Beads, coving and sundries
PVA sealer / bonding agent: dilution and quantity
- where
- PVA concentrate (litres)
- area to treat (m²)
- number of coats
- coverage per litre of PVA concentrate at that dilution (m²)
- water (litres)
- parts water per 1 part PVA (0 = neat)
- mixed solution (litres)
Explain this equation
This works out how much PVA concentrate and water you need to seal or prime an area at a given dilution, such as 1 PVA to 4 water.
C is the manufacturer’s coverage per litre of PVA concentrate at that dilution, which already allows for the added water. A is the area and n the number of coats. d is the parts of water to each part of PVA, so the water is d times the PVA, and the mixed solution is the two added together.
The coverage figure is quoted per litre of concentrate, so the concentrate needed is total area treated divided by that figure. The water then follows from the dilution ratio.
Sense check: Feb General Purpose PVA at 1:4 covers at least 24 m² per litre of concentrate, so a 20 m² wall needs under a litre of PVA mixed into about 3.3 litres of water.
Watch out: coverage varies a lot with porosity. Follow the plaster manufacturer’s preparation advice, and plaster onto PVA while it is still tacky.
Litres of PVA and water for a sealing or bonding coat, from the dilution and the manufacturer’s coverage per litre of concentrate.
Enter your values to see the result.
Good to know
Feb General Purpose PVA (Sika Everbuild): neat 6–12 m² per litre, diluted 1:3 18–36 m², diluted 1:4 24–48 m² (per litre of PVA, depending on porosity). Everbuild 501 PVA: seal with 4 water : 1 PVA; use neat as a bonding coat for plaster; 3 PVA : 1 water brushed on for cement renders. Use the low end of the range on porous backgrounds. British Gypsum recommend their own primers (e.g. Thistle GypPrime, Thistle Bond-it) for Thistle plasters on many backgrounds; follow the plaster maker’s advice.
Common mistake
Plastering onto PVA that has fully dried to a glossy film; most PVA guidance is to apply the plaster while the bonding coat is still tacky.
Limits
Coverage varies widely with background porosity; the defaults are the conservative end of the published range. Not a substitute for the plaster manufacturer’s preparation advice.
Sources
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the manufacturers’ system and product data, BS 8212, BS EN 13914 and Building Regulations. Coverage rates vary by product, background and thickness. Check prices, VAT and CIS rules with your own records and HMRC.