Reading up on installing laminate flooring, I came across the warning that the floors must be flat for proper installation and use. Not necessarily level, but flat. IIRC, the specification was that there should be no deviation greater than 1/16 inch per 10 feet of floor space.
How does one go about checking/measuring the floor flatness?
I’m not a carpenter, but any straight object should work.
Maybe you already own a long level, yardstick or other object you believe to be perfectly straight? Lay it on the floor and look for gaps underneath.
yes a level or yardstick (on edge) would be a good indicator for that distance.
you could flood the floor and measure water depth around the room for greater accuracy, though you would need to suspend yourself from the ceiling to prevent waves so maybe that isn’t the bet method…
You might be able to rent a laser floor leveler. It can tell you where there may be low spots on the floor.
A Marble is an easy way. It will roll towards any dips in the floor.
You can get a large level with a nice flat edge for not too much, at least compared to the cost of the floor. I would read those directions again though because less than 1/16" over 10’ sounds a little too stringent to me. When I installed my floor it was more like 1/8" over 6’.
Tack a chalk line to the wall just above the floor on one side of the room, stretch it across the room to the other side just above floor level and see if it leaves any gaps or touches the floor in spots. You can use any old string, of course, but the chalk line will also leave high spots marked for you.
I suppose dragging a 4 or 6 foot straightedge across the floor would sorta work (but see last paragraph). And specs may very well be 1/8 inch over a span of 6 feet; it’s been a few months since I did my initial research. What’s not clear to me is how to detect bumps or divots of 1/8 inch or more (which isn’t very much) while dragging it.
I figure that there’s got to be some kind of commonly used contraption to do it – something akin to the parallel-pipes-with-board-laid-across-them setup I’ve seen used to level off sand/substrate when laying walkway pavers and such.
Also, again – I don’t care if the floor is level in this case, just whether it’s flat. So, flooding is out, as it checks for levelness, which is more stringent than I need. Same goes for using a marble. If I were to go this route, I’d likely just buy some leveling compound (like this, picked via googling) and do every room where the flooring was to be installed.
I suppose a chalk line (effectively a straightedge) would work to find bumps – mark opposite walls at 1/8 inch off the floor then drag. Not so good for divots, though. Also, I’d never heard of a laser floor level before and it sounds like a neat gadget that’d be useful in this situation…anyone have any experience with using one?
if you put the straightedge in many different spots and in different directions, then looking at the bottom edge you would see light from the other side where there is deviation.
Expanding on this idea, here’s a DIY contraption you could build: Get some straight, rigid, non-perforated U-channel stock, 3 or 4 feet long by an inch or two wide. Cap the ends with duct tape to form a long shallow box with one open side.
Put several LEDs along the inside channel of this box, powered by some AA batteries. Make sure both ends are light tight, so the only way for light to get out is through the open side.
Assuming the box has perfectly even and level edges, you now have the tool you need.
Lay the box open-side down on the floor to be checked. Turn off the room lights and make the environment as dark as possible. Move the box around to suspect areas of the floor and check for light leaks around its edges. If the floor stays dark, it is flat.
I’ve never actually done this myself – the idea just occurred to me while reading this thread. Maybe I should go patent this before posting…
And if you are in doubt about your long straightedge, just draw a line with it between two points, flip it over, and then redraw the line. Any deviation from straight will be obvious.
Okay, here’s a tedious but low-tech and cheap way to test from a former framer, who’s used to checking everything by stringing. You don’t need a long board. This will work for a wood floor, but not a concrete one.
Get three little wood blocks of the same thickness, and countersink for a sheetrock screw in two of them. Add a small nail with a head to the edge of the two blocks (5d box nails are good for this). Get a piece of mason’s twine or other not-too-stretchy string the width of your room. Tie a little loop at each end.
Now screw both blocks into the floor at opposite walls, and hook the string tight over the nails on the block, crossing the room. Get down on the floor and keep sliding that third block under the string and you can see how variable the floor is. You may have to set this across the room in many places, but it should give you a good idea of whether the floor is flat enough. On a really long span, even with a taut string it might droop a sixteenth or so in the middle, so keep that in mind.
Of course if you’re really thorough, you start by checking the perimeter of the room first.
This sounds like a real good time to hire the nice man who does this for a living and who will bring in his crew and equipment and do it right the first time while you are having a sixpack out on the patio. Life is just too short for some things.
It doesn’t have to be flat, it has to be SMOOTH. It can be a roller coaster and you can lay vinyl sheeting down. However if there are any bumps or holes it will show through. That means covering screws and filling in cracks or missing slivers of wood as well as ensuring the seam between boards is smooth.
Doing it yourself is not hard. Take an afternoon with some wood putty and a pad sander. It’s like cleaning a dirty skillet. When you get all the food bits off and it feels smooth you’re done with that section.
Carpenter here. Just weighing in to say dont kill yourself to try to achieve less than 1/16" deviation over 8’. That’s crazy. No floor is that flat. Glass isn’t that flat. I commonly see 1/4" over 2’ deviation in new home construction with engineered joists and subfloor. The manufacturer is just covering their butts here.
Use the string line or straightedge methods suggested above. Stringline is the way to go for larger areas. Fix the worst dips with leveling compound. Think visual. If you look at a glossy surface at an oblique angle and lighting you will see every imperfection. If you see the floor coming up a set of stairs for instance you will notice a lot more than if you are always viewing it from standing height.
I have never seen a hardwood floor installer level a subfloor. If there are obvious visual imperfections or ones you can feel walking, sure go and fix them. Properly installed laminate uses a quality underlay to take care of minor imperfections and reduce movement and squeaking. Laminate is a cheap flooring product (and most of it is garbage quite frankly). If you spend a bunch of time preparing the subfloor you are really saving nothing over actual pre-finished hardwood.
And honestly the flooring supplier can probably do a guaranteed install for less than $2 a foot. Is that really worth your time?
$2.00 a square foot! I just bought 12.3 mil laminate, in cappachino oak, foe $1.29 a square foot. It was a grand opening blowout sale and included the underlay. I don’t think I could justify spending 2 bucks a square to pay someone to put it down.
Within limited bounds – specifically, I’m thinking the length of one plank – it’s not clear to me that there is a practical difference. Especially considering the use of a decent underlayment.
I like the string suggestion, although it may be more trouble than it’s worth. Having not seen the condition of the concrete slab (buying a house; the carpets in there now are nasty and will be removed), I’m not sure what to expect.
And yes, it’s totally worth it to do it myself. 
Thinking some more about the flatness/smoothness, I wonder if it has an analogical similarity to Nyquist’s Law. That is, only [bumps | divots] of greater than 1/8 inch for any space of floor that is less than or equal to 1/2 the length of plank matter.
But, thinking about it even more, that would probably be true only if each plank floated independently, rather than being attached to each other via tongue-in-groove. Huh.
Perhaps over-analyzing, and perhaps even incorrect, but then musing about it suits my inner geek. 
I misread the op. I thought it was a question about vinyl flooring.:smack:
You would want a relatively flat floor for laminate flooring and you could check with a series of string lines. If it’s a concrete floor then it can be floated level/flat if it’s off. I’m not familiar with the different compounds used but I’ve removed some before that cracked to heck and back after pulling up tiles.
I’d think a decent 4’ aluminum level would be good enough. Move it a foot or two in different directions across the floor. If it rocks you’re on top of a high spot. If you can freely slide a piece of paper under it you’ve found a dip.