Minimum requirements before you start
Fibre cement boards must be rigid, securely fixed, dry, and undamaged before any priming or tiling begins.
Rigidity
- Boards must not flex at all. Even slight movement will lead to cracked grout, hollow tiles, or debonding.
Fixing
- Boards must be fixed with corrosion resistant screws at correct spacing and fully supported behind.
Condition
- Boards must be free from moisture damage, mould, swelling, or deterioration.
Quick checks that tell you what prep you need
Identify the board type
If the board flexes even slightly under hand pressure, it is not fit for tiling.
- Exterior grade fibre cement boards are suitable for tiling when properly supported.
- Interior tile backer boards that are specifically designed for tiling and are the preferred option for wet areas.
- Fibre cement ceiling boards may only be tiled if they are designed for tiling, fixed correctly, and fully supported.
Flex test
- Press firmly on different areas of the board. Any movement indicates insufficient support and must be corrected before tiling.
Support check
- Boards must be fixed to timber or steel studs at 300 to 400 mm centres, or to solid masonry backing. Wider spacing causes flexing and tile failure
Fixing check
- Screws must be corrosion resistant, correctly spaced at approximately 200 to 300 mm, flush with the surface, and not protruding. Loose or missing screws must be added.
Joint check
- All joints must be taped with alkaline resistant mesh and filled with fibre cement jointing compound. Open or untreated joints will crack behind tiles.
Preparation steps for suitable boards
Clean the surface
- Even new boards must be cleaned. Remove all dust using a brush or vacuum. Cutting fibre cement produces fine chalky residue that interferes with adhesion and must be removed.
Remove surface residues
- Some boards have a light release coating or surface residue from manufacturing. Light sanding may be required to remove this and improve bonding.
Repair damage
- Repair edge chipping, holes, or cracks using a suitable fibre cement or exterior grade filler. Do not tile over damaged boards.
Priming fibre cement boards
- Fibre cement boards are absorbent but not weak. Priming helps control suction, improve early bond, and reduce the risk of dry out.
- Apply a uniform coat of Kwik-Key diluted 1:1 with water. Apply using a block brush, roller, or spray for larger areas. Allow the primer to dry to a thin, clear film.
- Neat primer is not normally required unless the board is extremely porous or weather damaged.
Waterproofing in wet or exposed areas
In showers, bathrooms, and exterior applications, fibre cement boards must be waterproofed before tiling.
- Apply a suitable waterproofing system such as Kwikproof in accordance with the manufacturer’s instructions. This typically involves two coats with reinforcing membrane at corners, joints, and penetrations.
- Allow the waterproofing to cure fully before tiling.
- Waterproofing prevents moisture migration behind tiles and protects the structure behind the boards.
Coverage rules (bond quality)
- Aim for at least 95 percent adhesive coverage, especially in wet areas.
- Lift tiles regularly during installation to confirm full contact and proper ridge collapse.
Movement and joints
- Although fibre cement is dimensionally stable, the structure behind it may move.
- Movement joints are required at perimeter edges, internal corners, every 3 metres horizontally and vertically, over structural breaks, and where fibre cement meets another substrate. Fill these joints with a flexible sealant. Do not grout movement joints.
Never tile over these fibre cement conditions
- Stop and fix first if boards flex when pressed, stud spacing exceeds 400 mm, boards are not screwed correctly, joints are not taped, boards are severely water damaged, primer has not been applied, waterproofing has not been completed in wet areas, mould or fungus is present, holes or cracks are left unpatched, or screws are rusty or protruding.