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  • Sanding a concrete floor
  • Premier Icon piemonster
    Full Member

    I’ve a concrete floor to sand, this is in a basement (but well ventilated) room. The finish just needs to be good enough to take paint. Were not looking at a highly polished surface.

    What do I need to get this done? I have time and (several) random orbital Sanders? Beyond that, never really done anything like this.

    I also have PPE including a decent looking mask with replacement filters.

    Premier Icon carlos
    Full Member

    Can’t you just clean it and pour a self leveling screed?? Much easier and cleaner

    Premier Icon piemonster
    Full Member

    That would create other problems.

    I say basement,  but were on a split level ground floor being on a hill. So what I’m calling the basement has an external door, and 3 internal doors that would need trimming if the floor height was raised even a small amount.

    This is definitely in the territory of cleaning up the tatty elements and lobbing a paint of coat on top. But that coat does need to stick.

    Premier Icon Olly
    Free Member

    i had the same issue, rushed it and wasted a hundred quids worth of epoxy which just peeled off.
    It was brand new concrete though.

    I ended up hiring a diamond floor grinder from HSS for 2 days, and scrubbing maybe 3mm off the whole floor. Made a huge amount of dust, and was a wet process too, so a lot of slurry.
    Easy enough to do, and the concrete looked great. If i hadn’t already bought the new grey epoxy i would’ve used a transparent sealant.

    Is it a new floor? whats access like?

    Premier Icon piemonster
    Full Member

    Floor is old, decades at least. Access is as easy at it gets.

    Premier Icon Greybeard
    Full Member

    Sanding may wear out a lot of sandpaper. You’d be trying to wear away sand embedded in cement with sand glued to paper, which will win? Industrial floors are often ground with specialist grinding material. To get paint to stick you need a clean, dry, absorbent surface without dust. If it’s too highly polished it becomes non-absorbent. When concrete is compacted as it’s laid, the thin cement ‘laitance’ rises to the top and is worked with a float, but if it’s worked too much that layer becomes too impermeable and needs to be removed. That may have been part of the issue Olly had above – also, concrete needs at least 28 days to cure before painting, preferably longer.

    Lots of detail here.

    Premier Icon tazzymtb
    Full Member

    i would look to get some professional concrete finishers in. concrete is full of respirable crystaline silica (IARC classified carcinogen) and really rather not very good for you at all. unless your dust mask is an ffp3 and has been face fitted it wont afford much protection at all. if you want to do it yourself ideall you need to hire a proper concrete finishing surface grinder with a mobile extraction sustem for dust control, wear disposable overalls and a properly fited mask. its not something that you sould have a go at and then clean up with a hoover, as that will just redistribute the respirable fraction of the dust all over the place which is bit you really dont want in your lungs.

    Premier Icon jeffl
    Full Member

    Personally I’d self level the floor. Trimming the 3 internal doors will be easier and cleaner than grinding down the floor. Obviously the external door is the stumbling block. Is it wooden, UPVC or composite. If UPVC or Composite then it should be slightly higher than the internal floor anyway and not require trimming. If wooden then just trim it down, or if it has a storm board on the bottom trim the top and move the door up on the hinges and the lock etc.

    Appreciate it sounds like a lot of work but I’d say it’s easier than grinding.

    Edit: How big is the floorspace?

    Premier Icon deadlydarcy
    Free Member

    Wot tazzy and jeff said. I wouldn’t be sanding old concrete with personal PPE. If I was asked to do this on a site, it would only be with a full face mask and a functioning dust extraction system. First and foremost I’d be trying to avoid doing it at all.

    I think your best bet is to use a liquid dpm/primer on the concrete and then a thin skim of latex. Using the primer will give you good adhesion so you’re not having to depend on a deep build up of material for stability. Stick straight edges across the doors for a decent finish. Deal with trimming etc and just suck it up as part of the job.

    As much as latexing and door-trimming sounds like a ballache, I think it’s the easier of the two options.

    EDIT: Use a bottle mix latex, and leave a “handful” of powder in the bag. Better flow, like. 😀

    Premier Icon ollie_the_brave
    Free Member

    Presumably the external door has a cill, thus raising the floor with self levelling won’t affect that one.

    Just self level it, take off the doors and trim them to fit. It will be a MUCH neater and cleaner job and will be a hell of a lot faster than attempting to sand it.

    From what you’re describing, the cellar will be used for dry storage? thus it isn’t vital that it is absolutely bang on? If so, save your time, money and your lungs!

    Premier Icon dyna-ti
    Free Member

    You can hire a floor grinder. It’s like one of those industrial floor polishing machines only it uses carborundum blocks*
    *The old style, think now its more a disc set up.

    Take a look at whichever plant hire co is in your area and inquire there. Simply ask about concrete floor grinders and they’ll know what you’re after.

    Premier Icon andrewh
    Free Member

    Personally I’d self level the floor. Trimming the 3 internal doors will be easier and cleaner than grinding down the floor.

    That. Shouldn’t be too difficult

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