External paving
Bedding mortar for porcelain or stone paving (full bed)
- where
- wet bedding mortar volume (m³)
- paving area (m²)
- average bed thickness (mm)
- waste allowance (%)
- bedding mortar mass (kg)
- bedding mortar per mm of thickness (kg/m²)
- bags to buy
- bag size (kg)
Explain this equation
Use this to price and order bedding mortar for a full-bed patio or path in porcelain or natural stone.
A is the paved area and tb the average bed depth, which Marshalls put at 30–40 mm for 20 mm porcelain. cb is the weight of a 1 mm layer per m² of the bedding product; 2.2 kg/m² matches Steintec’s published figures. w covers spillage and dips in the sub-base.
Volume is area times depth; dividing the mm depth by 1000 gives metres, so V is in m³. Mass uses the per-mm figure directly. Bags are rounded up because you cannot buy part of one.
20 m² at 35 mm is 0.7 m³ before waste, about 1.6 tonnes of bedding, or 65 bags of 25 kg. A 40 mm bed costs about 15% more than 35 mm.
Watch out: the bed is usually thicker than planned once levels and falls are set out. The slurry primer on the slab backs is extra.
Works out the volume and weight of bedding mortar for a full-bed patio or path, and how many bags of pre-mixed bedding to order.
Enter your values to see the result.
Good to know
Porcelain and most stone paving should go on a full, wet mortar bed with a slurry primer on the back of each slab; dot-and-dab or five-spot beds leave voids. Marshalls specify a 1:4 cement:sharp sand bed 30–40 mm thick over a 100 mm Type 1 sub-base, with falls of 1:80 along and 1:40 across. Steintec’s bedding figures (55 kg/m² at 25 mm, 88 kg/m² at 40 mm) work out at 2.2 kg/m² per mm. For a site mix, use the wet volume and your own mix yield.
Common mistake
Pricing from the nominal 30 mm bed when the levels mean the bed will average 40 mm.
Limits
Average bed thickness over the whole area; measure levels first. Slurry primer and sub-base are not included.
Sources
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.