External paving
Paving jointing compound (resin or cementitious) quantity
- where
- compound per m² of paving (kg/m²)
- slab length and width (mm)
- joint width (mm)
- joint depth (mm)
- density of the filled joint (kg/L)
- coverage per tub (m²)
- tub or bag size (kg)
- total compound needed (kg)
- paving area (m²)
- waste allowance (%)
- tubs to buy
Explain this equation
Use this to order jointing compound for a paved area from the slab size and the joint you are filling.
(L + W) / (L × W) is the length of joint per unit area: each slab owns one long and one short edge. jw × d is the cross-section of the joint. ρj turns that volume into weight; about 2.2 kg per litre fits Steintec’s published coverages.
With L, W, jw and d all in mm, the joint volume comes out directly in litres per m², so multiplying by kg per litre gives kg per m² with no further conversion.
600 × 600 slabs, 4 mm joints, 20 mm deep: about 0.59 kg/m², so a 12 kg tub does about 20 m². Wide 10 mm joints on 24 mm slabs use three times as much.
Watch out: depth is the full depth raked out, usually the slab thickness. Random and mixed-size patterns have more joint per m².
Estimates jointing compound for paving from slab size, joint width and depth.
Enter your values to see the result.
Good to know
Joint length per m² is (L + W) ÷ (L × W); times the joint cross-section gives litres per m², and times the filled density gives kg. Back-calculating Steintec’s published coverages (600 × 600 × 20 at 4 mm, 20 m² per 12 kg; 600 × 1200 × 20 at 4 mm, 27 m²) gives about 2.2 kg per litre of joint. Use your product’s figure if it differs. Rake the bedding out of the joints to full depth so the compound is not starved.
Common mistake
Taking joint depth as 10 mm when the mortar has been raked out to the full 20 mm slab depth; you run out halfway through.
Limits
Straight-grid layout; random patterns have more joint per m². Steintec’s 600 × 900 × 20 at 6 mm row does not fit the same density (it implies about 1.9 kg/L), so treat the default as approximate.
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.