Tongue and groove is a profile joint in which one board has a protruding ridge (tongue) that fits into a groove in the adjacent board. This allows the boards to connect seamlessly without gaps. It is the standard joint for floorboards, wall and ceiling panelling, and roof boarding.
How does it work?
Each board has a tongue (protruding lip) on one long edge and a groove (slot) on the other. When fitting, you slide the tongue of one board into the groove of the next.
The result:
- No visible seams
- Boards cannot tilt
- Blind fixing possible (screws through the tongue, covered by the next board)
- Boards can expand and contract without gaps
Where is tongue and groove used?
| Application | Example |
|---|---|
| Floorboards | Solid timber floor, pine or oak |
| Panelling | Wall and ceiling panelling |
| Roof boarding | Timber boards on the inside of the roof |
| Cladding | Some weatherboard profiles with tongue and groove joint |
| Sauna/bathroom | Timber wall finish |
Tongue and groove in DIY projects
Laying a floor
1. Start at the wall with the groove side facing the wall
2. Leave 10-15 mm expansion gap along the walls
3. Slide the next board with the tongue into the groove
4. Tap together with a tapping block (never strike the tongue directly)
5. Fix blind by screwing or nailing at an angle through the tongue
Panelling (wall/ceiling)
1. Start at a straight wall or corner
2. First panel with groove facing the wall, screw to the battens
3. Slide in subsequent panels, fix blind through the tongue
4. Cut the last panel to size and secure
Profile variations
- Square tongue — Standard, straight lip
- Rounded tongue — With a rounded profile, creating a visible groove line (V-groove)
- Double-sided tongue — Tongue on both sides, groove in the middle (for thick boards)
Common mistakes
- Too tight a fit — Always leave a fraction of space. Wood swells with moisture. If the boards are too tight, they will buckle.
- Striking the tongue directly — The tongue breaks off. Always use a tapping block or an offcut as a buffer.
- No expansion gap — Leave at least 10 mm free along walls and obstacles.
Related terms
- Dowel
- Weatherboard
- Half-lap joint
- Floorboards
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