Did you know that refinishing a floor means that you’ll sand over your floor multiple times?
Some first-time sanders believe that they’ll just use one grit of sandpaper and sand over their floors one time and, voila!, the floors will be clean, flat and smooth.
But the sad truth is that sanding is not like renting a Rug Doctor—it will take at least four passes, each with a progressively finer level of sandpaper, to truly refinish most old floors.
And the hardest thing you’re going to do on the project is to determine the perfect grit starting pass for your floor. But we can help you figure it out.
Most people who have never sanded a floor before assume that every floor is sanded with the same grit sequence.
If we had a dollar for every customer who insisted that all floors only three grit passes we would have lots of dollars. But every floor is different and the condition of your floor will determine how you sand it.
And you can’t start sanding until you figure out the right starting grit.
Pete’s carries SEVEN different sanding grits for sanding floors, but not every floor needs all seven grits.
The more damaged your floor and the harder the wood species, the coarser your first grit pass will be.
Here is a rough guideline for what the various grits do:
12grit (available for edgers only)
Starting grit for floors with heavy adhesive or multiple coats of floor paint.
Starting grit for floors that still have finish or haven’t been sanded for 30 years or more.
24grit is the recommended starting grit if there is sander flaw in the floor from previous sandings or obvious foot-soiled areas where old finishes have worn through to wood.
Never a starting grit – 60grit takes out 36grit scratch, but it does not remove wood or finish.
Takes out 60 or 80grit scratch. Final grit for birch and maple floors and any floor that will be stained.
Assess honestly, sand appropriately
The most common mistake we see in floors done by do-it-yourselfers is timid sanding: a floor that still looks dingy because it wasn’t sanded aggressively enough.
So, the more honest your assessment of the condition of your floor, the more willing you will to accept how much work it will take to renew your floor.
36grit is your testing grit – it will help you determine the finest starting grit that will work for your floor
If you think your floor is in pretty good shape, put a 36grit belt on the drum sander and sand a small test area, about 4’ x 4’ (pick an area of the floor that is in rough shape, not one of the spots that still looks good).
Stop the sander and carefully inspect the area you just sanded.
If that section of floor looks completely bare and clean, even at the edges of the boards, then you have successfully determined that the grit sequence for sanding your floor is 36grit, 60grit and 80grit.
If the area you tested is not completely clean, then you have determined that your floor will need MORE than just that 36-60-80grit formula.
So, pick a new spot on the floor (again, preferably a spot in bad shape) and try a more aggressive test. For example, if the first test left just small amounts of finish at the very edges or centers of the boards, then your next test might be to cross-cut at 36grit followed by a straight pass at 36grit. Read our “Magical Exception of Cross-Cutting” info below.
Look at your sanded test area.
Is it bare and clean? If yes, then yay! You’ve determined that your sanding sequence is 36grit cross-cut, 36grit straight, 60grit and 80grit.
Most floors in the Twin Cities were installed prior to 1950 and will need a 24grit start when using a 110v sander.
Think your floor is in bad shape? Don’t bother with the 36grit test – begin testing with a 24grit – 36grit combination.
What if it fails that test?
Keep testing with more aggressive combinations until you find one that gives you clean wood by the time you reach 36grit.
Don’t bother testing 60grit or 80grit – they are not designed to remove finish or wood fiber. We already know that they will adequately remove scratch from 36 grit, so limit your testing to figuring out your starting point.
The magical exception of cross-cutting
If you have the reverse—a severely scarred, uneven, water-damaged or painted floor—then you may want to consider not only starting with a coarse grit, but sanding at an angle to the grain.
This is an important exception to the rule of always sanding with the grain of the wood.
It only applies during the rough sand stage, but it is a very efficient way to speed the process of cleaning and leveling an old floor.
Because of wood’s natural tendency to shred and splinter when it is sanded off-grain, the sander can remove more wood with the same amount of effort when positioned at an angle. The angle does not need to be drastic; sanding just 10-15° off parallel is enough.
The downside of using this procedure is that, after you make an entire pass at an angle, you must follow it with another pass parallel to the grain at the same grit. So, if you do a 24-grit cross-cut pass, your sanding sequence would be 24 diagonal > 24 straight > 36 > 60 > 80.
Newly installed floors can be rough-sanded with 36-grit parallel to the grain.
The rule to remember is that, no matter what grit you choose as your starting point, you must sand, in order, with every grit that is finer than your starting point.
So, if you start with 16-grit, you cannot jump to 36-grit; you must go 16 > 24 > 36 > 60 > 80 on both machines.
If you start at 24-grit, you cannot jump to 60; you must go 24 > 36 > 60 > 80 on both machines.