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Some notes on sanding and varnishing old wooden floors

Until very recently, British houses were constructed with solid wood floors. Since the invention of the fitted carpet, most people have regarded the floorboards as nothing more than a platform to hold the carpet up. This is a shame, because appropriately prepared natural wood floors look very nice, and are hard-wearing and easy to clean. That this is true is obvious from the rise in sales of laminated flooring systems in the last few years; but why spend about £1000 per room for laminated flooring (plus the cost of levelling panels, underlay, etc) when you you probably have good-quality wooden floorboards already?


I only have experience of preparing softwood floors. If you are fortunate enough to have an oak floor, you should probably check with an expert before you attack it with a power sander.

What this article is about

Heavy-duty floor sanders are generally supplied with instructions, and you can find information on preparing wood floors in any DIY manual. What these won't tell you, however, are the problems you are likely to encounter in a real house, and how to overcome them. This article is based on my own experiences over the last couple of years; it is not intended to provide step-by-step instructions, but simply to point out the problems you are likely to experience, and how to overcome them.

Why do it?

If you lift a carpet (and all the other junk that goes under a carpet) you are likely to see something like this:


Clearly you aren't going to want to have this on permanent display. This wooden floor is cursed with paint spills, undefinable stains, overall discolouration, and cracks. However, with a bit of effort (OK, a lot of effort) you can turn it into this:


It isn't perfect, but it's a lot better, and I wouldn't be embarrassed to have flooring like this throughout my house. If you plan the work carefully, the total cost of turning the first picture into the second will work out at about £100 per room. This assumes that you hire the equipment over a weekend, and you can do two rooms in that time. It's a lot cheaper than a laminated overlayed floor, and quicker to do.

Why not to do it

Unless you are lucky, a `real' floor will probably never look as `perfect' as a laminated flooring system. Why? First, the floorboards are generally nailed down, often with enormous brads. These will be visible whatever you do. (However, some tongue-and-groove floors are held down with small nails, and these don't look too obstrusive.) Second, over the years the flooboards shrink, and probably no longer butt together perfectly. Again, tongue-and-groove boards aren't subject to this problem to the same extent. The gaps between boards may be a source of unwanted ventilation (draughts, in plain language). Third, if the floorboards have been exposed, but not varnished, then there will probably be a variation in colour across the room. Sunlight tends to darken the wood, so the brighter end of the room will have darker flooring. Fourth, if the floor is rotten, holed, infested with woodworm, badly cracked or very uneven then you will probably never be able to achieve acceptable results.

A softwood floor will probably always have an `antique' look to it, however it is treated. It will probably be knotty, and have a very strong grain. Of course, many people find this look very appealing in itself. However, you have some control over the degree of `antiqueness' of the final result, as I will explain.


For a successful finish, you need to spend at least as much time in preparation as you do on the actual sanding and varnishing. This is difficult, as the preparation takes a long time and does not give an obvious reward.

It's worth bearing in mind that unless your house is very modern (in which case it may well not have wooden floors, anyway) or you are very lucky, you will find some imperfections in the floor that make it difficult to achieve a perfect finish, if not impossible. You need to decide fairly early in the process how perfect a finish you will strive for. The more perfect the finish, the more time you will need to spend in preparation.

First you will need to expose all the floorboards in the area to be treated. This generally means emptying the room of all furniture. Although it is possible to work around a few items of furniture, it makes the job much more awkward. Moreover, sanding a floor generates a phenomenal amount of dust, so you need to make sure that anything you can't move is well protected from this. In general, you want to work in an empty room if it's at all practicable. Naturally you'll need to remove all traces of carpet, underlay, floor levelling boards, linoleum, etc.

Second, make good any gross defects in the floor. By this I mean, for example, replace or repair broken or loose flooboards. If you do have to replace floorboards, remember that the new floorboards will almost certainly have a different colour to the old ones (unless you take them from another part of the house). This is particularly apparent with pine, which goes from a pale, straw yellow colour to a deep golden yellow over the years. If you are putting new boards next to old ones, then you should consider staining the new boards to match the old. You can get `antiqueing' stains for pine. It's probably best not to try to get an exact match for the colour of the old boards, as the colour you end up with will be a combination of the colour of the stain and the colour of the new boards. That is, it won't necessarily be the same as the colour on the tin. I would suggest getting a light stain, and applying enough coats to bring the colours into agreement gradually. It's best not to stain new boards until after sanding, as sanding will change the colour completely. The same logic applies to the use of wood filler for holes and cracks; you can get wood filler in a variety of colours, but sand the floor first to find the proper colour to use.

If some of the floorboards have lifted from their joists, then you'll need to find a way to fasten them back down (you might need to use screws for this, rather than nails). If you don't they will stop the sander getting to adjacent boards.

At this stage any problems with wordworm or rot will come to light. Naturally, active woodworm needs urgent, specialist attention, as does any sign of dry rot. Wood that is riddled with woodworm, even if inactive, looks ghastly and, in my opinion, is best replaced. The same applies to wood blackened by old, persistent wet rot.

Third -- and this is the really dull bit -- you will need to ensure that the floor is totally smooth. Although the instructions supplied with the floor sander will undoubtedly say that you should remove or hammer down all nails and screws in the floorboards, they don't stress just how important this is. Trust me on this; if the sanding belt hits a nail that protrudes above the surface by more than about a millimetre, the belt will be destroyed. As each sanding belt costs about £10, you don't want this to happen very often. In practice this means getting on your hands and knees, and inspecting the floor in minute detail. Protruding nails should be given a good whack with a club hammer; in my experience it isn't necessary to punch them below the surface (but don't blame me if your sander is more flakey than mine).


In my area, it costs about £100 to hire a floor sander and edge sander for a weekend. If your rooms are completely empty, then you ought to be able to do two good-sized rooms in that time. A floor sander is extremely heavy, and if you're picking one up in a car you might need help to get it in and out. Similarly, carrying one up stairs is not a job you want to do too often.

In short, you need to have your floors fully prepared by the time you pick up the machinery, and be able to work methodically. If you have to keep stopping to hammer down floorboards, or replace the sanding belt, you won't end up getting good value for money.

If you haven't heard a floor sander in action, you'll be appalled by the amount of noise it makes. If you've ever driven or walked around the perimeter road at Heathrow Airport when a jet aeroplane goes overhead, you'll have an idea of the sound volume to expect. This has two implications. First, you will need ear protection (I'll admit to being a bit cavalier about ear protection; I don't normally bother for things like drilling and grinding, but five seconds with a floor sander was as much as my ears could stand). Second, you might like to consider arranging the job for when your neighbours are away. Or buying them a present. It's really, really loud.

In ideal circumstances a floor sander can be operated along the length of the floorboards, and two or three passes is all you'll need. In practice, most floors aren't in good enough condition for this, and you will need to sand diagonally or across the boards as well. If you are working in a narrow hall or corridor, you may be limited in the direction you can work. If the floorboards are uneven (that is, adjacent floorboards have slightly different heights) you wont get away with only length-wise sanding, because the higher boards will prevent the belt getting to the lower ones. In this case, you will probably need to work diagonally.

For rapid progress you will probably want to use a coarse sanding belt. However, a coarse belt will almost certainly score the wood, and give it a new grain in whatever direction the sander is run, so you'll need to use a finer belt as well after the coarse one. In my experience, if the boards are level enough that they can be sanded along their lengths, you only need the coarse belt (this is a floor, after all, not a table-top). But if you want a really perfect finish, allow for two or three passes over the whole floor, with belts of decreasing coarseness.

A floor sander won't usually reach right up to the edges of the room; the best it will manage is a gap of a few inches. This is where the edge sander comes in. An edge sander is a very heavy rotary sander, usually with a pair of handles on top. It will sand right up to the edge of the floor. The manufacturer's instructions will probably say that you should run the sander from side to side, following the wall. It may well have little wheels to make this possible. Where this means working along the length of the flooboards this is quite straightforward. Where this is across the flooboards, it might not be so easy. If your floorboards are not perfectly level, you'll find that the sander won't run evenly from side to side, and will snag on the edges of the floorboards. This will make a horrible mess: disk-shaped scars in the boards. In these circumstances, it may be better to move the sander from side to side in small (half-inch) steps, dropping it down onto the floor for a few seconds at each step. In some cases I have had to dispense with the edge sander altogether, and finish off with a hand-held belt sander. This takes ages, but won't scar the floor. I'd suggest practicing with the edge sander on part of the floor that won't be visible, if possible.

In old houses, the floorboards may be warped, in any direction. In my house, the edges of each floorboard are about a millimetre higher than the middles. This means that the sander does not easily reach the middles, and leads to an appearance like this:


The middle of each board is darker, because the sander can't really get there. If you can't live with this appearance, then you'll need to resign yourself to sanding away several millimetres over the whole floor. Small areas of severe warping can be takled using a hand sander when the rest of the floor is done.


Sanding a floor generates a lot of dust (but see update below...). This dust will remain in the air for several days. I'm assuming that you're going to want to varnish the floor after sanding; you probably don't want dust settling in the wet varnish. Ideally you should wait at least a day between sanding and varnishing.


Varnishing a floor is not like varnishing an ornamental table-top: a bit of uneveness is not going to be noticed. Therefore there's no reason to use brushes, or even rollers, for the bulk of the floor. A floor mop will do just as well, and be much quicker. If you're using a roller, you'll need to fit a long handle on it so you can work standing up. This is for two reasons. First, it will avoid wear and tear on your knees and back. Second, you really don't want to get your nose near floor varnish any more than you really have to.

For a floor you need a really tough varnish. I use Rustin's because it dries very quickly, but there are several brands of specialist floor varnish available. All have in common that they are extremely volatile, and disagreeable to use. Rustin's makes my eyes and nose burn, which can't be a good sign. I'm not sure how dangerous it really is, but I'd be inclined to make sure that there are no pregnant women or small children around. On a warm day, Rustin's is dry to the touch in about 15 minutes, and can be recoated in an hour, so you can apply three coats in one morning. The quick drying properties also mean that any dust that is still settling from the air is more likely to land on a dry patch, rather than getting stuck in wet varnish. A good floor varnish should not scratch if you drag heavy furniture on it, but you'll need at least three coats to get that kind of durability.


An edge sander will grind through radiator pipes if you're not careful. Consider covering the pipes with something while sanding around them.

Hire companies will often supply sanding belts and disks on a `sale or return' basis. This means that if you use them, you pay, but if you don't you can give them back. Unless the hire shop is very close to your house, you should take as many belts and disks on sale or return as they will let you have; it is very inconvenient to run out in the middle of the job, particularly if it's Sunday and all the shops are closed.

If your floor was carpeted, then exposing the floorboards means in effect that you are lowering the floor by a half-inch or so. The result is to make all your doors about a half-inch too short. Also, if you've got exposed floorboards next to a carpeted roon, you need some method of finishing off the exposed edge of the carpet. You can buy brass or steel edgeing strips for this. If you don't finish off the carpet edge, people will catch their feet on it, and it will get scruffy.


I don't endorse particular products or services on these pages; nevertheless if you live in the London area it might be worth having a look at

Floor Sander Hire Ltd

This is a specialist floor sanding company, and their equipment seems to be a lot more modern than the run-of-the-mill tool hire offerings. In particular, their machines are claimed to be virtually dust-free, and have clutches to disconnect the motor from the drum. This should mean that you can stop the drum without physically lifting the machine off the floor, which has got to be a good think.


I've just been told about something called a `square orbital' floor sander. I haven't used one myself, but I'm informed that, instead of a drum, it has a number of orbiting disks that rotate in opposite directions. I can see the advantage of such an arrangement -- the sander would be less inclined to drag the operator around the room, and I imagine that it would be less likely to score its own grain pattern into the wood.


I get a lot of e-mails about gaps. In a house of any age, gaps between floorboards are almost inevitable. These not only tend to be unsightly, but they allow cold air to be drawn up from the under-floor spaces.

There are various ways to tackle this problem, depending on the amount of time, money, and determination at your disposal. I've seen some houses where the gaps have caulked using rope soaked in tar, as was once used on ships. Other people cut long, thin slivers of wood, and knock them into the gaps with a mallet. This typically requires some tedious shaping of the wood so that it doesn't split when knocked down. Ordinary wood filler can be used on gaps of a millimetre or so. If you can get to the underside of the boards, you might be able to staple aluminium bubble foil beneath them, which not only reduces draughts but prevents the loss of heat to the underfloor space by conduction.

On this subject, my attention has recently been drawn to a product called


which is a specialist draught excluder for wooden floors. Gapseal is a polypropylene strip which is supplied in rolls. The strip is scored centrally along its length, so it can be pinched into a V-shaped profile, making it easy to push into the gaps. I haven't used this product myself, but it looks interesting enough to be worth considering.


It's fifteen years since I first wrote this article, but my floors are still in good shape. What isn't in good shape in my lung function. I've suffered a serious of pulmonary embolisms that have had a severe impact on my health. I wrote above about keeping your nose away from volatile industrial chemicals; I wish I had taken my own advice more seriously.

Of course, it might just be a coincidence and, over my life, I've been exposed to many chemicals, dust from woodworking, welding fumes, etc. Look after your lungs.

[ Last updated Tue 22 Feb 19:28:25 GMT 2022 ]