Sanding a wood floor is a multi-step process.
That way you'll get a heads-up on, and hopefully the knowledge to avoid, some of the problems you might encounter and some of the mistakes beginners make.
The 13 steps to sanding your floors:
- Determine your grit sequence.
- Sand all main field areas with the drum sander on the first grit of your determined sequence.
- Use the edger (using the same grit you just used on the drum) to sand all the areas that the drum couldn’t reach
- Sweep or vacuum all sanded rooms
- Sand all main field areas with the drum sander on the next grit in the determined sequence
- Use the edger (using the same grit you just used on the drum) to sand all the areas that the drum couldn’t reach
- Repeat steps 4 through 6 until you have sanded the entire floor through 80 grit (or 100 grit for maple floors or oak floors that will be stained).
- Use a radiator edger to sand under all radiators or toe-kicks if you have them.
- Scrape or sand all corners and around radiator feet or pipes.
- Examine perimeter of all rooms and remove any visible edger swirl by hand-sanding.
- Use a pole sander or a buffer over the entire floor at 100 or 120grit to blend the straight sanding cut from the drum with the circular sanding cut from the edger.
- Vacuum the entire area thoroughly. Vacuuming twice never hurts and usually helps.
- Use a dry microfiber cloth or other clean, lint-free textile to remove all remaining dust from the floor.
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 and 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
- 16grit: starting grit for floors with heavy shellac finishes or single layers of paint and sometimes for very old, hard maple floors (this is an unfortunate but common starting grit here in the Twin Cities,as you can see in the photo at right)
- 24grit: 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
- 36grit: starting grit for floors that are newly installed or have very minimal finish. Every trace of finish should be gone from your floor by the time you finish with this grit.
- 60grit: Never a starting grit – 60grit takes out 36grit scratch, but it does not remove wood or finish
- 80grit: takes out 60grit scratch, but does not remove wood or finish –Final grit pass for most American hardwood floors
- 100grit: 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 3 grit 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” 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.
Choosing your abrasive
As mentioned, doing a professional job on your floor will probably entail four sanding passes, but you do have some flexibility in choosing the abrasive for your first pass. The five grits of abrasive available for the drum sander are 16, 24, 36, 60 and 80. The grits available for the edger are 12, 16, 20, 36, 60, and 80. Most floors in the Twin Cities were installed prior to 1950 and will require a starting grit of 24. If your floor is newer and you are convinced that you do not need to begin that aggressively, do this test: put a 36grit belt on the machine and go to the worst section of the floor. Spend 5-6 minutes and sand a 7' x 8' area. Now, turn the machine off and look at that sanded section. If you can honestly say that there is no finish left on that floor and that you cannot feel the board edges when you run your hand across the wood, then you can proceed to sand with 36grit, proceeding through 60 and 80. But if there is still visible finish in the test area, you are better off doing a fast pass at 24grit to get the bulk of the finish off before changing over to 36grit and removing every last bit of it. Remember, 60 grit and 80 grit are not designed to remove finish—all they do is smooth out scratches.
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 24grit cross-cut pass, your sanding sequence would be 24 diagonal > 24 straight > 36 > 60 > 80.
Newly installed floors can be rough-sanded with 36grit 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 16grit, you cannot jump to 36grit; 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.
For each grit pass you make on your floor, you will begin with the drum sander. Make sure you read Working with sanders and edgers.
Don’t just sand one room at a time – sand everywhere the drum can reach in every room in your project.
If you’re sanding floors on two different storeys, do everything on the upper level first and then sand downstairs; you only want to haul those machines upstairs one time.
If you have the luxury of having two people on the project, one on the drum and one on the edger do not use both machines in the same room at the same time! This is a safety issue; it is much too easy to be focused on your machine and not see the cord of your partner’s edger. It is better for the drum sander to go first, finish that grit in the first room and proceed to the second, and then let the edger begin, alone, in the first room once the drum sander has moved on.
Step 3: Use the edger (using the same grit you just used on the drum) to sand all the areas that the drum couldn’t reach.
For every grit you do, drum first and edge second. This is largely because the edger can sand out drum marks that you might leave during the transition at the wall edge.
In older homes, where there has been significant foot traffic in the main field of each room, but no wear at all around the perimeter, you may find that there is a whole lot more finish around the edge. So, don’t be distressed when you switch to the edger and use the grit that was working just fine in the middle of the floor and find it clogging up and glazing almost immediately. Just drop down to the next coarser grit on the edger only. Move quickly and use that coarse grit to remove about half of the finish. Then continue with the grit you were supposed to use that matches the drum sander pass you just finished –now the condition of the edge area matches the condition of the field and you can proceed with your planned grit sequence.
Every time you finish a grit you need to vacuum, or at least sweep all the surfaces you just sanded. This is because the pieces of sanding mineral fall off the abrasive and litter the floor after every grit pass. Even though you may have moved on to a finer grit, those big, coarse particles from previous passes are still being driven into the floor by your drum and edger. Even under your fine paper, they continue to grind their 16 grit cat-scratch into the floor, and you will wonder where all those big, deep gouges are coming from.
Once you’ve vacuumed, you’re ready to begin again with the drum on the next, finer grit step in your sanding sequence.
Step 6: Use the edger (using the same grit you just used on the drum) to sand all the areas that the drum couldn’t reach.
Hopefully, this is self-explanatory by now.
So, now you’ve established your pattern, it’s just a matter of sanding without skipping grits until you reach either 80 or 100grit. 100grit is the recommended finishing grit if you plan to stain your floors, or if you are sanding a maple floor. In both those cases, particularly on the edger, you need to work harder to make sure that all evidence of your sanding is removed, which is easier to do when you can sand to a finer grit.
Why is maple different?
Maple is so hard and dense that any scratch left in the wood is held cleanly and crisply. Those crisp incisions make a snug little crevice for stain, or even natural finishes to accumulate. Once you have pigment or product built up in that scratch, it because twice as visible, particularly the curved scratch from the edger. Sanding through 100grit makes the scratches smaller which means they can’t hold as much color and are easier to camouflage.
As your floor gets progressively cleaner, it gets harder and harder to tell where the sanders have been. Remember, you’ll have at least TWO sanding passes (60grit and 80grit) where you will just be polishing out scratches – there will be no finish to serve as a tracer. So, we recommend using a series of light pencil lines drawn directly on the floor before you begin 60grit and again before you begin 80grit. The drum sander will erase any pencil lines it touches and the lines that remain will show you exactly where you need to edge. When all the pencil lines are gone, you’ll know you haven’t accidently skipped any areas of the floor with your big machines.
You’ll get a better blend with the cut from the drum sander and edger if you sand your radiators or under your toe-kicks after all the other sanding is done. This also keeps your rental of that extra sander down to an absolute minimum.
Edgers are round, but rooms are square, so you’ll need to do something in the four corners of every room, closet or stair tread In your project. Carbide scrapers are great, but can be expensive. Carbon steel scrapers are cheap and work well, but you’ll have to keep sharpening (often once for every corner) because carbon steel dulls quickly when you’re scraping finish. Multi-tools (like the Fein or Bosch) have small, triangular sanding heads that also work well. If you scrape your corners, sometimes you can leave them too smooth; take a folded piece of 80grit sandpaper and lightly sand over where you’ve scraped to reopen the wood grain so it matches what you did with your other sanders.
No matter how long you have been sanding floors, no matter how skilled you are with the edger, there will still be edger swirl left around the perimeter of your room, even after you finished sanding through 100 grit. And even if you didn’t skip any grits! After you finish your final edger pass, you should inspect the entire perimeter of your project on hands and knees and with a flashlight if necessary to locate every last bit of visible sanding scratch from the edger. When you find it, remove it by hand-sanding with 80 grit. Don’t be tempted to go get your palm sander! A palm or orbital sander is more powerful than your hand and will so over-polish the floor that, while the swirls will be gone, the texture of that area will be much smoother and more closed than the areas that were done with either the drum or the edger. These areas will not allow finish to absorb as easily or deeply and will have a distinctly different tone than the surrounding floor.
Step 11: Use a pole sander or a buffer over the entire floor at 100 or 120 grit to blend the straight sanding cut from the drum with the circular sanding cut from the edger.
Do you know how, when you look at the outfield at a baseball game, they stripe the field just by mowing adjacent areas in different directions? Unfortunately you can get the same effect on your sanded floor, only it doesn’t look quite so cool. The place where the straight scratch from the drum sander meets the circular scratch from the edger can show up as a line, just as distinct as one of those outfield mowing lines. And what’s worse, you won’t see it on the freshly sanded floor; it only becomes visible AFTER you’ve applied a coat of finish. Once that coat of finish is down, it takes a lot of work to fix this problem, so the idea is to prevent it from happening in the first place. And prevention is easy, but it needs to happen just as you are at your most exhausted. But before you begin your final cleanup, you need to use a pole sander or a buffer to do one final, blend-sand over your entire floor. Using 100 or 120grit, you will put a shallow, but most importantly uniform scratch pattern over the entire floor. This will fool your finish into believing that only one machine left its mark on your floor and it will absorb uniformly into the wood and will look consistent and blotch-free everywhere.
Getting all the dust off is more important than we can ever say. Pay particular attention to the dust in the cracks between the boards and at the very edges of the room, especially the gap under the baseboards. Finish has a way of finding little hidden pockets of dust and pulling it up and spreading it along with your mop head. Try not to use the plastic wand on your shop vac – it can leave plastic residue marks where it scrapes on the floor. Find a vacuum wand with strong, soft bristles.
Step 13: Use a dry microfiber cloth or other clean, lint-free textile to remove all remaining dust from the floor.
Many people would use a commercial tack cloth for this step, but we don’t recommend it.