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Thread: uneven concrete floor

  1. #1
    DIYFK member jwm's Avatar


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    uneven concrete floor

    I'm close to done building my latest project, a 360-gallon plywood tank, 8 x 3 feet with a height of 2 feet. This will be going into my basement fishroom, an essentially unfinished space with a bare concrete floor. The biggest tank down there now is a 120-gallon, also homemade plywood-built. Additionally there is an assortment of tanks in other sizes, many homemade, all glass. I've made many stands, using essentially the construction method shown in Joey's video, with no problems. The existing 120 stands on 4 simple pillars of stacked concrete blocks.

    This new big stand poses some challenges in terms of levelling. I want to do the wood construction route so that I have storage space under the tank. My other stands have all been shimmed and otherwise braced and supported to achieve level. For the big stand, I don't really care to use shims; I want to maximize the contact area with the floor to spread out the pressure, rather than concentrating it on a few isolated spots under the stand. I'm toying with the notion of building a concrete pad to support the stand, similar to the pads on which machinery, transformers, switchgear, etc. is mounted in an industrial situation. I'm thinking of building a framework of 2x4's, affixing that to the floor, pouring concrete inside and then smoothing and levelling the new surface to support the stand. This will in simplest terms be a section of floor that is raised a couple of inches above the rest of the room.

    Incidentally, this doesn't need to be pretty. The stand, and for that matter the outside of the tank, will be unfinished wood. I'm not looking for furniture, I'm looking for utility.

    Anybody done this, or needed to do this? Is it really necessary? Or should I just build the stand, level it with shims, and then simply fill in the gaps with assorted sizes of other shims or wedges? I don't mind a bit of overkill, but I want to spend my time with fish, not tools; I don't want to go way overboard with this construction.

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    DIYFK member HillbillyHomer's Avatar


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    DIYFK member Meep's Avatar


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    As HillyBilly stated if it's not that far out of level you might want to consider floor leveling concrete, from experience you can mix the stuff down so it almost pours like water and is stupid easy to level... Trim a few wood shims (nothing big just little blocks) at the appropriate thickness grid them out say every three feet and using a dab (small) of white glue stick them to the floor so they don't move but can be removed without too much struggle... Now you have leveling pads to lay a straight edge across and screed the concrete across the top of the pads, no leveling guesswork when screeding the concrete when doing this with the pads... When that layer dries to touch and is still kind of soft after a few hours, use a small chisel and pry bar or whatever to remove all the wood pads and simply fill the small areas left behind with a new batch of leveling concrete using a putty knife to level... Away from the tank area you can just blend and feather the edges back into the original floor... Using the pads doesn't leave the 'seamless' look of a single pour but if you get some of that basement paint with the colored flecks you toss in it and paint it after you are done it leaves a real clean look... If you really want to look of a single pour, do the above but trim the pads about 1/16" shy of level, then when you remove them and patch all the holes, do one final thin 1/16" layer of leveler over the entire area, it's pretty easy to screed such a thin layer over a now level area even for an newbie due to the self leveling properties of the stuff when mixed real watery...

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    DIYFK member FLDave's Avatar


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    Didn't know we was sooo smart.......didja.....Click here to enlarge

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    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by FLDave Click here to enlarge
    Didn't know we was sooo smart.......didja.....Click here to enlarge
    I patched and leveled a lot of basement floors after jackhammering trenches in them to lay buried drains for bathrooms and to install ejection pits, a nice level floor makes it worlds easier to install showers, tubs, pedestal sinks, and do a nice tile job that actually lines up straight...

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    DIYFK member jwm's Avatar


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    Thank you, gentlemen! I had essentially no experience with any kind of masonry work; didn't even know there was such a thing as "self-levelling" concrete!

    Meep, I think I understand the method you are outlining, but I'm not sure why it's necessary? If this stuff is indeed self-levelling, and the application instructions seem to indicate that it is...why do I need to screed it at all? Couldn't I just build a form around the "footprint" of the tank, mix and pour enough of this stuff to achieve the minimum 1/8" thickness the instructions call for, and wait for it to level itself?

    It seems to me the biggest part of the job will be scuffing/grinding off the floor paint in that area. Or am I missing something here? (It's been known to happen...)

  7. #7
    DIYFK member Meep's Avatar


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    It's not 100% self leveling, it just levels a WHOLE lot easier than traditional concrete... Think of it like paint, if you drop blob on a table it does in fact 'self level' to some degree, same when you brush it on it mostly levels but ridges and peaks don't all go away before it dries, same with this stuff, it needs to be screeded to get it just that much closer...

    Also to get the best leveling you need to do this seamless, you can't stop and mix another batch, it has to be a continuous wet single pour, that is if you want the best self leveling with least work...

    What you said in regards to building a frame will work, you can screed across the top of the frame edges and get it flat, but that leaves 'edges' when you remove the frame, what I suggest allows you to feather it out to the surrounding floor for a clean job...

    Plus there is the experience factor, what I suggest makes it easier IMO, with more experience you can basically just pour it out and level with a concrete rake and be done, but that takes learning how the stuff works and that is a special touch that only comes with experience on using the screeding tools, kind of like the difference between a drywall mudders seams that are near perfect with no sanding vs an inexperienced mudder that will spend hours sanding to get a seam smooth...

  8. #8
    DIYFK member jwm's Avatar


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    Okay, I get it. I think I will combine the two ideas. Rather than placing a bunch of shims and trying to get all of them level with each other, I will just build a "dam" around the entire area and make sure the top is level all the way around. Then I can use the top of the dam as a guide and just run a straight-edge across from one end to the other on top of the dam. I'm not concerned about the edges when I remove the dam; might not even remove it! Leaving it in place would function to protect the corners from chipping. As I said, my fishroom is an unfinished basement, so the appearance of these edges is pretty immaterial to me.

    I'll get the floor paint removed now, but I'll need to wait a few weeks until the floor warms up a bit before I start with the concrete...plus I want to be able to work with the windows open, and our outdoor temps are just starting to creep up above freezing right now, so...Click here to enlarge

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