You sand a wooden floor in three to four passes with progressively finer abrasive: you start coarse (24 to 40 grit) to take the old coating off, then 60 to 80, and you finish on 100 to 120. After that you pick a finish: varnish for maximum durability and minimum maintenance, or hard wax oil for a more natural feel and damage you can touch up in place. Doing it yourself costs roughly 12 to 25 euros per m² in hire and materials, having it done roughly 30 to 55 euros per m².
But do not start there. Start with the question of whether your floor can still be sanded at all. That is the question almost every article on this subject skips, and it is the question people lose hundreds of euros on. An engineered board with a 2.5 mm wear layer that has already been sanded twice will delaminate on the third go. Then you are standing there with a ruined floor and a sander on hire.
Below: how to do that check, when you need to stop (including the asbestos story you really should read), the complete grit sequence, how varnish and oil weigh up against each other, and what it costs.
Step 0: can your floor still be sanded?
Every full sanding takes off roughly 1 to 2 mm of timber, depending on how deep the damage sits and how coarse you have to start. So the thickness of your wear layer decides how often you can do it.
| Floor type | Wear layer | Number of full sandings |
|---|---|---|
| Solid oak boards (18-21 mm) | down to the tongue, roughly 6-8 mm | 4 to 6 times |
| Thick-lamella or engineered board, thick wear layer | 4-6 mm | 2 to 3 times |
| Engineered board, standard | 2.5-3 mm | 1 to 2 times |
| Multi-layer board, thin wear layer | 0.6-2 mm | usually not, at most a very light scuff sand |
| Veneer or laminate | 0.2-0.6 mm or no timber at all | never |
How do you measure your wear layer? Three ways, from easy to thorough:
- At a threshold, a stairwell opening or a ventilation grille you can often see the end of a board. Use vernier callipers or a rule to measure the timber above the glue line or the backing layer.
- Lift one board in a corner or under a radiator, somewhere you can put it back afterwards.
- Look at the tongue. On solid boards the tongue sits halfway up the thickness. Everything above the top of the tongue can be sanded away. Reach the tongue and your floor will split and work loose.
Do you see black lines or dark gaps where glue is coming through, or does the floor feel hollow in places? Then a lot has already gone. Not sure? Get a floor fitter round for an inspection. That costs an hour and it is cheaper than a new floor.
The three situations where you have to stop
1. Black adhesive residue under the floor. This is the most important safety warning in this whole article. Black bitumen or asphalt adhesive, used to stick down parquet, tiles and lino, often contains chrysotile (white asbestos). Sanding, routing or chipping it releases those fibres. Source: Asbestdeskundigen
The exact rules depend on where you live, but the core is the same everywhere: asbestos-containing material must not be worked with abrasive tools. In the UK, work with asbestos falls under the Control of Asbestos Regulations, and sanding an asbestos-containing material is not something a homeowner is allowed to do. Glued-down flooring and adhesive residue are therefore not a DIY job.
In practice: lift a board and see a black, tarry layer under the floor? Stop. Have a sample tested by an accredited laboratory. That costs a couple of hundred euros and it is worth it.
2. The floor is loose or creaks everywhere. Sanding makes creaking worse, not better. A loose floor has to be fixed down first, otherwise the machine bounces on your boards and you end up with waves. Screw or pin the loose parts down first, and only sand afterwards.
3. There is underfloor heating below and you do not know how deep. The sanding itself is not the problem, the finish is: not every varnish or oil is suitable for underfloor heating, and during curing the heating has to be off or turned right down. Read the technical data sheet for the product and switch the underfloor heating off at least 48 hours before you start sanding.
What it costs: DIY versus hiring someone
| Item | DIY | Hiring someone |
|---|---|---|
| Floor sander hire (drum machine) | 40-80 euros per day | included |
| Edging sander hire | 25-45 euros per day | included |
| Abrasive paper and sanding belts | 40-100 euros (depending on area) | included |
| Finish (varnish or hard wax oil) | 5-12 euros per m² | included |
| Dust control, filler, sealant, tape | 30-70 euros | included |
| Total per m² (at 40 m²) | about 12-25 euros per m² | about 30-55 euros per m² |
On small areas (under 20 m²) doing it yourself gets relatively expensive, because the machine hire is a fixed cost. At 60 m² or more, DIY clearly pays. For herringbone, old floors with a lot of unevenness, or floors that need a coloured stain: have it done. Those are exactly the situations where a beginner does not see the difference between beautiful and ruined coming until it is too late.
Allow one to two days of sanding and two to three days of finishing and drying for an average living room.
The machines: which ones do you hire?
You need three. Not two, three.
1. The floor sander (drum or belt sander). This is the big machine for the open area. There are two types:
- Drum sander: a rotating drum with a sanding belt. Aggressive, removes a lot of material, but forgiving it is not. Stand still for one second with the drum running and you have a groove in your floor that you will never get out.
- Belt sander (roller sander): similar principle, slightly larger contact area.
Both demand that you keep moving: you set the machine down with the drum raised, start it, lower it while you are already walking, and lift it before you come to a stop.
2. The edging sander. A heavy orbital sander on wheels for the last 10 to 15 cm along the walls. The big machine cannot reach there. Same rule here: keep moving, in small circular motions.
3. The three-disc or orbital buffer sander (a “trio”) for the final pass. A three-head or orbital machine that lays the last grit down evenly and blends the transitions between the field and the edges. Skip it and later, once the varnish is on and the light comes in at an angle, you will see exactly where your machine ran.
For corners and under radiators: a detail sander or multi-tool, and a decent hand scraper (a floor scraper with a reversible blade, for instance). Scraping by hand along the skirting is slower but gives the neatest transition.
Important: hire machines with dust extraction and connect them to an M-class site vacuum. Oak and beech dust is not harmless: it is classified as carcinogenic with long-term exposure. Wear a dust mask of at least FFP2, preferably FFP3, and ear defenders. These machines make serious noise.
Preparation: where half a day goes
This part decides what the end result looks like. Do not do it by halves.
- Everything out. Furniture, curtains, light fittings. Out of the adjoining rooms too if you cannot close a door on them, because the dust goes everywhere.
- Get the conditions right. Work at 18 to 22 degrees and a relative humidity of about 50 to 60 per cent. For varnishing and oiling this is not advice but a requirement: too cold and too damp and your finish will not dry through properly.
- Switch off the underfloor heating, at least 48 hours beforehand, and leave it off until the finish has fully cured.
- Build a dust barrier. Tape doorways shut with sheeting, and make one way through with a zip or overlapping sheeting. Cover sockets and ventilation grilles. Open the windows on one side and use a fan blowing outwards. Dust you keep outside now is dust you will not have to fish out of your wet varnish later.
- Take the skirting off if you want a clean run right up to the wall. Number the backs in pencil so you put each piece back where it came from. If you want to leave the skirting in place, mask the bottom edge with decorator’s tape.
- Punch every nail head and screw below the surface. Go over the whole floor with a nail punch and a hammer, and set every nail head at least 2 mm below the timber. One proud nail head will rip your sanding belt apart, and a belt costs 5 to 15 euros. This is boring work and it is the most underestimated step of the whole job.
- Check for loose boards and screw them down with countersunk floor screws.
- Vacuum the floor thoroughly, including the gaps.
The grit sequence: which grits in which order
Here is the rule of thumb that applies everywhere: never skip more than one grit. Go from 40 straight to 100 and you will not get the scratches from the 40 out. They show up the moment the varnish goes on, and then you get to start again.
| Situation | Pass 1 | Pass 2 | Pass 3 | Pass 4 |
|---|---|---|---|---|
| Old thick varnish, uneven boards | 24 or 36 | 40 or 50 | 80 | 100-120 |
| Normal oiled or varnished floor | 40 | 60 | 80 | 100-120 |
| Floor in good condition, just freshening up | 60 | 80 | 100-120 | – |
| New untreated floor | 60 | 80 | 100-120 | – |
| Maintenance sand for a new coat of oil | 100 or 120 | – | – | – |
For varnish you usually finish on 100 to 120 grit. For oil and hard wax oil you finish on 120, sometimes 150: with oil you want the pores still open enough to take the oil up, but not so rough that the floor drinks it unevenly and goes patchy. Always check what the manufacturer of your particular product specifies. It is on the tin or in the technical data sheet, and that beats any rule of thumb.
Technique with the big machine
- Sand along the length of the boards and follow the grain. Sanding across it leaves scratches you will never remove.
- On herringbone or basket weave, sand the first coarse pass diagonally (45 degrees to the blocks), then the second pass diagonally the other way, and the final passes along the length of the room. That is how you take out the height differences between the blocks.
- Overlap each run by about a third with the previous one.
- Walk steadily and evenly. Around 1 metre every 2 seconds. Too fast leaves stripes, too slow leaves dips.
- Never stand still with the drum running. Lift it before you stop. This is the mistake that most often turns into an expensive repair.
- Vacuum the whole floor between every pass. A single grain left over from the previous pass will score right through your new, finer one.
Edges and corners
Do the edges after every pass with the big machine, with the same grit. Not: all the passes on the open field first and the edges afterwards. Do it that way and you will see a dark or dull band along the walls later.
The edging sander runs orbitally and so leaves circular scratches behind. You work those out on the final pass with a hand sander or the trio, following the grain. For the last 2 cm and the corners you pick up the hand scraper. Always pull with the grain, never across it.
Filling gaps and holes: the sawdust trick
Got open gaps or nail holes? Collect the fine dust from your vacuum bag from the last, finest pass. Mix it with a little water-based floor filler or wood glue into a thick paste, and work that into the gaps and holes. Because you are using dust from your own floor, the colour matches exactly.
Let it dry and sand lightly with your final grit. Do not do it this way on floors that move a lot (wide solid boards on a timber subfloor): there the filler will crack straight back out in winter. Fill only the holes then, not the long gaps.
Larger holes (knot holes, broken-out corners) you fill with a two-part wood filler in a colour that suits your floor. Fill slightly proud, because it shrinks as it cures.
Varnish or oil: the honest comparison
This is where you really do need to think for a minute, because this choice sets your maintenance for the next ten years.
| Floor varnish (PU, water-based) | Hard wax oil | Pure oil | |
|---|---|---|---|
| What it does | forms a closed film on the timber | penetrates the pores and forms a thin wax layer | soaks fully into the timber |
| Look | matt through to high gloss, slightly “plastic” at high gloss | natural, you still feel the timber | the most natural, warm depth of colour |
| Durability | highest | good, less than varnish | lowest |
| Staining | least prone, water beads off | reasonable, mop up spills quickly | most prone, water leaves marks |
| Maintenance | mop with a neutral cleaner, nothing else | a maintenance product roughly once a year, recoat after a few years | top up with oil 1-2 times a year |
| Repairing scratches | not possible in place, whole room again | can be touched up in place | can be touched up in place |
| Number of coats | 3 (1 primer + 2 top coats) | 2 | 2, sometimes 3 |
| Material cost per m² | 6-12 euros | 5-10 euros | 4-9 euros |
| Suits | families, dogs, hallways, stairs | living rooms, bedrooms, anyone who wants natural | bedrooms, lightly used rooms |
Two things you rarely read that make all the difference:
Varnish is an all-or-nothing finish. Once a scratch goes through to the bare timber, you cannot touch it up. Water gets under the film through that scratch and then you get grey patches. The repair is: sand and varnish the entire room again. With hard wax oil you grab a cloth, a bit of oil, and half an hour later it is gone.
Hard wax oil is not maintenance-free, and that gets forgotten in the shop. Reckon on a maintenance product over the heavily used areas about once a year, and after five years or so a light sand and a fresh treatment. It is not a big job (one day, no machines to hire), but you do have to do it.
My advice: busy family, dogs, or a floor in a hallway? Varnish. Care most about the look and want to be able to touch up scratches yourself? Hard wax oil. Pure oil is beautiful but honestly only sensible in a bedroom or a study.
If you go for varnish, use a water-based two-part PU varnish. It is almost as tough as the old solvent-based varnishes, gives off far fewer fumes and does not yellow. Single-part varnishes are cheaper but noticeably less hard-wearing.
Applying varnish: step by step
- Vacuum and wipe dust-free with a slightly damp (not wet) microfibre cloth or a tack cloth. Wait until the floor is completely dry.
- Test on an out-of-the-way patch. Every piece of timber reacts differently. Half a square metre behind where the cupboard is going, and you know how the colour will come out.
- Primer coat. With water-based varnish the primer raises the grain. That is normal.
- Sand between coats with 150 to 180 grit on a pole sander or by hand, as soon as the primer is dry. Vacuum. Do not skip this: without it your floor will feel like sandpaper.
- First top coat. Work with a short-pile varnish roller or an applicator pad, in runs about a metre wide, parallel to the boards. Always keep a wet edge: start the next run in the still-wet previous one. Do not go back over an area that is already starting to set.
- Waiting time between coats as per the data sheet, usually 2 to 6 hours for water-based varnish.
- Second top coat.
- Curing. Careful walking after 24 hours (in socks). Furniture back after 3 to 5 days. Rugs not until 2 to 3 weeks, and do not mop the floor until it has fully cured.
Always work from the furthest corner towards the door. Sounds obvious, but there is always someone who varnishes themselves into a corner.
Applying oil or hard wax oil
- Vacuum and wipe dust-free.
- Test on an out-of-the-way patch, because oil deepens the colour of the timber considerably. Oak goes noticeably warmer and darker. That is usually lovely, but you want to know before the whole room gets it.
- Apply thinly with a flat spreader, a trowel or a roller. The most important rule with oil: thin beats thick. A thick coat will not dry through and stays tacky.
- Let it soak in as per the data sheet, usually 10 to 30 minutes.
- Buff off the excess with a buffing machine and a white pad, or by hand with a clean cloth. Anything that has not soaked in has to come off. What stays behind turns into a sticky film that holds on to dirt.
- Let it dry as per the data sheet, usually 8 to 24 hours.
- Second coat, same method.
- Curing. With oil, full curing takes longer than with varnish: allow 7 to 14 days before you mop or lay rugs.
The fire safety warning you need to take seriously
Cloths and pads with wood oil on them can catch fire on their own. This is not an urban myth: drying oils such as linseed oil oxidise, and that is an exothermic reaction. In a screwed-up cloth that heat cannot escape, the temperature climbs and the cloth ignites by itself. Source: ABN AMRO Verzekeringen
So: never throw oily cloths into a bucket or a bin in a screwed-up ball. Lay them out flat outside on a stone surface until they are completely dry, or submerge them in a bucket of water and keep them there until you take them away. It costs you ten seconds and it causes house fires every single year.
Seven mistakes you want to avoid
- Skipping grits. Going from 40 to 100 looks like time saved and costs you a second full sanding. Never more than one step at a time.
- Standing still with the machine running. One groove in the middle of your living room and you have to go back two grits to get it out.
- Not punching nail heads down. Wrecked sanding belts, and sometimes a deep scratch down the whole length of your floor.
- Leaving the edges until the end. Gives a visible band along the walls.
- Applying oil too thickly. A tacky floor that smells for weeks and attracts dust.
- Not sanding between coats with water-based varnish. Rough as a scouring pad.
- Putting furniture back too soon. The varnish is dry but not yet cured. Furniture legs press into it and that dent never comes out. Put felt pads under everything, at the very least.
Aftercare: how to keep it looking good
- Felt pads under everything. Every chair leg, every table leg, every little cabinet. Check them twice a year, because grit gets embedded in them and then you are sanding as you go.
- A decent doormat. Grit is what wrecks your floor, not water. A mat 120 cm long (two strides) at the front door catches most of it.
- Keep humidity between 45 and 60 per cent. Too dry in winter opens up shrinkage gaps, too damp in summer gives cupping and buckling. A simple ten-euro hygrometer will tell you whether you need to humidify.
- Never wet-mop, not even with varnish. Just damp, and dry it off straight away.
- Use the maintenance product from the same brand as your finish. All-purpose cleaners and soft soap leave a film that your next maintenance coat will not stick to.
Frequently asked questions
Can I sand my floor myself with no experience?
Yes, as long as it is a straight boarded floor or strip parquet in reasonable condition and you are willing to work calmly. Practise your first runs in a corner where a cupboard is going to stand. Herringbone, old floors with a lot of unevenness, stained or coloured floors and stairs are a different story: have those done by a floor fitter.
How many times can a wooden floor be sanded?
That depends on the thickness of the wear layer. Solid boards can take 4 to 6 sandings, engineered board with a 4 to 6 mm wear layer about 2 to 3, and engineered board with a thin 2.5 mm wear layer usually only 1. Every full sanding takes off 1 to 2 mm of timber. Measure your wear layer at a threshold or a stairwell opening before you start.
Which is better: varnish or oil?
Varnish is the most hard-wearing and the least demanding to look after, but you cannot repair scratches in place. Hard wax oil gives a more natural result and you touch up damage yourself with a cloth, but it needs maintenance roughly every year and a fresh treatment after about five. Busy family and heavy traffic: varnish. Looks and being able to touch it up yourself: hard wax oil.
How long does sanding and refinishing a wooden floor take?
For a living room of about 40 m², allow one to two days of sanding and then two to three days of finishing and drying. The floor takes careful foot traffic after about 24 hours, but varnish is not fully cured for 2 to 3 weeks and oil for 1 to 2 weeks. So do not schedule the job for the week you have visitors coming.
What does it cost to have a wooden floor sanded?
Roughly 30 to 55 euros per m² including the finish, depending on the condition of the floor, the pattern (herringbone costs more) and the finish you choose. Doing it yourself costs about 12 to 25 euros per m² in machine hire, abrasives and finishing product. Always get several quotes and have it stated explicitly how many sanding passes and how many coats of finish are included in the price.
Am I allowed to sand it myself if there is black adhesive under my floor?
No, not without testing. Black bitumen or asphalt adhesive often contains asbestos, and sanding releases those fibres. Have a sample tested by an accredited laboratory. If asbestos turns out to be present, removal by a licensed contractor is compulsory. This is not a risk you take to save yourself a day of hire charges.
Can I sand with underfloor heating below?
The sanding itself is not a problem, provided your floor is solidly fixed. Watch two things though: switch the underfloor heating off at least 48 hours before sanding and keep it off until the finish has fully cured, and check that your varnish or oil is suitable for underfloor heating. Bring the temperature back up slowly afterwards, about 2 to 5 degrees a day.
Can I change the colour of my floor?
Yes, with a stain, a lye treatment or a coloured oil. But this is exactly where DIY goes wrong: colour is merciless at showing up sanding mistakes and uneven absorption. Every spot where you lingered a fraction too long with the machine will show. If you really want a colour (white floor, smoked oak, dark oak), that is the moment to call a professional. If you still want to do it yourself, test extensively on loose offcuts from the same floor.
How do I keep the dust under control?
Hire machines with dust extraction and connect them to an M-class site vacuum. Beyond that: tape doorways shut with sheeting, cover ventilation grilles and sockets, open windows on one side with a fan blowing outwards, and vacuum thoroughly after every pass. You will never get it completely dust-free, but with these measures it stays confined to the room you are working in.
There you go, and soon you will have a floor you get years out of. The real work is not in the sanding, that is broadly walking up and down. It is in the preparation, in not skipping grits, and in the patience to let the finish cure.
Planning to tackle more in the house than just the floor? At Fred’s DIY Plans you will find step-by-step instructions for painting, wallpapering, plastering, tiling and floor work, so you do not have to go hunting for the right order of operations every single time. Have a look here.
Best regards from Fred Schouten, builder and DIYer through and through
PS: those oily cloths. Spread them out or into a bucket of water. Not screwed up in the bin. Small effort, and it may well save you your house.