Why Solid Wood Needs Time to Settle

Solid wood is a living material, even after it has been milled, sanded and finished. It takes on moisture from the air when humidity rises and releases it when the air dries out. In a centrally heated British home, relative humidity can swing from around 65% in a damp October to below 30% in a frosty February. Each swing makes the boards expand and contract across their width. Acclimatisation is simply the process of letting your flooring reach equilibrium with the room it will live in, so most of that movement happens before the boards are nailed or glued down rather than after.

Skip it, and you invite the classic complaints: visible gaps between boards in winter, cupped edges, a rippled floor where boards have pushed against a wall, or a hairline split appearing along a tongue. None of these are manufacturing faults. They are the wood doing exactly what wood does when it is fitted at the wrong moisture content.

How Long Should Acclimatisation Take?

There is no single number, and anyone who quotes one without checking your site is guessing. As a working guide for solid wood in a UK property:

• Engineered boards: 48 to 72 hours is usually enough, as the cross-ply base limits movement.
• Solid oak, ash or walnut, 18–20mm: allow 5 to 7 days in the room.
• Wide boards over 150mm: give them the full week, ideally longer. Width magnifies movement.
• New builds and freshly plastered rooms: wait until plaster is fully dry, which can mean four to six weeks after the skim, then acclimatise on top of that.

These are minimums, not targets. If the room is cold, damp or the boards have been stored in a garage or van, add days. The wood will not be rushed by turning the heating up; that just dries the surface and leaves the core lagging behind.

Getting the Room Right First

Acclimatisation only works if the room is already close to its normal living conditions. Before you bring the boards in:

• Close all windows and doors. You are matching the floor to the room, not to the weather.
• Run the heating or cooling as you would when the room is in use. Aim for a steady 18–24°C.
• Get humidity into the 40–60% band. A cheap hygrometer is worth more than any advice you will read online.
• Finish wet trades first. Painting, plastering and screeding all dump moisture into the air.
• Remove the old floor and check the subfloor is dry. A concrete slab should read under 75% relative humidity with a properly calibrated meter, or around 2% moisture content on a carbide test.

If the building is unheated and you cannot heat it, do not fit solid wood. Come back in spring.

Storing the Boards While They Adjust

How you stack the timber matters as much as how long you leave it. Lay the packs flat on a dry, level surface, never on bare concrete where damp can wick up. Use offcuts or battens to keep them off the slab. Keep the packs at least 100mm from walls so air can move around them, and do not stack them so high that the bottom boards are crushed.

Open the packaging. Boards wrapped in plastic cannot breathe, and some finishes will sweat. If the boards are banded, cut the bands and restack loosely, but keep them in their original bundles so you can still identify batch and length. Turn the whole stack once, halfway through, so the top and bottom boards see the same air. If you are working across several rooms, split the packs so each room acclimatises its own flooring.

Checking the Wood Is Ready

Do not rely on the calendar alone. Test the boards before you commit. A moisture meter with pins pushed into the end grain of a few boards should read within 2% of the expected equilibrium for your area, roughly 8–10% for most heated UK homes. Take readings from at least ten boards across different packs and write them down.

If you have a sample board you can spare, weigh it, leave it in the room and weigh it again after a few days. When the weight stops changing, the board has settled. Look for other signs too: boards that have stopped cupping, gaps in the stack that have closed, and a surface that feels neither cold and clammy nor bone dry.

Once the readings are stable, fit the floor promptly. Leaving acclimatised boards sitting around while other trades tramp through the room undoes your work. On the day, keep the heating steady, work from a mix of packs, and leave a proper expansion gap of 10–15mm at every wall, around door frames and at any fixed obstruction. Cover that gap with skirting or beading, never fill it with adhesive or grout.

Done properly, acclimatisation costs you a week of patience. Skipped, it can cost you a floor.