What is a wedi board?

A wedi board is a light, water-resistant board made of extruded polystyrene foam (XPS), coated on both faces with glass-fibre mesh and a polymer-modified mortar layer. wedi is the brand of the German manufacturer wedi GmbH. In practice “wedi board” is often used as a generic name for any XPS tile backer board with a cement coating, including other brands.

Build-up

• Core: blue XPS foam. It absorbs hardly any water, insulates and is light.
• Reinforcement: glass-fibre mesh on both sides makes the board stiff and impact resistant.
• Surface: a thin mortar coat that tile adhesive bonds to well.

Boards range from a few millimetres thick (for levelling a wall) to several centimetres (stiff enough for free-standing boxing-in).

Uses

• Walls and boxing-in in bathrooms and showers, such as bath panels, concealed cisterns and pipe boxing.
• A flat, tile-ready surface over uneven walls.
• Light partitions, niches, shelves and shower benches.
• Under floor tiles as an uncoupling or insulating layer (follow the manufacturer’s system instructions).

Installation tips

1. Cutting: use a utility knife or hand saw. Score the surface, snap the board, then cut through the back.
2. Fixing: on masonry, use tile adhesive (beads or dabs) plus plugs with washers. On timber or metal studs, use screws with washers at the stud spacing the manufacturer specifies.
3. Seal the joints: the board itself is waterproof, the joints and junctions are not. Use sealing tape and liquid membrane from the same system, also around pipe penetrations and at the floor or shower tray.
4. No joints in corners: avoid board joints in internal corners or along the edge of a shower drain.
5. Do not mix systems: warranties usually only apply when board, adhesive and sealing products are from one system.

Common mistakes

• Assuming XPS boards alone make a shower watertight, without sealing the joints.
• Using boards that are too thin for free-standing boxing-in, so the tiling cracks later.

Related terms

• Tile backer board
• Waterproofing
• Polystyrene
• Walk-in shower
• Plasterboard

Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.