How to determine subfloor height difference?

Hi All,

First post however have been lurking for a while now. I am planning on laying some laminate timber flooring and am conscious of the need for a level substrate (concrete in my case.

The product I am laying (Parador Clever Click) says in regard to the subfloor that "irregularities exceeding 3mm per 1m have to be evened out". Now I have used a level around the room and there is some slight changes in the level however how can I tell how far out these changes are?

So my basic query is how do you determine the difference in height across a concrete subfloor?

Thanks very much for your help.

The easiest & quickest way I know to obtain accurate measurements is to get your hands on one o' those rotating laser levels doodads. A cheap'n'nasty from Bunnies will do.

Set it in the middle of the room and make sure it's dead level. I don't bother with the pathetic spirit levels they have built in, the footprint's too small for accuracy. Instead, I make a mark on one wall then use a water-level to make corresponding marks on the other three. It's straightforward to adjust the laser level until the beam is intersecting with all the marks.

Then, just walk around the room with a plumb-bob... I don't recommend just using a ruler as you can never be sure it's truly vertical... even a ruled spirit level only shows the angle of the face. First up mark the string where the laser hits it when the bob's just touching the floor. That'll give you a reference point to see how bad any variations are as you move the bob around the room. :)

Just run a straight edge over it, you'll soon see how good or bad it is.
Nice straight length of timber or metal around 2.4m long will do the trick.

stright edge is the go, when you can see under it or it is rocking you are in trouble. you will need to use a self leveling topping, just rember to prime the surface to ensure a good bond.