Floor flatness. It’s one of the biggest issues installers are faced with on a day-to-day basis for every category of flooring. Issues happen both on concrete and wood subfloors. So how are installers checking floor flatness? The use of string lines (Photo 1), straight edges (Photo 2) and lasers are common tools used.

For the past couple of years we’ve been using a laser to check for floor flatness. Now that we’ve run it through its paces I’ll share my thoughts. The laser is from Bosch and is a model GSL 2 surface laser (Photo 3). What we’ve found is that one person can check the flatness of the subfloor in an entire area within minutes and know how much the substrate is undulating. The tool paid for itself in the first couple of jobs where we had to check for flatness, and it’s a very visual way to show your client what areas of concern there are with the substrate.

There are two lasers on the tool. Once you set the tool on the subfloor and it self-levels, align the two lasers to where there is only one laser line visible; this is approximately 16” out from the tool. Once the two lasers are aligned, you’ll see that whenever the substrate is level, the lasers will maintain a single line. Where there is unevenness or undulation of the substrate, the lines will split.

Over a large area you may notice the line separating and coming back together in several areas. Take the target that comes with the kit and follow the instructions for aligning the target to the laser lines. What you’ll see is that the two laser lines form a “V”. Once you align the laser lines to the target, you will learn whether the particular spot where the lasers split marks a high spot or low spot (Photos 4-5).

There is also a remote control that allows the user to stand away from the laser and control the rotation speed and direction of the laser up to 60 feet. What I like about it is it only takes 4 AA alkaline batteries—and they actually last quite a while. You can also use the Bosch rechargeable 12-volt MAX battery, which you’ll have to purchase separately if you want it but we haven’t seen the need for it.

We like the fact that one person can check an entire area by themselves. The laser is small and comes with a carrying case which holds all the equipment necessary so we don’t have to have a straight edge, and the fact that you can check a distance of 60 feet just makes it that much better.

With subfloors having so many issues with flatness, for our company the tool is a money maker. Here’s to a flat world for us as installers!