Materials and coverage
PVA or primer dilution by ratio
- where
- PVA or primer concentrate (litres)
- volume of diluted mix (litres)
- parts PVA or primer
- parts water
- water (litres)
Explain this equation
Splits a diluted mix of PVA or primer into the litres of concentrate and water. Use it when the tin gives a ratio such as 4 parts water to 1 part PVA.
V is the total volume of diluted mix you want. pw and pp are the parts of water and concentrate in the ratio. P is the concentrate and W the water.
Each part is the same size, so one part is the total volume divided by the total number of parts (pw + pp). Multiplying by each ingredient's number of parts gives its volume.
Sense check: 5 litres at 4 water : 1 PVA is 1 litre of PVA and 4 of water. A 3 : 1 emulsion-to-water bonding mix for render, 2 litres in total, is 1.5 litres of emulsion and 0.5 of water.
Watch out: check which way round the ratio is written, and follow the plaster manufacturer's preparation guidance, which may call for a specific primer instead of PVA.
Splits a diluted mix into concentrate and water for any ratio on the tin.
Enter your values to see the result.
Good to know
Everbuild 501 PVA, for example, is diluted 4 parts water to 1 part emulsion to seal porous surfaces, used undiluted as a bonding agent for plaster, and 1:1 or 3 parts emulsion to 1 water as a bonding agent for cement renders. Always follow the plaster manufacturer's background preparation guidance: some specify their own primers or bonding agents for gypsum plasters and advise how long to leave before plastering.
Common mistake
Getting the ratio the wrong way round (1 water : 4 PVA instead of 4 water : 1 PVA), or plastering onto PVA that has dried to a glossy film, which can stop the plaster bonding.
Limits
Simple volume split. Coverage per litre depends on the surface porosity and is not given on all data sheets.
Sources
- Sika Everbuild 501 Universal PVA Bond technical data sheet (seal: 4 parts water to 1 part emulsion; render bonding: 1:1 or 3 emulsion : 1 water)
- British Gypsum White Book: Thistle plaster finishes (coat thicknesses, coverage per 25 kg bag, dry set weights, minimum temperature 2 °C until dry, plaster must be thoroughly dry before decorating)
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.