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Get Your Floor Sanding Up To Scratch

Terry Guilford on choosing your grits to use

IN some respects at least, the old days were easier. Sure driving back from a job with a few half used cans of Acid Cat lacquer knocking around in the back of the van were guaranteed to have you driving like an alcoholic after a spectacularly successful night out with George Best.
But to balance that out, (of course balancing anything after using acid catalyst was practically impossible) the sanding part at least was easy.
So assuming that my years of using high VOC (very orrible commodities or actually volatile organic compounds, for those in any doubt) haven’t damaged my brain permanently! What the hell am I talking about?
When I started sanding it could be done by a blind village idiot after the night out with the genial northern Irish sportsman. All it required was some kind of drum sander (only posh companies had belt sanders), an edger and plenty of stamina.
The only time you heard about random orbitals, rotaries, planetaries and extractors was on an episode of Star Trek! What started the change was, in fairness, a drive by some to raise the quality of the sanding and lower the amount of dust, but the real catalyst was the new VOC regulations.
Let me elaborate. As I have said on several occasions water-based and oil or wax oil products are much less forgiving when it comes to scratches prior to application, particularly scratches across the grain.
Although I am not particularly proud to admit it now, my initial attempts at floor sanding involved sanding up to (probably … it isn’t etched on my memory) 100 or 120 grit on both the drum and edge sander and then whacking on the finish. We got away with this because the types of finish we were using didn’t highlight the scratch, but boy did we get a shock when starting to make the switch to the VOC compliant products!
At least at this point in my floor sanding career I had had the good fortune to meet up with an old timer and the day I spent in his company was the most valuable day ever (sorry dear, I mean in floor sanding terms). I now knew, thanks to Noel, that a higher standard of sanding could be achieved, but it just hadn’t been necessary up to this point.
So now we started rigorously applying the techniques that I had learned. First off, don’t skip grits on you big machine, so if you start at 40 grit you must then go through 60 and 80 if you intend to stop at 100 grit. If you can imagine that each piece of grit on a belt will leave a scratch on the wood which in cross section resembles a mountain and a valley (albeit slightly smaller than the real geographical features).
When you use the correct higher grit to go over that scratch you will remove it entirely and replace it with a slightly smaller ‘mountain’. However if you skip a grit you don’t remove the high point of the original scratch, you just create a small ‘valley’ in the top of it. So don’t skip grits on you main machine!
The next point is that it is ok to skip grits with your edger, but it is not ok any longer to finish with your edger. An edger generally has a metal or hard rubber plate to which the sanding disc is attached, this means that it is very unforgiving and aggressive, which is of course what it needs to be to remove old finish, dirt and scratches from the surface of the floor.
Combined with the fact that its motion is entirely rotary (there is no planetary or random element) it means the surface it leaves isn’t good enough for modern finishes. Enter the random orbital sander or ROS for short. I first became aware of these machines during my short career selling tools to the motor trade and I’m guessing that’s where they started out.
The best of these have Velcro backing pads of differing hardness which means you can vary the amount of flex beneath the abrasive depending on the material you are sanding. The real benefit is however in the ‘random’ element of the machines title, you see an Edger just spins whereas a ROS actually spins and has some lateral movement at the same time, which means it isn’t just grinding away at the same spot with every revolution.
This random action gives a much smoother and scratch free finish to the wood and matches the scratch patterns left by the rotary or planetary machines that are going to be used in the ‘field’ area of the floor.
So now moving on to the central area of the floor or the field as it is often referred to. Most people believe that you always have to sand wood in the direction of the grain which is true when using the lower grits but for a really good finish you need to cut across the grain using fine grits to remove all those ‘mountains and valleys’. This can be done with either a rotary machine using screens (a kind of fine mesh with fine grit on the strands of the mesh) or better again multi pads (a special pad from Jost which gives a better finish and doesn’t shed like the screens).
Alternatively a planetary machine, usually with three heads, can be used with fine paper. These machines generally sand at one grit higher than the number on the paper (i.e. an 80 grit disc on a planetary machine will give the equivalent finish to a 100 grit on a non- planetary ) and generally have dust extraction built in to the machine.
Planetarys’ as well as giving you a more random action, also provide for a flatter floor since they don’t ride into ‘valleys’ but try to flatten the ‘mountains’. However this is a double edged sword, especially on old floors that are impossible to flatten out but where the valleys still need smoothing before the finish is applied.
I hope this stroll through the sand (paper) has been useful, I suspect it might be more inclined to drive you the local hostelry, if you bump into a sportsman with too much cash and too little to occupy his time, be careful.
Terry Guilford is technical director of The Ultimate Floor Sanding Co, a corporate member of the National Carpet Cleaners Association (NCCA).

This article has been reproduced from the Contract Flooring Journal website. You can find them at