Old wooden floors that are re-coloured if necessary and varnished for protection look good in almost any situation. You don't always have to machine sand the boards, either; thorough cleaning is often all that is needed prior to the application of a decorative finish and a coat of varnish to seal them and make them hard-wearing.

The pros and cons of sanding
Sanding floors and varnishing them has become very popular, because the finished floor will look good with any room scheme, and is as versatile an asset as you could wish for. If some of the floorboards are damaged, they can be replaced by new ones. And, since the whole room is being sanded back, there will be no discernible difference in the surface color. However, one drawback to sanding is that it reduces the thickness of the wood: floorboards that were once 18 to 20mm/3/4  to 7/8 in, providing solid support and a fair insulation against sound, are reduced by 3 to 4mm/'/8 to '/4  in, depending on the uneven nature of the floor. This may be no problem for you, but in houses with a cellar or exposed beams underneath, the noise level will be increased, as will the draught. If the boards are currently bare and in reasonable condition, consider washing them down and adding color instead of sanding them back. Replacement second-hand boards can be found at architectural salvage yards, if needed; and even a new board or two can be matched in.
Try experimenting with oil-based stains on a scrap of (new) board, mixing them together, and then diluting them with solvent. When you have a reasonable match, brush it onto the new floorboard, and sand it down. Oil-based stains penetrate deeper into the wood, so don't try this with water-based stains.

Cleaning and preparing
Plain wooden boards in period properties were scrubbed vigorously with a mix of sand and water, often resulting in a delicate-looking grey sheen. Elbow work is still required, but modern cleaners and abrasives give every assistance and an impressive result. Start as you would any dirty job, using hot water, abrasive cleaning cream and a stiff brush. Work the brush into and with the wood grain, not across it, and clean small areas of board at a time, washing down immediately with clean water. Clean the entire floor, leave it to dry, and repeat the whole process if necessary.
You can now see if any problem areas remain, such as stains, plaster lumps, or splashes of paint. Plaster, softened by the cleaning process, will lift off with a flexible bladed knife. Stains and old paint need brushing with a water washable paint remover. Wait until the paint blisters, and then scrape it off with a flexible blade.
Clean old boards thoroughly by scrubbing them with hot water and household abrasive cleaner, working with the grain.

When the boards have been allowed to dry, brush on the desired finish, again working with the grain and maintaining a wet edge.

Repeat the brushing process if a paint residue is left, but use wire wool for the best finish and for getting into the grain beneath a stain. You may now be left with a fairly rough board surface. If this is so it is because the water used in cleaning down has raised the wood grain, and the board needs sanding slightly by hand. Wrap a fine grade of aluminum oxide abrasive (120 grit) around a sanding block and gently sand with the grain. It is imperative that the boards are completely dry when you start this job. If the floorboards are smooth after the cleaning process, which they will be if they have been varnished some time previously, they can be 'keyed' to accept a new finish. Gently abrade the surface with a fine grade silicon carbide (wet-and-dry paper) used wet, again working along the grain. Bear in mind, however, that sound and draughts can travel up through gaps between the floorboards.

The next stage
Take time out to review your plans. Is the floor in good condition? If it is, all you need to do is decide on a wood finish. If it isn't, and the boards have shrunk slightly, leaving gaps, or boards have been carelessly lifted by trades' people in a hurry, then you have to decide whether or not to proceed. Entire board lengths can be replaced, but finding a timber match for second-hand boards is becoming more and more difficult. Gaps between boards can be filled with chamfered wooden fillets glued, hammered into place and left to dry. In both these cases you would do well to consider sanding down the floor with a hired industrial sander, to achieve a level and color-matched surface.
You may find that the gaps do not bother you. As long as there is no cellar or basement with exposed joists beneath, electric light will not filter up through the gaps, which can ruin the effect of any stripped floor. If you have access to the joists from the cellar, however, it is a simple enough job to nail hardboard to the underside of the floor, between the joists. Cut the hardboard into long strips that fit neatly between the joists. Tack into position with 18mm/3Ain tacks, at 150mm/6in centers. Don't be tempted into using longer tacks, unless you check first to make sure that the points won't break through the surface of the boards of the floor above.

Colors on washed boards
Old scrubbed boards will often have a grey appearance, and you can accentuate this with your color choice, using a grey-green or pale blue color wash. A dessertspoonful of emulsion paint stirred into a liter of water will provide you with a wash that sinks into the grain, but can be wiped off the surface if desired. This wash can be repeated until the color effect is satisfactory. Then, the board can be varnished or left unsealed. If you want to put color back into the bleached wood, try a wash of dark red, highlighting the grain, followed by an oil-based pine varnish. Dilute the varnish with white spirit so that it can be applied more easily, sinking into the wood surface. Finally, seal with a clear floor varnish.

Machine sanding
Hire centers will rent out two types of sander for your floor: a large machine that looks like an old-fashioned lawnmower with a dust bag attached, for the main floor area, and a small belt or disc sander for getting in close to skirtings. They will supply all the necessary abrasives, and, most importantly, face masks and protective glasses. Make sure you understand how both machines work before you take them home.
Your first job is to hammer down all the nail heads, well below the surface of the floorboards, using a nail set or punch. If you don't take on this tiresome task, the nail heads will rip the abrasive sheets on the drum sander. Sanding a floor raises a lot of dust, and although the machine has a collecting bag, a lot gets into the air, so make sure you are wearing a protective mask and goggles when you start up the machine.

•Run the sander diagonally across the floor at 45 degrees to the
boards, using coarse abrasive paper.
•Change to a medium-grade abrasive, and again sand across the floor, but this time at right angles to your first run.
•Then sand up and down, following the board direction.
•Change finally to a fine-grade abrasive, and finish off sanding with the grain.
•The small sander reaches into skirting areas, doorways, and alcoves where the larger drum cannot reach. Here again, start with the coarser abrasive, finish with the fine.
•Clean dust from the boards before sealing and varnishing.

When sanding a floor, begin by making a series of diagonal passes with coarse abrasive across the boards. Then work diagonally in the other direction with a medium grade of abrasive.
A properly sanded and varnished boarded floor makes the most of the beauty of the wood grain.

Sealing and varnishing
Clear varnishes are readily available but they are expensive. Make sure you have the best quality, and that the varnish is recommended for flooring. Cheap polyurethane varnish intended for internal wood work will not put up with everyday wear and tear, and is false economy. It may crack under pressure of furniture castors, and you could be faced with the prospect of a repeat job. After removing all dust and debris, treat the boards with a sealer and apply a varnish. Next work up and down the boards using medium-grade abrasive. Then fit a fine grade of paper to the machine and repeat the process, working in the direction of the grain. Use an edge sander to work up to the skirtings, using progressively finer grades of abrasive.