protection
Application (Overview) ▸
- Ensure all surfaces are clean and dry
- Apply an 11mm bead between substrate and membrane
- Install termination material
- Tighten fixings to create constant compression
Coverage:
- Approx. 3 linear metres per tube at recommended bead size
⚠️ Not suitable for use on insulation
Product Details ▸
- Product: ClassicBond Water Cut-Off Mastic
- Type: Butyl-blend compression sealant
- Colour: Grey
- Service Temperature: -40°C to 93°C
- Coverage: Approx. 3 linear metres per tube
- Shelf Life: 1 year (unopened)
A Roofer’s Perspective ▸
Water Cut-Off Mastic is what actually seals the fixing penetrations beneath a termination bar. Lap sealant protects the edge - but water cut-off seals underneath.
Used correctly, it prevents water tracking through screw holes and protects the roof build-up long-term.
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