Preparation
Primer quantity with dilution
- where
- primer concentrate needed (kg)
- area to prime (m²)
- number of coats
- primer consumption per coat (kg/m²)
- water to add (litres)
- parts water per part primer
- packs to buy
- pack size (kg)
Explain this equation
Works out how much primer to buy, and how much water to mix in, for the area and number of coats on the data sheet.
A is the area, n the number of coats and c the primer used per square metre per coat. Mp is the primer concentrate. d is the dilution, the parts of water per part of primer, so Wt is the water to add. Np is the number of packs of size Ps.
Primer use is proportional to the area and the number of coats. Dilution adds water in proportion to the concentrate, so 1:1 doubles the volume of mixed primer without needing more product.
Sense check: 12 m² at 0.15 kg/m² is 1.8 kg of primer; at 1:1 you add 1.8 litres of water to make 3.6 kg of mix.
Watch out: some data sheets quote coverage of the mixed primer rather than the concentrate. Check, and divide by (1 + d) if so.
Primer for the area and number of coats, and the water to add at the dilution the manufacturer states for the use.
Enter your values to see the result.
Good to know
Mapei Primer G quotes 0.08–0.15 kg/m² depending on porosity, diluted 1:1 under levelling compound on cement screeds and used neat on gypsum. BAL specify two coats crossways on anhydrite screeds. Use the top of the range on thirsty backgrounds. Here the consumption is taken as primer concentrate (conservative); check your data sheet.
Common mistake
Applying primer neat where the data sheet says dilute, or skipping it on anhydrite, which can cause the adhesive or compound to debond.
Limits
Coverage varies with porosity. Some data sheets quote coverage of the mixed product rather than the concentrate: if so, divide by (1 + d).
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.