Because yes, paint is more likely to show up dirt and chips, but surely that’s just shabby chic?
What’s more, paint can cover up problems as much as it shows them up. Period floorboards often have modern boards mixed in where repairs have been done over the years, or you may need to patch in new boards yourself to replace damaged ones. Painting the boards makes it easier to disguise the new ones than with wood stain or varnish (although there may be a noticeable difference in the wood grain).
As long as the boards are in good condition, you should be able to use a wood scraper, sandpaper and a handheld sander to clean them off and make them smooth - remember to bang down any protruding nails with a nail punch and hammer, and remove staples and other remnants of the previous floor covering.
Sometimes the boards are in such a bad state that only sanding them with an industrial floor sander will do. Hiring a sander - and an edger for where the sander can’t reach - isn’t particularly expensive, but it’s hot, hard and dusty work.
Once you’ve finished sanding, it’s important to clean the sanded boards thoroughly to get a good final finish. Vacuuming them only goes so far and you’ll also need to wipe them over, ideally with methylated spirits. Removing dust and debris between coats of paint may also be necessary, and to really clean out the gaps between the boards, run a knitting needle, butter knife or screwdriver down them.
Newer boards may contain resinous knots, which will need to be sealed with knotting solution to prevent the resin bleeding through and spoiling the paint. Alternatively, you can use Ronseal Knot Block Wood Primer & Undercoat (from £7.98 for 250ml, B&Q), which seals the knots, primes and undercoats in one, saving you time and effort. Even if you don’t use this product, you will need to apply wood primer/undercoat to the floorboards - try diluting the first coat with about 10% of white spirit so it penetrates the wood better.
After priming and undercoating the boards, you may find that yellow marks appear. If normal paint won’t cover them, use a stain-block paint - Polycell One Coat Stain Stop aerosol (£6.96, Tesco Direct) is a good one because it dries quicker than most stain blocks.
If you need to use the room again soon after your work, a quick-drying floor paint is your best bet - water-based ones dry fastest . However, if you can close the door and wait a while for it to dry, a solvent-based paint will be more durable long term and should require fewer coats than a water-based paint. Again though, back to the pros of a water-based paint, and it shouldn’t yellow over time like a solvent-based one. Basically, you’ll have to work out what benefits are most important to you.
You can also use ordinary wood paint to cover your floorboards then protect it with clear (non-yellowing) varnish, but while this is a cheaper option than a specialist paint, I wouldn’t recommend it. Bear in mind that normal paint is not designed to be walked on, and will wear over time - it pays to pay out more now.