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ClassicBond EPDM Internal Corner Patch
ClassicBond EPDM Internal Corner Patch
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Uncured EPDM Patch for Internal Corners on Wall Edges and L-Shaped Roof Details
The ClassicBond Internal Corner Patch is an uncured, formable EPDM flashing patch used to waterproof internal corners, returns, and complex junctions on EPDM rubber roofing systems.
It is designed to stretch and mould cleanly into internal angles where cured EPDM membrane cannot be folded or dressed without cutting, making it the correct detailing solution for internal corners on walls, L-shaped roofs and in box gutters.
What This Internal Corner Patch Actually Is ▸
This internal corner patch is made from uncured EPDM, the same material used in ClassicBond 9″ PS Elastoform uncured flashing tape.
In practical terms:
- It is a pre-cut, 6" section of 9" uncured EPDM flashing tape
- Laminated to a pressure-sensitive adhesive backing
- Supplied in a size suited to standard internal corners
- Designed for quick, reliable corner detailing without buying a full metre of tape
Like all uncured EPDM flashing, it is self-curing once installed, allowing it to adapt to the detail and form a long-lasting waterproof seal.
When to Use an Internal Corner Patch ▸
This uncured EPDM internal corner patch is ideal for:
- Internal corners where two walls meet
- Returns on upstands
- L-shaped EPDM roof layouts
- Internal corners at:
- Walls
- Parapet walls <150mm high
- Roof returns
- Boxed details
- Internal changes in roof direction
It is suitable for upstands up to approximately 150mm high.
Using uncured EPDM here avoids cutting, folding, or overlapping the main membrane, which can otherwise create potential leak paths.
When to Use a Longer Length of 9″ Uncured EPDM Tape Instead ▸
If you are dealing with:
- Higher upstands
- Multiple internal corners
- Longer internal details
- More complex shapes
It is usually more practical to use ClassicBond 9″ uncured EPDM flashing tape, which can be cut to any length required.
👉 The internal corner patch is best seen as a ready-cut convenience option, while uncured tape offers more flexibility for larger or repeated details.
How the Internal Corner Patch Is Installed (Best Practice) ▸
- Ensure the membrane surface is clean and dry
- If weathered, clean with Weathered Membrane Cleaner
- Apply ClassicBond EPDM Primer to the membrane and upstand
- Allow primer to become touch dry
- Round off the corners of the patch using scissors
- Position the patch and press it firmly into the internal corner, stretching it gently to follow the profile
- Roll immediately with a seam roller and penny roller working from the centre outwards
⚠️ ClassicBond Rubber Primer is required and is not included with this patch.
A Roofer’s Perspective ▸
Internal corners are where EPDM detailing can quickly go wrong if the wrong material is used.
Using uncured EPDM, whether as a pre-cut internal patch or from a roll of 9″ tape, allows the material to mold around the weak point in the rubber, forming a long-lasting watertight seal.
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