How to tell level-ness of concrete floor

Okay, I know this is probably a stupid question with an obvious answer, but...How do I tell if my concrete basement floor is level or not? It's not so bad that it's obviously wavy, but I don't want to plan on finishing the basement with an engineered wood floor only to find out that it's slightly out of level. I've heard as little as 10 mm over a 3m length will cause problems, but I am not sure how to detect this amount of dip or rise. Thanks for any help!
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On Thu, 11 Oct 2007 13:41:43 -0700, snipped-for-privacy@gmail.com wrote:

Level or flat?
For level, fill the room full of water and measure the depth at different places.
For flat use a long straight edge that you have verified is straight by putting it against something else that is flat.
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mm wrote:

Yup, hence my post.
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snipped-for-privacy@gmail.com wrote:

Lay a bit of steel angle iron over the surface and observe?
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clot wrote:

Sorry, should have added "and put a spirit level on it?"
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have to be an awfully large angle to use that as a guide. Any angle less than 2x2 inches and 5/16 thick will just bend with the floor.
s
wrote:

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Okay, thanks to everyone for the advice. What I'm really after I think is that it's flat. I don't actually want it level, since it currently slopes a little down toward the sump pump, which I think is good.
The concrete is 10 years old, and even with the super heavy rain storms this past year, we have NO water in the basement. The original owners installed a "Tuff-N-Dri" waterproofing system, including a "Warm-N-Dri insulating foam on the outside of the poured concrete walls, so even they aren't really as cold in the winter as some basement walls I've felt. So I'm fairly confident that the basement will remain dry, unless our water heater blows up.
So, basically I want to put down engineered hardwood flooring (DIY, I hope). My plan is to put down the Delta-FL underlayment, then the moisture/sound barrier, then the flooring. I figure the Delta-FL will do double-duty, one as insurance against some water eventually coming in (or from the water heater in case of catastrophe), and it should help make the end floor not so "hard". Several people have noted that the Delta-FL makes the floor "softer", more like a framed floor.
Anyway, in reading forums on this, several people have mentioned needing to level the floor with leveling compound, but all those posts seem to indicate a visibly uneven floor, whereas mine looks pretty good to the naked eye, even putting my face to the floor and scanning. But I'll take the advice here and try a bowling ball, marble, and water test. If anyone has any other advice based on this new info I've provided (on the even-ness of the floor or otherwise), it is all very much appreciated.
Thanks, M
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On Oct 11, 3:41 pm, snipped-for-privacy@gmail.com wrote:

Set a marble down on it. If it rolls away, the floor isn't level. Make sure it's a metric marble.
JK
P.S. Most basement floors are sloped towards the drain.
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I have a 14' aluminum straight edge that does the trick. Laser lines should do it too. You could also throw a bucket of water on the concrete floor.
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Set a bowling ball or simular round smooth object down on it and see if it rolls and where it rolls to.
On Oct 11, 3:41 pm, snipped-for-privacy@gmail.com wrote:

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snipped-for-privacy@gmail.com wrote:

Others noted the typical "hows", I'll only be pedantic and note it's "flat" you're looking for, not necessarily "level"... :)
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On Oct 11, 4:41 pm, snipped-for-privacy@gmail.com wrote:

Concrete specs frequently call out for (I'll let you do the conversions) the slab to be level within 1/8" within 10'. That's what's spec'd, not necessarily what they give you. That flat of a slab in a residential basement would be a minor miracle.
The easiest thing to do is to plan on patching the floor with compound. You can use a straightedge, say 6' or so, to locate the low spots. Then use self-leveling compound which pours on like soup and seeks its own level - you'll want to feather out the edges and move quickly. If you use a regular floor patching compound you can use the same straightedge as a screed to level off the patching compound. Make sure you wipe off the edge of the screed frequently. You may have to use latex bonding agent before applying the level compound depending on what's on the slab now.
You should also insure that you have a dry basement, and still take precautions against moisture wicking up through the slab. Verify that your intended flooring is approved for below grade installations. A significant number of them are not.
R
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snipped-for-privacy@gmail.com wrote:

The flooring won't care if it's level or not, within reason. It does need to be sound, dry, and flat. If you can't see a significant problem with a 8-10ft straight edge, or a ball, or water, you're unlikely to have any issues.
Since this is a basement, you need to pay attention to the moisture issues. Is it dry now? If not, correct that problem before installing a floor. Include a moisture barrier and follow ALL of the manufacturer's recommendations during the actual installation of the floor.
Oh, and I assume this concrete floor is "mature" and fully cured. If this is newly poured concrete there are quite a few additional issues to consider.
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On Oct 11, 4:43 pm, snipped-for-privacy@malch.com (Malcolm Hoar) wrote:

spray some water to see where it puddles and drains
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ransley wrote:

Agreed, provided you can dry it!
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get out the hose.....
water it down......
see where it goes....
s

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