Floors and substrates
Weight of wall tiling against the background limit (BS 5385-1)
- where
- total weight of tiling (kg/m²)
- tile weight (kg/m²)
- adhesive and grout weight (kg/m²)
- share of the background limit used (%)
- maximum weight of tiling for the background (kg/m²)
- spare capacity (kg/m²)
- tile weight above which solid bedding is required (kg/m²)
Explain this equation
Tells you whether a wall can carry the tiles you plan to fix, and whether BS 5385-1 makes you solidly bed them. Use it whenever heavy porcelain or stone is going on plaster or plasterboard.
Wt is the tile weight from the box or data sheet. Wa is the adhesive bed plus grout, often 4–5.5 kg/m² for a 3 mm cement-based bed. Wlim is the most the background can hold: 20 kg/m² for gypsum plaster or skimmed board, 32 kg/m² for unskimmed plasterboard, more for backer boards.
It is a simple load budget: add up what goes on the wall and compare it with what the wall can hold. The 0.7 comes from the rule that tiles weighing more than 70% of the background capacity must be solidly bedded, even small ones.
Sense check: 9 mm porcelain is about 18–20 kg/m². With adhesive it lands near 25 kg/m², fine on bare plasterboard but over the limit on plaster.
Watch out: a thick bed for large-format tiles can double the adhesive weight. The weakest layer, such as an old skim coat, sets the limit.
Adds tile and adhesive weight and compares it with the maximum weight of tiling the wall background can carry.
Enter your values to see the result.
Good to know
Published limits per m² (tile + bedding + grout): gypsum plaster 20 kg; skimmed 12.5 mm plasterboard 20 kg; unskimmed 12.5 mm plasterboard 32 kg; cement:sand render no general limit if sound. Guide figures for backer boards are typically 40–60 kg, but always use the board maker’s figure. A cementitious adhesive at a 3 mm bed weighs about 4.0–5.5 kg/m² wet; thicker beds weigh proportionally more. Where several layers are bonded together, the weakest layer sets the limit.
Common mistake
Using the tile weight alone. The adhesive bed can add a quarter or more to the load, and a thick bed for large-format tiles can push plaster over its 20 kg/m² limit.
Limits
Assumes the background itself is sound, well bonded and correctly fixed. Mechanical fixing rules for large tiles above 3 m, and weight limits set by tanking systems, are separate requirements.
Sources
- BS 5385-1:2018 Wall and floor tiling – Design and installation of ceramic, natural stone and mosaic wall tiling in normal internal conditions – Code of practice
- The Tile Association Tiling Guide: maximum weight of tiling per m² by background (BS 5385-1)
- The Tile Association: Recent changes to BS 5385-1:2018 (70% background capacity rule; adhesive 4.0–5.5 kg/m² at 3 mm bed)
- Topps Tiles knowledge base: Tiling background weight limits
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the tile, adhesive and grout manufacturers’ instructions, BS 5385 and the Tile Association guidance. Coverage rates vary by product and substrate. Check prices and VAT rules with your own records and HMRC.