Secrets Of a Floor Refinisher - continued
The Art of Sanding
When I sand a floor, I’m mainly trying to remove old
finishes and stains. I don’t want to remove any more wood
than I have to. Most things in construction you can fix —
you can touch up paint, and you can patch drywall. But once a
wood floor is sanded, you can’t put the sawdust back.
That’s gone forever.
Most floors have a life of two or possibly three refinishings.
After that, there’s nothing there. With 3/4-inch
tongue-and-groove boards, when you wear down almost through the
top lip of the groove, the lip starts to lift and people start
to get big splinters. It’s over.
You’ll sand a floor several times each time you refinish
it. It starts with a diagonal cut, using rough grit, to level
up the boards. There’s usually a second diagonal cut at
right angles to the first. Then it takes one or two straight
cuts (parallel to the boards) to smooth the surface, using
progressively finer grits. Finally, you screen the entire floor
with the finest grit to create a consistent fine scratch
Nitty gritty. You always
step from coarse grit up to fine grit, but the particular grits
are different for different cases. You have to get a feel for
it — going too coarse burns up too much wood, but going
too fine burnishes the wood and can make it reject the
The lowest grit we have is a 12. Twelve-grit means there are
12 pieces of grit per square inch of paper, so your grit is far
apart and pretty thick. A 120-grit paper has 120 pieces per
square inch; that’s a fine grit for floor sanding.
A 12-grit paper is like gravel. I wouldn’t hit wood with
12-grit — it’ll shred it. But I would use it to
tear off linoleum and tar and paint. Linoleum dust is nasty,
but you can tear off linoleum in big chunks using a 12-grit
belt. Old linoleum is often sealed down with tar, but if you
move fast with a coarse grit, that will come up in chunks with
the tile, and you can sweep it up.
If you start with a 12-grit, you’ll step up to a 36 or
so next. Why just a 36? Well, you’re trying to match what
came before. You can’t jump from a super-low-grit paper
up to a fine grit in one step. A 100-grit paper would just clip
the ridgetops off whatever the 12-grit left behind and leave
the grooves there. You want to use a grit coarse enough to cut
a lot off the high points, without digging any new low
For a bare wood floor, or one with nothing but old finish on
it, I’d start out higher than 12 to begin with. Take a
brand new oak floor, just installed. A good first cut would be
a 40-grit on a diagonal; then I’d do a 60-grit straight
cut, an 80-grit straight cut, and finally screen it with a
100-grit screen — or even just another 80. But if
you’re working with a sappy old fir floor with varnish on
it, you might go down to a 36- or even a 24-grit for the
diagonal cut. Then you’d step up to maybe 40 and 60 for
your straight cuts, and screen it with — at most —
an 80-grit. Use fine grit on a fir floor, and your belt will
instantly load up with sap.
Diagonal cuts. Your first
diagonal cuts bring the board edges even. Boards are often at
slightly different heights, so if you ran parallel to the
boards, it would put the drum off kilter and keep you from
sanding smooth. So I make a diagonal cut first, and get down to
bare white wood.
In some old houses, you can encounter pine floors with boards
more than 22 inches wide. Often the boards are cupped —
some concave and some convex. In a true restoration you
don’t level those out — you hand-scrape them
On a newer house with a wide 1x6 or 1x8 pine floor that had
some cupping, I might need two diagonal cuts to get it level.
If the boards were convex, the center of the board would get
cut first; if they were concave, just the edges would get cut.
All along each board you would be able to see parts that were
still untouched (Figure 3), so I’d make a second diagonal
crosswise to the first one, to get the boards down level for a
flat surface. (By the way, if it’s the edges that are
high, you may want to hand-scrape the floor or leave it alone.
If you grind down just the edges on your early passes, you
might end up exposing the tongues before you get the boards
Figure 3.A first rough cut with the drum sander
using coarse grit can pull off linoleum and its adhesive but
may not expose the wood in low spots (left). The drum sander
also leaves an unsanded area near the walls (right), which has
to be sanded with the edger.
All around the perimeter, the first cut leaves a margin
that’s still the original color, because the drum sander
can’t reach all the way to the wall. We have to hit that
with the edger next.
Once the whole floor’s down to fresh wood, it gets
harder to see where you’ve sanded and where you
haven’t on subsequent cuts. The trick is to get a
carpenter’s pencil and go around the whole perimeter of
the room and scribble like crazy over about an 18-inch margin.
Anywhere you don’t hit on your straight cuts,
you’ll see pencil and you’ll know you have to edge
Straight cuts. After the
diagonal cuts and the first edging, it’s time for a
straight cut (Figure 4). I will hit the wood with two grits,
but I don’t like to start out any coarser than I have to.
I always experiment first — take an old belt out of my
truck, say a 50-grit, and put it on my drum. If it cuts the
floor perfectly white, that’s the lowest I’ll go;
then I’ll step up to an 80.
I never go above 80-grit. I won’t use a 100-grit belt
— all it does is burnish the wood, preventing it from
taking the stain or finish properly.
Figure 4.Straight cuts parallel to the boards
using grits as fine as 80 create a flat, smooth surface that
will accept stain. It’s important to wear hearing
protection and to keep the power cord out of the way of the
Feathering. When you start
each pass with the floor sander, you feather it gently down
onto the floor as you move forward. The belt pulls the machine
forward, and as you approach the wall you ease the machine back
up, like taking a boat out of the water. Then you ease it down
again and pull it all the way back in the same track. Now move
it over and repeat the process, overlapping each track just a
Most sanders cut an 8-inch path. With 1x3 strip flooring,
which has about a 2 3/4-inch reveal, I like to line up and take
two boards at a time. On each successive course, I overlap
about two thirds of a board. It keeps me straight and blends
At the end of each stroke, the machine will get within 6 or 8
inches of the wall. But you have to start each stroke 4 feet
from the wall, because you’re standing behind the
machine. To hit that 4-foot section, you have to turn the
machine around and go the other way. Instead of starting the
same distance from the wall each time, however, I like to
stagger my cuts. I’ll start one stroke 4 feet out, the
next 6 feet out, the next 5 feet out, and so on. Or I’ll
just start in the middle of the floor, and stagger randomly.
When I turn around, I’ll feather into each cut where I
started the last one. This breaks up the pattern. Otherwise,
the transition between the two sections that you sanded going
in opposite directions will be clearly visible in the finished
That visual pattern is caused by the way the sanding belt
pulls on the wood fibers. It’s called a corduroy effect
because you can see the same thing on a pair of corduroy pants.
Run your hand over the nap one way, and it will look one color;
rub it the other way, and it will look darker or lighter. Just
like fibers in cloth, wood fibers will lie one way or the other
depending on which way the belt pulls them. You can’t see
it in the raw wood, but when the finish goes on, it jumps out
and you can’t miss it.
Where the big machine can’t get to the wall, you have to
edge. You don’t just stab the edger in and out of the
wall; you move it along the wall in circles, like waxing a
You have to stoop over to operate the edger (Figure 5). If you
do it hour after hour, it’s pretty hard on your back. I
like to keep my legs spread as far as I can and brace my elbows
on my knees. That takes some of the strain off the back.
Figure 5.When operating the edger, the author
rests his elbows on his knees to reduce the strain on his back.
The edger is moved in a circular motion.
The whole 7-inch disk doesn’t contact the floor —
just the front inch and a half does. An edger doesn’t sit
flat on the floor; it’s tipped up. The wheel height is
adjustable to vary the angle of the disk. It’s crucial to
learn how to adjust the wheels, because if those wheels are too
high, the front of the disk will gouge the floor; if
they’re too low, the disk will clog up and won’t
As I work the edger in and around, in and around, I’m
cutting my pencil marks, so I know that the margins are now
level with the center of the floor. Then I pencil it again, and
do my final straight cut. After sanding and edging one last
time with a 60-grit or an 80-grit at most, I’m ready to
vacuum again and screen.
The buffer’s job is to create a uniformly scratched
surface over the whole floor, blending the different patterns
created by the other equipment (Figure 6). If the last grit on
the drum sander was a 60, I’d buff with an 80-grit
screen; if the last grit on the drum sander was an 80-grit
screen, I’d screen with a 100-grit. You should keep the
buffer as flat as possible so as to buff evenly; if the buffer
leaves swirl marks, you’re holding it at too much of an
Figure 6.The buffer sits on a synthetic fiber pad
and a sanding screen and sands with a circular motion. The
whole screen should contact the floor as evenly as possible to
create a uniform scratch pattern with no visible swirls. An
80-grit or, at most, 100-grit screen should be used to leave
the wood rough enough to absorb stain and finish.
It’s really important to vacuum before and after each
sanding or screening. Otherwise, the screen or paper just rides
around on sawdust and doesn’t scratch the floor. By the
same token, there’s no point using too fine a screen. The
finest sander belt I’d use is 80-grit; the finest buffer
screen would be one step higher: 100-grit. Anything finer just
burnishes the wood, fills the fine grooves, and prevents the
wood from accepting stain or finish.
Once the wood is clean and smooth, it’s time for a stain
and a finish. In a future article, I’ll discuss the finer
points of coating a wood floor.Sean Barryran a professional wood floor refinishing business in New
England for 25 years. He is now the proprietor of the Music
Store in Great Barrington, Mass.