How do I ensure my concrete floor is "flat" for laminate flooring?
I'm floating about 800 sq ft of bamboo over concrete. I have the entire area cleared of all previous flooring and fairly smooth. Now I'm trying to make sure it's flat,but I'm not really sure exactly how to do this.I've read the "string method" but I'm not really sure how to find the high spot across such a wide area (about 30'x25'). The room has a closet and a hallway too (i.e. it's not just square). I've also read about using a straight edge (like a 2x4), but when looking for gaps in 16ths of an inch, it seems a piece of 2x4 is not exact enough, even if I have a fairly "straight" piece of wood.
Other details: I tested for moisture using the plastic taped to the floor method and that seemed ok. The slab is about 25 years old and I live in a dry atmosphere (San Diego), so I think I'm ok with moisture and plan to use a 2in1 moisture barrier/foam padding.
Any tips would be greatly appreciated as I'm eager to start laying the flooring but don't want to skimp on the prep work. Help!
First: Water seeps at the same level. Use a long transparent tube (same tube used in aquarium pumps) with enough water to measure level points several inches above floor walls. You can fix one end of the tube on one area of the room, say 5 inches water level above the floor then on the opposite end of the tube, mark where the water level stops which should be the same 5 inches above the floor. Do this around your room and across areas you suspect floor is not level. Next, measure from the points you marked down to the floor as close as possible . Use the same measurement for all points. In theory, you marked points that are now level. Hammer a nail onto each of these points and string these nails. Connect these strings onto the nails across to create a network of strings. You'll see where your floor is not level.
The next question is that would you get into another trouble to level your floor before putting the laminates? It may not be necessary unless the floor is really uneven.