Of all the steps in hardwood floor installation, sanding is by far the least
favorite, and not because it's boring. I can't imagine doing this for a living,
but some people do it.
I should note that the rental floor sanders are very noisy and hearing
protection should be worn, as well as dust masks.
The beginning of the sanding ordeal, I mean... project.
Note the fan in the window. We found that by blowing the air out we could
expel almost all of the dust that the sanders didn't catch with their dust
We covered the ceiling fan with an old bed sheet to keep the
sanding dust off.
This is The Beast:
The Silver Line drum sander. The first time we installed a floor, in a
second-story bedroom, my back ached for days from carrying this monster up
the stairs. And that was with a helper.
And this is The Battle:
What looks like a gap between two boards is actually a difference in
height of about 1/32" (about 1 mm).
The Hard Work Starts Here:
As with any sanding task, the first sanding is done with the coarsest
sandpaper, in this case 20 grit.
If you've ever used one of these machines,
you can see we are cheating. The dust bags are inflated when in use, not
limp. We just posed with the machine turned off because it was easier to
communicate that way.
The initial step in sanding a new floor with uneven board
heights is to sand at a 45 degree angle to the grain.
In the photo at right you can see some diagonal scratches. This shot
was taken after just a few passes, and the height difference is still
It can take quite a few passes of the sander to remove these small peaks. The
diagonal sanding was by far the longest procedure. The precision of the
tongue-and-groove milling will determine how much of this sanding is required.
There is a pattern that must be followed with drum sanders:
successive passes working from right to left.
The sanding drum is tapered slightly, and it cuts deeper on the left
(where the diameter is larger) and the right side feathers out the deeper
scratches. For this reason the right-to-left pattern must be followed.
The commonly recommended method is to advance 2 to 4 inches each pass.
If you think about it, 2 inches of advancing each pass isn't very much. The
work progresses very slowly. This is just plain old labor, and tedious labor at
To make matters worse, we found that the only way to make serious progress
was to lift up on the handle as the sander was pulled backwards. This takes
weight off the back rollers and puts more weight on the drum (you can hear the
motor working harder). But this puts a lot of strain on the forearms. My arms
ached for days afterwards.
Some people recommend pushing and pulling the sander. We would let the sander
pull itself forward, until it bumped the wall, and then pull it back. On the
forward stroke the machine was barely pressing down, but on the back stroke we
would lift up to apply pressure. This allows a brief moment to rest one's
After going over the floor the first time, we found many high spots, so we
had to do another complete diagonal sanding.
After the diagonal sanding had removed all the height
differences between the boards, we sanded the floor again using the
coarsest sandpaper, 20 grit.
This sanding must be continued until no more diagonal scratches are
As the sander is dragged backwards, the operator eventually hits the wall
with several feet of floor remaining. The approach is to work right-to-left
across the room, then turn around and sand the missed section, from right to
left, back to the starting point.
A fundamental problem of this unavoidable approach is that when the sander is
stopped, it digs into the floor slightly. So in the middle of the room we had a sea
of slight waves. These can barely be seen... until the floor is finished
with a coat of urethane. Then the waves show up great.
Changing The Sandpaper:
Changing the sandpaper on the Silver Line drum sander is
kind of a pain in the neck.
The front housing tilts up to provide access to the drum.
The drum is rotated until the seam in the paper is up front.
Of course, unplugging the sander is critical. If this machine
were to accidentally start, it will sand your fingers down to little tiny
We used a pair of wrenches to turn the clamping devices.
On the front of the machine, above the rubber bumper, there
is a long tray, which looks sort of like that map pocket on the
door of your big 'ol SUV.
This is used as a folding guide, to make the proper end fold in
the sandpaper sheets so they fit into the drum just right.
These are not the ordinary 9" x 11" sandpaper sheets that you buy
at your local hardware store. They are specifically made for floor sanders, and
all rental shops should have a supply of sheets that they will sell you. Our
shop sent us home with a couple of each grit, and they gave us a refund for the
sheets we didn't use.
Which brings up an important point: There is a good chance that a
sheet will get ripped during sanding, so having extra sheets on hand is a good
idea. In our case, the house is 15 miles out in the country, and we did this job
starting on a Friday afternoon and wrapping up on Saturday morning. It would be
a real disaster to have the sandpaper rip into shreds just after the rental shop
closed. So we got extras of all the grits: 20, 36, 60, 80 and 100.
To install the new sheet, one end was placed into the slot
and the drum turned by hand to wrap the sheet around.
The other end was pushed into the slot.
That shiny metal piece with the arrow... that is the end of
the clamping device. There is another one on the opposite side of the
When those square shafts are turned in the direction of the arrows,
they pull the paper into the drum.
A wrench is used to tighten the clamping mechanisms. I
believe it required a 1/2" wrench.
Sometimes we were able to tighten the paper by turning one clamp at a
time, sometimes we had to turn both simultaneously.
We did have some difficulty getting the paper installed tight. It often took
several attempts, and sometimes the paper would be loose on one end of the drum,
which I figured would lead to premature ripping.
Cleaning Up The Perimeter Of The New Wood Floor:
After sanding with two grades of sandpaper, it was quite
evident where the drum sander's work ended... a very distinct line about 4
inches from the wall.
The power edge sander is necessary to sand down this edge
This tool is basically a very beefy 7 inch disc sander, and the same
grits as the drum sander are used. We found that a circular looping motion
worked better than simply running the machine along the wall.
We used the edger for the entire closet, because the boards were oriented the
wrong way for the drum sander. Sanding the closet didn't take very long.
We developed a routine, one of us running the drum sander, and the other
going around the room with the edge sander. Luckily the room had outlets on two
separate circuits, because each of these machines has a motor rated at 15 amps.
Many motors rarely draw their rated current, but the drum sander does.
Several times when I started the machine it tripped the 15 amp circuit breaker.
I found that I could roll the drum a little by hand and try starting again, and
it would work just fine, after I reset the breaker.
Some Thoughts On This Puzzling Behavior:
Humans Voluntarily Sanding Floors
This was the only the second time we have used the rental floor sanders. I
didn't really remember anything negative about floor sanding until we started
this second room. And then it all came back to me. This is really a form of
punishment. This is not a hobby... nobody would do this if they knew what they
were getting themselves into.
Or maybe I'm just not a big enough guy. I'll admit I'm smaller than the
average bear, maybe smaller than the average adult male too, at only 165 pounds.
The drum sander is certainly made for a much larger species. Maybe it is
intended for the Neanderthals among us, or maybe some people have trained
gorillas to run these drum sanders.
After running the drum sander for about 8 hours, I went to bed sore and
tired. The next morning I ached all over. I should have followed the advice on
the TV commercial: Take some Advil and use those stiff aching muscles.
By noon on Saturday I was ready to return the beast to the rental shop. We
stopped sanding at 80 grit. We never touched the 100 grit paper. There were
still some high spots around the door that were hard to reach with the edge
sander. We had left the door in place to keep the dust out of the rest of the
house, which worked well.
Saved By... The Inexpensive Power Tool
Owning a 5 inch random orbital sander, I figured I could use
this tool to touch up some problems areas.
The 5 holes in the disc allow the sander to pick up much of the dust.
There were several problem areas:
- The wave zone in the middle of the room, caused by stopping the sander
momentarily to reverse directions.
- The edges. The power edger does a poor job of blending in with the drum
sander's work. The result is a definite hump a few inches from the wall, all
around the room.
- The corners. The 7 inch disc cannot get close to the corners.
- The area around the door that was hard to reach with the power edger.
The 5 inch random orbit sander solved all of these problems. I started
by purchasing a large quantity of 60 grit hook-and-loop (a.k.a. Velcro) discs,
as well as some 100 and 150 grit discs.
I began with 60 grit, which meant that our earlier 80 grit sanding was
- For the wave zone, I sanded in large blocks, about 2 feet square. I ran
the sander over and over, side-to-side and up-and-down, randomly and in
uniform patterns. Since the small sander can be run with one hand, I could
feel the floor with my other hand. After about an hour of sanding I had the
wave zone pretty much flattened out.
- Along the edges I ran the orbital sander in loops and circles, feeling the
smoothness as I progressed. In about an hour I was able to vastly improve on
the results of the rental tools.
- While sanding the edges I spent a few minutes getting into each corner.
Since the random orbit sander is round, it cannot get all the way into
the corner. But it made a big improvement over the power edger. The
remaining high spots in the corners can be scraped out with a chisel or
paint scraper, and hand-sanded smooth.
- The high spot around the hinged side of the door. For this I removed the
door (the fan drew the air into the bedroom, keeping almost all of the dust
out of the adjacent dining room) and attacked the hump. At first I thought it would
take an hour for this hump, because it felt like it was 1/4" high. But
after maybe fifteen minutes I had the hump evened out.
So this little $60 Porter-Cable random orbit sander ended up being the hero
of the story. Sort of a "David fixes Goliath's shortcomings" tale.
This tool is worth it's weight in gold. Porter-Cable deserves a "Golden
Hammer Award" for their fine product.
Then I went over the entire floor with 100 grit sandpaper. I was considering
doing a pass with 150 grit, but decided that would be overkill. For fine
furniture, yes. For a floor, no.
Using A 3-Head Random Orbital Floor Sander
In the decade since I first wrote this article, I have installed 4 or 5
rooms of new unfinished oak flooring, and I have refinished half a dozen
rooms with urethane-coated hardwood floors.
And since doing this floor in 2001, a
new machine has appeared on the market: The Varathane ezV 3-head
random orbital floor sander. This machine is intended for
refinishing old wood floors, but it also works on new wood floors in
First, there can't be any significant height differences between
adjacent boards, like we had here. These small "steps" would tear up
the sandpaper and possibly the backing pads that hold the
I would say that any "step" of 1/32" or less would
probably by acceptable, as long as you sanded with caution and were on the
lookout for small shreds of sandpaper being torn off the sanding discs.
The first time I rented the Varathane ezV floor sander, I had just
installed two rooms of white oak flooring in this same house. The flooring
was much higher quality than the stuff used here. Actually, the flooring was
milled to be prefinished (but we bought it uncoated), so
the edges had the "micro-bevel" that hides any unevenness between boards. To
smooth out any variations in height, I used the ezV sander but skipped the
coarse sanding (36 grit) and proceeded with 50 and then 80 grit. This floor
sander worked great to eliminate the numerous slight high spots in the
floor. I smoothed out 350 square feet of flooring in about 4 hours.
I mention this little story because it raises a worthwhile point: If new
hardwood flooring has a lot of high spots or "steps" between boards, the
best approach to sanding would be to use a drum sander with 20 grit
sandpaper to grind down the wood until the steps are gone, then sand the
floor with 36 grit sandpaper, and THEN use the ezV random orbital
sander starting at 36 grit and proceeding to 50 then 80 grit. This would
solve the problem of the waviness that is difficult to avoid with drum
I would describe the rental drum sander and power edger as the Brute Force
approach to floor sanding. It's a very aggresive machine, which is
needed when the flooring is not very precisely milled. The drum sander may also
be the best tool for refinishing an existing wood floor that is badly gouged. I
like doing projects myself, but I would seriously consider hiring a professional
if drum sanding was needed... someone whose body is accustomed to the abuse
dispensed by these machines.
I guess the hard work in sanding this floor is really just a testament to the
lack of precision that is standard in the flooring industry. But then, we bought
our flooring from a small local sawmill. What can anybody expect? When dealing
with wood, precision is hard to achieve.
Or is it?
Since doing this flooring job, I have installed three rooms of pre-finished flooring,
some normal 3/4" thick, some thin 3/8" thick. This material is just
like installing normal flooring, but when the boards are installed the floor is
done. It really hastens the pace of a project.
Most pre-finished hardwood flooring has a coating of aluminum oxide, which is
the same material that most sandpaper is made from. These floors resist
scratching very well, but they are still prone to denting and water damage. One
possible drawback is that when it comes time to refinish the floor, you can't
simply sand down the surface because the coating is just as hard as the
sandpaper. Supposedly there are special chemicals available that soften the
aluminum oxide coating and allow for refinishing, presumably with a conventional
Was all this labor worth it?
Floor Sanding, by Don Bollinger, Fine Homebuilding's Builder's
Library series, Taunton Press.
Originally published in Fine Homebuilding magazine, April 1983
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