The 2 Biggest Mistakes DIY Floor Sanding Enthusiasts Make

I regularly have customers that have tried to sand their floors, made a right pig’s ear of it and have then called me in to correct it.
The first mistake that people make is they think that floor sanding is simple! Well, it is when you know how! They think that because they applied a bit of sandpaper to a piece of wood in woodshop class, they know how to sand a floor like an expert. How hard could it be? This is a question I get from some friends. They think there’s nothing to it, just gotta sand it down and lacquer it.

Well, unfortunately, it doesn’t quite work like that. For one thing, it would take a very long time to do by hand and therefore must be done by machines. Namely, very heavy powerful machines. Without experience or some guidance with these machines, there’s a very high chance you are going to do a poor job. Do some research (on this website!) and make sure you know everything you can know before taking on the task.

The second mistake I see time and time again is that people think that they can sand a floor starting with 120g sandpaper. They are too concerned with not removing too much wood that they end up not even taking all of the previous finish off! The floor looks nice and clean so then they put down their lacquer or oil or varnish and BAM, that’s when they see all the previous finish that hasn’t been removed from the floor. As they apply the new finish, it reacts differently on areas where there is bare wood and the areas where the previous finish is still on the floor.

I have seen this turn floors GREEN!

Just so you folks know, I have a very heavy powerful floor sanding machine. I almost always start with 36 grit. Rarely I will start with 60 grit because the floor is quite smooth and there’s not much damage. Once in a blue moon, I will start sanding with an 80 grit. What are the conditions needed for me to start with an 80 grit? It needs to be a very well laid, unfinished floor. If your floor has the normal wear and tear and a previous finish, there’s a good chance you are going to need to start on a 36 grit sandpaper.

Be sure to check out How To Use a Belt or Drum Floor Sander so you don’t make common mistakes when using a floor sanding machine.

P.S There is a video on youtube about “how to refinish a hardwood floor” and it has over 300,000 views. And it is dead wrong! He recommends using a finishing machine. A stand up orbital sander that should only be used to smooth the floor after the initial sanding. I have had customers that have used this on newly laid, unfinished floors and after spending DAYS on it, they call me up because they can’t get it smooth.

These machines are not made for removing lacquer, oil, dents or scratches. They are made for smoothing the scratches from 100 or 120 grit sandpaper on a belt sander! So the floor needs to already be clean and flat and very smooth in order for these to work. Such a shame this video has become so popular!

Don’t fall into these traps guys, get prepared.


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  1. Hi..
    I want to leave nail holes unfilled in my wooden tongue groove floor boards, think it will look better than filled, anyone done this? how do i stop getting divits at each nail hole after varnishing.
    Anyone done this id be interested how you got on.

  2. How do you know if your floor boards are good enough to be used without carpet/good enough to be sanded and finished?

    1. I think the visual appearance makes a big difference. Are there lots of repairs? are there boards that have already been replaced with new cheap pine? also, if you bounce on the boards between the joists, is there a lot of movement? if there is, skimming 1 or 2mm off the top may make it even more flexible and unsuitable as a floor.

  3. I’ve made the mistake of using a drum sander at 40 grit and adding extra weight just to remove the laquer of the previous coat. Problem is – it’s left “roller” marks all over the floor… now I’m trying to figure out how to remove them before getting into the finer grades. Should I just go over the whole floor again at 30degree angles at 40 grit?

    1. Hi Tim. I’m glad that you have taken on the challenge of using a drum sander! Try doing the 30-degree cut with a 60 grit and persevere. You will find that the diagonal cut will remove the old drum marks but put in new diagonal ones. So if you do it with 60 grit you are progressing. Then you do 80g straight, which removes the drum marks from the 60, each time getting flatter and flatter and closer to the goal. I hope that works!

  4. I have a 15″x16″ cat urine stain. What needs to be done to eliminate the stain? Thank you.

    1. The surest thing to do, and what a local floor team would do, is cut those boards out and replace them. This way there is no issue at all. If you can’t do that then there are guides on the internet for using hydrogen peroxide to remove the stains. In my experience though, it tends to leave a patch in its place, sometimes slightly lighter than the wood around it. Not as bad as the urine stain but still a visible patch

  5. Hello, thank you for this info! I have lovely old-growth red fir floors that were installed in 1892, which I found buried under 1970’s green shag carpet in our new (historic) home. There were some large cut-outs in the floorboards, filled in with plywood. I had an experienced carpenter remove the plywood and thread in salvaged red fir of the same age. Now I’m attempting to use an American Standard square floor sander, which Home Depot says is the most forgiving for beginners. My concern is there are minor differences in heights of the some of the aligning threaded boards, some are 1/2 mm to 1 mm taller than the others, and I’m hoping to sand them flat. However, because fir is soft wood (albeit old growth with tight grains making it harder), I was told not to go rougher than 60 grit. That’s also due to the age of the boards, with concern that it may have already been sanded a few times. Any thoughts on that? I probably should have contacted you sooner – I am starting today. I’ll take the advice of starting with 120 until I get the hang of it. Thank you! – Liz

    1. you will deffo need 36 grit to get this flat. Pines are just as hard to sand as oaks, while its softer its more fibrous and resilient. I think you will find you will be strugling even with a 36, it will just need a good going over a few times to get it clean and flat – probably

  6. Hi Ben,what stage would you putty any it before the start of the sanding process..I’ve got 90m2 of engineered American Oak to resend & polish..
    Great info by the way

    1. are the dents that deep that they need putty? maybe soak the dent with water let it dry, and again, to get the dent to swell. or even better steam it. This should raise the dent, then sand it so its just clean wood instead of filling. If it’s a no go then just fill it before the final sanding

  7. Hi Ben,

    We have a bit of a predicament. We have a parquet flooring with 3-4 mm of oak wood. The sanding company said they can sand it back (both companies in fact) with no issue, though won’t guarantee the work. A builder (friend of theirs) came in to look at repairing a few boards and is now saying not to sand it back as he would be concerned of cracking due to some flex in the board and the 3-4 mm only available. He is suggesting new floor entirely which we can’t afford right now. The sander is now getting nervous about sanding but is saying he is happy to do it still. Have you heard of boards cracking or splitting after they have been sanded back? We’re not sure what to do at the moment. Chris

    1. boards don’t generally crack or split due to being sanded too thin. What usually causes that is massive swings in humidity, like turning on underfloor heating from full blast. it should be fine, I would suggest using an acid cure lacquer to prevent problems though. When the wear layer gets thin and you use a waterbased lacquer, the moisture can expand the surface, curl the edges and all sorts of trouble. Usually its fine, but just to put your mind at rest, use an oil based lacquer

  8. Hi Ben, I’m sanding my floors and have been using a U-sand random orbital sander and it is just not aggressive enough for my floors. They are picture frame design and do not have a lot of thickness to them. I’m going to attempt to use a drum sander on a less trafficked room so that I can test out how the sander works first and hopefully get experienced enough to handle the higher traffic areas. Do you have any advice about this situation? Also can you discuss the need for an edger after this method of drum sanding?

  9. Please tell me if I am totally bonkers but I am thinking of sanding and oiling my floors by hand, but very very gradually – for the following reasons:
    I have 5 children and two dogs so blocking everyone out for however long it takes isn’t possible
    I have very little money so can’t afford hire of equipment or professionals
    The wood is unfinished but been uncovered for years so is quite knackered looking but I don’t mind that too much
    If I do three (or five?) boards at a time it will take forever but it’s something I’ll just do whenever I feel like it and minimal disruption
    I’ve redecorated the whole house myself in this way so I think I have the tenacity

    But please do tell me if I am bonkers

  10. Hi Ben. My floor have very…and i mean very thick coat of dark red varnish and the natural color of the floor is very light. What kind of sander would you recommend? And after 36g what shoild be the next sandpaper and what should i use for the finish? I want to completely remove the dark color and put a coat of some light color stain.

  11. HELP!. I plan on sanding my floors this weekend. I am a woman and 100 pounds and 5ft 5. I need advice on the best sander/s to use for my size. It’s just 2 rooms approximately 340SQ ft.

    Also How heavy are these machines? As I have to go up 4 steps into my building and need to be able to carry them up those steps.

    I can go to Lowes to Home depot to rent the machines, I just need ot know which will be easiest for someone my size to use and manage.

    1. the machines at those locations are generally lighter, but I would try and get a friend or neighbour to help you in an out to be sure!

  12. It is a very hard job to do, the results could be disappointing if you do not have the time to search and read, at the beginning it will look striped and clean but once you apply the stain that when you will know the mistakes. I will never do this again, not worth my time and effort, give it to professionals and rest.

  13. Hello,
    We just found wood planks under the carpet but they are white. We are going to sand them down and finish them. I’m hoping to do this correct.

  14. Does the grit change based on the wood? I’m preparing to refinish fir floors and a lot of DIYers seem to warn against using such low grits, especially for softwoods, warning that novices are more likely to damage floors with higher grits. The floors are generally in good condition, but there are some gouges in the floor from careless furniture dragging and stains from where a kitchen used to be in what is now a bed room. (I’m sure not all of this will come out.) I certainly want to take enough off to take out as much of the damage as possible, though I also am a little afraid of such a course grit.

    1. put on a 120 grit and practice, once you are used to the motion outlined in my guide then move onto courser grits, try 60 and if it does the trick great, if not jump down to 36 or 40. Most gouges are rarely much more deep than 1mm when they look about 4mm deep. Its very very rare indeed that marks from dragging furniture don’t come out, kitchen spills should come out too. Pet urine is the stuff you won’t get out

  15. Hello I am desperate for advice on quality of what has been laid so far in our house. I looked up all common mistakes in doing engineered floor and our guy has made them all. Is it possible to send you photos and see what your opinion is please? Thank you

    1. Hi John, I still have a lot more content to put up, but if you have any questions at all, feel free to ask them in the comments, or on the ask me a question page. Good luck! 🙂

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