Key points
- ASTM C1325: fibre-mat reinforced cementitious backer units, dimensionally stable, suitable as a substrate for tile and stone on walls and floors in wet and dry areas.
- ASTM C1288: fibre-cement interior substrate sheets for wet and dry interior areas, classified into four grades by flexural strength.
- US tile council guidance: gypsum board — including water-resistant board — may not be used as a direct tile backing in wet areas.
- To prevent water leaking through the wall in showers and tub surrounds, a waterproofing membrane is applied over the board before tiling.
Written for:OwnerContractorSupplier
In dry construction (light steel framing and interior partitions), gypsum board and cement board are often confused. The difference matters a lot in bathrooms, kitchens and outdoors.
1) Board types by standard
| Board | Standard | Description and use |
|---|---|---|
| Cement board (fibre-mat reinforced) | ASTM C1325 | Dimensionally stable units suitable as a substrate for tile and stone on walls and floors in wet and dry areas1. |
| Fibre-cement | ASTM C1288 | Dimensionally stable interior sheets for paint, wallpaper, stone or tile in wet and dry interior areas, in four grades by flexural strength1. |
| Coated glass-mat water-resistant gypsum board | ASTM C1178 | Gypsum board with a glass-mat face and water-resistant coating, designed for walls and ceilings in bath and shower areas as a tile base1. |
| Standard gypsum board | ASTM C1396 | For dry walls, ceilings and partitions; not used as a direct tile backing in wet areas1. |
2) Bathrooms and showers: what does the code say?
- The residential code (section R702.4.2 in the 2010 New York State edition based on the international code) requires cement, fibre-cement or glass-mat gypsum backers complying with ASTM C1288, C1325 or C1178 as the base for wall tile in tub and shower areas2.
- LATICRETE's guide quotes the US tile council: gypsum board — including water-resistant board — may not be used as a backing for direct tile application in wet or intermittently wet areas1.
Is cement board waterproof? The board itself tolerates moisture without damage, but to prevent water leaking through the wall around tubs and showers the guide recommends applying a waterproofing membrane over the board before tiling1. See waterproofing under tiles.
3) Installation in brief
From the general installation guidance in the same guide (the binding reference is the board manufacturer's instructions)1:
- The framing (wood or steel) must be sound, with deflection not exceeding L/360 for interior walls.
- Fix with non-rusting, self-embedding screws: about every 15 cm at edges and 20 cm in the field, or per the manufacturer.
- Treat board joints with alkali-resistant mesh tape embedded in the same mortar used for tiling, or per the manufacturer's system.
- Waterproofing in shower and tub areas.
- Tile with an adhesive suited to the board and tile. See adhesives.
4) Which to choose?
| Location | Common choice |
|---|---|
| Dry room partitions and ceilings | Standard gypsum board |
| Kitchen and bathroom walls outside the shower (painted) | H1 moisture-resistant gypsum board |
| Shower walls and tub surrounds (tiled) | Cement board, fibre-cement or compliant glass-mat gypsum + waterproofing |
| External cladding and balcony soffits | Cement boards rated for exterior use per the manufacturer |
Indicative table; the final decision follows the manufacturer's system and project requirements.
5) Cement board vs. gypsum board
Cement board
- Not damaged by moisture; suitable as a tile backer in wet areas.
- Some types suit external use.
- Heavier, and harder to cut and finish smooth.
Gypsum board
- Lighter, easier, with a smoother surface for painting.
- Fire- and moisture-resistant types available.
- Not used as a direct tile backer in wet areas.
Sources
The number next to a statement points to its source in this list. Sources back the general information; anything marked “practical advice” is editorial experience, not a quoted source. Anything that affects safety, structural design or electrical installations needs a licensed professional, and in Saudi Arabia the binding reference is the Saudi Building Code.
- 1TDS 294 — Tile & Stone Backer Board Selection Guide (cement board ASTM C1325, fiber-cement C1288, gypsum limits) — LATICRETE International — technical data sheet
- 2Residential Code R702.4.2 — Cement, Fiber-Cement and Glass Mat Gypsum Backers (tub and shower areas) — International Code Council — via UpCodes
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This guide is for general information and planning, based on standards and technical guides. Standards are revised periodically; in Saudi Arabia the binding reference is the Saudi Building Code and the instructions of the competent authorities. For design and execution, use a licensed engineer or technician. Found an error? Tell us.