Advanced options
Grooved boards drink more than the smooth face: use the rough-timber coverage if in doubt. The oil is the quick bit: cleaning is the job. Deck cleaner or a light pressure wash, 48 hours' drying, then thin coats worked in along the grain with a floor pad or brush, second coat while the first is barely touch-dry. Oil when rain is 24+ hours away.
What The Decking Oil Calculator Works Out
- Oil needed: deck area x number of coats divided by the coverage rate. Decking oil covers about 8m2 per litre per coat, so a 15m2 family deck wants under four litres for two coats; the first coat on rough new timber drinks more (about 6m2/L) and thin stains stretch to 10m2/L.
- Tins to buy: the litres rounded up to whole 2.5L tins, the common UK size. Expect a little left over for the touch-ups where chair legs and the barbecue wear through first.
- Job plan: clean, dry for 48 hours, then thin coats worked along the grain with a floor pad, the second while the first is barely touch-dry. Thin-coats-many is the finish that lasts; a single flooded coat sits sticky and peels.
- Custom coverage and board surface (advanced): type the figure from the tin's small print, and add 25% for grooved boards or 40% for weathered, open-grained softwood, which drink far more than the smooth face.
- Tin size and price (advanced): switch between 1L, 2.5L and 5L tins and enter a price to see the cost per application, per square metre and per litre. 2.5L of decking oil is typically GBP 18 to GBP 35, 5L GBP 30 to GBP 60; the big tin is usually cheaper per litre if you will use it within a couple of seasons.
- Annual upkeep (advanced): cost per application divided by the years between re-coats, with a 10-year total. Oil wears away gracefully and never needs sanding, which is why the annual or biennial top-up beats film-forming paints that fail by flaking.
- Deck cleaner (advanced): litres and bottles of cleaner at about 12m2/L ready-to-use or 40m2/L for a diluted concentrate. Cleaning is the job and the oil is the quick bit.
- Working time (advanced): roughly 6 minutes per m2 to clean and rinse plus 4 minutes per m2 per coat, excluding drying. Oil in the dry mild window (spring or September), rain a day away and dew off the boards, never onto green freshly treated timber.
- Coat comparison table (advanced): litres, tins, leftover and cost for one, two and three coats. Hardwoods and thermally modified boards take their own oils; composite decking takes none, and oil-soaked rags self-combust as they cure, so dry them flat outdoors or drown them before the bin.