How To Sand Wood Floors Like a Professional – Without Leaving Machine Marks!

Screening and Final Preparation for Staining or Finishing

Once you are sure that you have removed all the edger marks, vacuum the floor again to get rid of any stray-grits. Then you should buff the whole floor with a floor maintenance machine with a 100-grit screen on it. You can see now, I have not sanded the floor too finely, but it will feel very smooth to touch, and will be really free of any coarse sanding lines. When you sand a floor past 120-grit sandpaper and then stain it, the stain may not be able to penetrate the slick surface of the wood. Pigment stains (the easiest to use) need the pores of the wood to lodge in, otherwise the stain color will not take. When you wipe these stains on a floor that is too smooth, most of the color will come out too. The final buffing of the floor should be done just before you are ready to stain, or else the grain might rise if the weather is humid at all. The buffer should be worked slowly back and forth against the grain of the floor and then using the same screen (by now quite dull) with the grain of the wood. Some floor mechanics take the extra step and hand buff the areas that the machine couldn’t reach. But in all cases be sure to get as close to the edge as you can to help blend in the edges where the two different machine marks can show up through the stain.

Now, if you are simply going to clear finish (no stain) the floor, you could have skipped some of these steps. Always start out with 36, then 60, but then all you need to do is burnish the 60-grit paper when it is spinning on the machine. Again use a piece of fine sandpaper for this burnishing, and you will have easily (and cheaply) created a fine paper for polishing the floor. In fact you will find the floor so smooth that the no final buffing of the wood will be needed. Any sanding marks will be so fine that a clear finish (any lacquer, OMP, but not water based) will flow out smoothly. Just read my article on how to apply OMP (oil modified polyurethane), still by far the best looking finish out there.

If you are sanding a floor with the intention of applying water based finish, you will have to use the more lengthy method I described in sanding for a stain. Sanding lines are just too visible with this rather bluish pale finish. Water based finishes are a coalescing type of finish. The solids of the finish are contained in little droplets, surrounded by glycol ether solvents. These are held in suspension in the water. They thicken quickly on the bottom of the finish layer after they are applied and will not fill up the fine scratch lines in a poorly sanded floor. In fact the finish bridges over small scratches creating light colored air pockets showing up quite alarmingly in strong light. Most pros charge quite a bit extra knowing that they will have to sand a lot finer for water based finishes. If they don’t know that, they leave you with a poorly finished wood surface, for these less than forgiving water borne finishes.

And that fact that the water in the finish raises the grain on the first few coats, means starting out with a very smooth floor is essential. Some flooring contractors pop the grain of the wood with a wash of distilled water. Let this dry overnight, and vibrate the edges and screen the whole floor the next day. But in this case use a dull screen so you only sand off the “popped grain” wood. This will prevent really severe grain rising caused by water based finishes. You can see why we have to charge a lot more for these finishes.

Oh, and I should also mention that if you are doing a clear finish you should still attack those edges with the vibrator, but don’t bother with the trouble light. The few remaining edger marks won’t be terribly visible with a clear finish. Just be sure that when you fine edged all the coarse edger marks are gone. The vibrator cannot touch these.

The exception to what I have just said is for parquet or herringbone floors. Even without a stain these floor need a buffing. You will need to remove the final cross grain scratches created by the drum sander. These marks will be at the minimum if you follow this advice : When you sand a parquet floor you need to change the sanding direction each time you change to a finer-grit sandpaper. And be sure to check to make sure all the marks from the previous paper are gone. But on the final two sandings, use the same direction across the slats. The final direction should be either along a long wall or pointed toward a large window or a focal point (like a fireplace). This last sanding is best done with burnished sandpaper, which makes very faint cross grain marks. After all the edging is done, switch to the buffer, to remove all the cross grain scratches in at least half the parquet pieces.

Some parquet installers use a special flat aluminum-sanding disk on their buffer that removes these sanding lines a little quicker, but this is a rather specialized and expensive tool. You can do a quite adequate job with a 100-grit screen, just change it often so that it does it’s job. I should say however, the flat sanding disk will do a better job. It would be worth investing in this tool if you do lots of stained parquet. Oh and here is a great place for the vacuum attached buffers. You wouldn’t believe how much dust a buffer can make when you are trying to remove fine cross grain scratches on the parquet.

Whether the floor is parquet or strip now is the time to take a look at the floor surface in the afternoon light to see if there are any chatter marks in the floor. You won’t see these marks with an overhead light, and rarely in the morning or midday. It’s the 3 – 6 PM afternoon angled light that really shows up these errant sanding marks. If they are really obvious, you either haven’t tuned your machine properly or there is a sympathetic vibration between the machine and the floor. This sympathetic vibration problem has only happened to me once in 25 years. An out of balance machine is more often the cause. You could either try buffing the floor one more time, or you could sponge (as I described before) the whole floor with distilled water, allow it to dry over night and begin the buffing all over again. And this time you will have to vibrate the edges first. But do this all gently, just taking off the rough wood. It would be a good idea if you have a really chattered floor to use a flat metal sanding disk on your buffer. This will prevent a dishing out of the grain if you find that you find the chatter marks are taking a long time to buff out. Keep the buffer handle low in this case to prevent the long swirls marks of too aggressive buffer marks.

One warning here about buffing the floor too much with a screen. If your final drum sanding has revealed severe chatter marks and you spend hours with the buffer and sharp screens to take the chatters out, you may over screen the floor and cause a dished out grain effect. I just saw this on a finished floor last weekend, and it was so bad that the flooring contractor, who made the mistake, was terminated from the contract, and lost about $4,000. And new floor mechanic had to be hired to do the job all over. The original floor guy could have avoided this by using the flat aluminum disk with minimal padding on the buffer. And instead of a screen he could have used a double-sided sandpaper disk. These double-sided disks will stay flat even if used with just the rubber pad that is on your wooden buffer disk. Try it without the maroon pad as a cushion.

Let me just review one more time the drum sand-grits I always use on new or old floors in prep for a stain. They are 36 (or 40 if you prefer), 60, 80, then burnished 80. Then the edges are done, and finally a 100-grit screening with a floor buffer. For a clear finish 36, 60, and then burnished 60 (or 100-grit). And then do the edges like I have already described.

Now this concludes the article on preparing a floor for a stain or a clear finish. And if you really think you know all about how to stain a floor you need NOT get my companion article on what stains to buy and how to use them. But did you know there are at least 4 different kinds of commonly used stains and each type has their best application method and preferred wood species? After you have stained the floor be sure and purchase my article on how to apply the oil modified polyurethane finish, without those annoying bubbles and pits. I also address drying and adhesion problems normally associated with this good finish. I’m sorry I had to separate all the articles like that, but doing it one big article would have been too long a read. I want you to be able to digest these vital steps, and the important details, a piece at a time. No other article or book will do this for you. As you can see, I omit no details, or any of my trade secrets that I have learned over 25 years. So this article is quite a bargain after all, I hope you save it and use it.